Class 7

SCERT AP 7th Class Maths Solutions Pdf Chapter 1 పూర్ణ సంఖ్యలు InText Questions and Answers.

AP State Syllabus 7th Class Maths Solutions 1st Lesson పూర్ణ సంఖ్యలు InText Questions

[పేజి నెం. 6]

ఖాళీలను పూరించుము.

ప్రశ్న 1.
7 × (- 4) = – (7 × 4) = ________
సాధన.
– 28

ప్రశ్న 2.
2 × (- 6) = – (2 × 6) = ________
సాధన.
– 12

నీ ప్రగతిని సరిచూసుకో [పేజి నెం. 8]

(i) 4 × (- 8)
సాధన.
4 × (- 8) = – (4 × 8) = – 32

(ii) 5 × (- 20)
సాధన.
5 × (20) = – (5 × 20) = – 100

(iii) 7 × (- 8)
సాధన.
7 × (- 8) = (7 × 8) = – 56

(iv) 10 × (- 9) ల విలువలను కనుక్కోండి.
సాధన.
10 × (- 9) = – (10 × 9) = – 90

[పేజి నెం. 8]

ఖాళీలను పూరించుము.

ప్రశ్న 1.
– 3 × 4 = _______ = 3 × (-4)
సాధన.
– 12

ప్రశ్న 2.
-4 × 4 = ________ = 4 × (4)
సాధన.
– 16

సుందరి

అన్వేషిద్దాం [పేజి నెం. 8]

ప్రశ్న 1.
4 × 5 నుంచి ప్రారంభించి (- 3) ×5 విలువ కనుగొనుటకు అమరికను వ్రాయుము.
సాధన.
4 × 5 = 20
3 × 5 = 15
2 × 5 = 10
1 × 5 = 5
0 × 5 = 0

(- 1) × 5 = -5
(-2) × 5 = – 10
(- 3) × 5 = – 15

ప్రశ్న 2.
5 × 3 నుంచి ప్రారంభించి (-7) × 3 విలువ కనుగొనుటకు అమరికను వ్రాయుము.
సాధన.
5 × 3 = 15
4 × 3 = 12
3 × 3 = 9
2 × 3 = 6
1 × 3 = 3
0 × 3 = 0

(- 1) × 3 = – 3
(- 2) × 3 = – 6
(- 3) × 3 = 9
(- 4) × 3 = – 12
(- 5) × 3 = – 15
(- 6) × 3 = – 18
(- 7) × 3 = – 21

[పేజి నెం: 8]

క్రింది విలువలను కనుగొనుము.
ప్రశ్న 1.
(- 6) × 7 = ________ = (6 × 7) = – 42
సాధన.
6 × (- 7)

ప్రశ్న 2.
(- 2) × 5 = ________ = – (2 × 5) = – 10
సాధన.
2 × (- 5)

ప్రశ్న 3.
(- 3) × 6 = ________ = – (3 × 6) = – 18
సాధన.
3 × (- 6)

ప్రశ్న 4.
(-4) × 5 = ________ = – (4 × 5) = – 20
సాధన.
4 × (- 5)

నీ ప్రగతిని సరిచూసుకో [పేజి నెం. 8]

ప్రశ్న 1.
(i) (- 6) × 5
సాధన.
(- 6) × 5 = (6 × 5) = – 30

(ii) (-15) × 2
సాధన.
(- 15) × 2 = -(15 × 2) = – 30

(iii) (-12) × 8
సాధన.
(- 12) × 8 = -(12 × 8) = – 96

(iv) (-10) × 6 ల విలువలను కనుక్కోండి.
సాధన.
(- 10) × 6 = (10 × 6) = – 60

క్రింది విలువలను కనుగొనుము. [పేజి నెం. 8]

ప్రశ్న 1.
(- 2) × (- 4) = _____
సాధన.
8

ప్రశ్న 2.
– 2 × (- 5) = _____
సాధన.
10

నీ ప్రగతిని సరిచూసుకో [పేజి నెం. 10]

ప్రశ్న 1.
(- 5) × 3 నుంచి ప్రారంభించి (-5) × (- 4) విలువ కనుగొనుటకు అమరికను వ్రాయుము.
సాధన.
(- 5) × 3 = – 15
(- 5) × 2 = – 10
(- 5) × 1 = – 5
(- 5) × 0 = 0
(- 5) × (- 1) = 5
(- 5) × (- 2) = 10
(- 5) × (- 3) = 15
(- 5) × (- 4) = 20

ప్రశ్న 2.
(- 7) × 5 నుంచి ప్రారంభించి (-7) × (-2) విలువ కనుగొనుటకు అమరికను వ్రాయుము.
సాధన.
(- 7) × 5 = – 35
(- 7) × 4 = – 28
(- 7) × 3 = – 21
(- 7) × 2 = – 14
(- 7) × 1 = – 7
(- 7) × 0 = 0
(- 7) × (- 1) = 7
(- 7) × (- 2) = 14

ఇవి చేయండి కృత్యం [పేజి నెం. 12]

క్రింది పట్టికలో మొదటి నిలువు వరుసలో ప్రతి సంఖ్యను, మొదటి అడ్డు వరుసలోని ప్రతి సంఖ్యతో గుణిస్తూ పట్టికను పూరించుము మరియు ఇవ్వబడిన ప్రశ్నలకు సమాధానాలు ఇవ్వండి.

సాధన.

ప్రశ్న 1.
పట్టిక నుండి మీరు ఏమి గమనించారో వ్రాయండి.
సాధన.
పై పట్టిక నుండి గమనించిన అంశాలు :

• రెండు ధన పూర్ణ సంఖ్యల లబ్దం ధనపూర్ణసంఖ్య.
• ఒక ధన పూర్ణ సంఖ్య, ఒక రుణ పూర్ణ సంఖ్యల లబ్దం రుణ పూర్ణ సంఖ్య.
• పూర్ణ సంఖ్య, ‘O’ (సున్న) ల లబ్దము సున్న.
• ఒక పూర్ణ సంఖ్యను 1 చే గుణించిన లబ్దము అదే పూర్ణసంఖ్య అవుతుంది.

ప్రశ్న 2.
పూర్ణసంఖ్యను (-1) చే గుణకారం చేసినపుడు ఏమవుతుంది ?
సాధన.
పూర్ణసంఖ్యను (-1)చే గుణకారము చేసినపుడు ఆ పూర్ణ సంఖ్య యొక్క గుర్తు మారుతుంది.

ప్రశ్న 3.
రెండు పూర్ణసంఖ్యల లబ్ధము సున్నా ఎప్పుడు అవుతుంది ?
సాధన.
రెండు పూర్ణ సంఖ్యలలో ఏదేని ఒక్కటి సున్న అయినపుడు, లేదా ఆ రెండు పూర్ణ సంఖ్యలు సున్నా అయినపుడు ఆ రెండు పూర్ణ సంఖ్యల లబ్ధము సున్న అవుతుంది.

[పేజి నెం. 16]

పూర్ణసంఖ్యల భాగహారము:
క్రింది పట్టికను పరిశీలించి, మిగిలిన ఖాళీలను పూరించండి.

Answer:

నీ ప్రగతిని సరిచూసుకో [పేజి నెం. 18]

ప్రశ్న 1.

సాధన.

ఇవి చేయండి కృత్యం [పేజి నెం. 20]

ప్రశ్న 1.
పక్క కొలనులోని చేపలపై కొన్ని సంఖ్యలు ఉన్నవి. ఏవేని 4 జతల సంఖ్యలను ఎన్నుకొని, 4 గుణకార వాక్యాలు రాయుము. తరువాత 4 జతల ఇతర సంఖ్యలను ఎన్నుకొని, 4 భాగహార వాక్యాలు రాయుము.

సాధన.
గుణకార వాక్యాలు:

• (-10) × 6 = – 60
• 12 × 8 = 96
• 6 × (-4) = – 24
• (4) × (-9) = 36
• (-56) × (- 10) = 560

భాగహార వాక్యాలు:

• – 36 + 6 = – 6
• 72 + 8 = 9
• (- 24) + 6 = 4
• (- 100) + (- 10) = 10
• 18 + (- 9) = – 2

పజల్ టైమ్ [పేజి నెం. 22]

జశ్వి తన ఇష్టమైన సంఖ్యను ఒక పజిల్ రూపములో చెప్పినది. ఆ సంఖ్యను కనుగొనండి.

సాధన.

పేజి నెం. 22

(i) సంవృత ధర్మము : కింది పట్టికలను పరిశీలించండి మరియు వాటిని పూరించుము.

సాధన.

∴ పూర్ణ సంఖ్యలు సంకలనము, గుణకారముల దృష్ట్యా సంవృత ధర్మాన్ని పాటిస్తాయి.

ఆలోచించండి [పేజి నెం. 22]

మొత్తము లేదా లబ్దము పూర్ణ సంఖ్య కాని సంఖ్య అగునట్లు కనీసం ఒక పూర్ణ సంఖ్యల జత చెప్పగలమా ?
సాధన.
మొత్తము లేదా లబ్దము పూర్ణ సంఖ్య కాని సంఖ్య అగునట్లు కనీసం ఒక పూర్ణ సంఖ్యల జత సాధ్యము కాదు.

[పేజి నెం. 24]

సాధన.

∴ పూర్ణ సంఖ్యలు వ్యవకలనం దృష్ట్యా సంవృత ధర్మాన్ని పాటిస్తాయి. కానీ భాగహారము దృష్ట్యా సంవృత ధర్మాన్ని పాటించనవసరం లేదు.

(ii) వినిమయ (స్థిత్యంతర) న్యాయము: కింది పట్టికలను పరిశీలించండి మరియు వాటిని పూరించుము. సంకలనం

సాధన.

∴ పూర్ణ సంఖ్యలు సంకలనము మరియు గుణకారముల దృష్ట్యా వినిమయ (స్థిత్యంతర) న్యాయమును పాటిస్తాయి.

సాధన.

∴ పూర్ణ సంఖ్యలు వ్యవకలనము మరియు భాగహారముల దృష్ట్యా వినిమమ (స్థిత్యంతర) న్యాయమును పాటించవు.

(iii) సహచర న్యాయము: కింది పట్టికలను పరిశీలించండి మరియు వాటిని పూరించుము.

సాధన.

∴ పూర్ణ సంఖ్యలు సంకలనము మరియు గుణకారముల దృష్ట్యా సహచర న్యాయము పాటిస్తాయి.

సాధన.

∴ పూర్ణ సంఖ్యలు వ్యవకలనము మరియు భాగహారముల దృష్ట్యా సహచర న్యాయమును పాటించవు.

(iv) తత్సమ ధర్మము: ఈ క్రింది పట్టికలను గమనించి, పూరించండి.

సాధన.

[పేజి నెం. 28]

v. సంకలన విలోమ న్యాయము :
– 3 కు ఎంత కలిపిన సంకలన తత్సమాంశము ‘0’ వచ్చును ?
సాధన.
జ. పరిశీలన :

• 4 + (- 4) = 0
• (- 5) + 5 = 0
• (- 6) + 6 = 0

నీ ప్రగతిని సరిచూసుకో [పేజి నెం. 28 ఉదాహరణ]

5, -8, 1, 0 ల సంకలన విలోమాలను వ్రాయుము.
సాధన.
5 యొక్క సంకలన విలోమం = – (5) = – 5
-8 యొక్క సంకలన విలోమం = – (-8) = 8
1 యొక్క సంకలన విలోమము = – (1) = – 1
0 యొక్క సంకలన విలోమము = – (0) = 0

ఆలోచించండి [పేజి నెం. 28]

ప్రశ్న 1.
6ను ఏ సంఖ్యతో గుణించిన గుణకార తత్సమాంశము ‘1’ వస్తుంది ? అది పూర్ణ సంఖ్యలలో వుంటుందా?
సాధన.
6 ను \(\frac{1}{6}\) తో గుణించిన గుణకార తత్సమాంశము 1 వస్తుంది.
6 × \(\frac{1}{6}\) = 1
\(\frac{1}{6}\) పూర్ణ సంఖ్యలలో ఉండదు.

ప్రశ్న 2.
– 3 × [(- 4) – 2] = [(- 3) × (-4)] – [(- 3) × 2)ను సరిచూడుము. పూర్ణసంఖ్యలు వ్యవకలనముపై గుణకారము విభాగ న్యాయమును పాటిస్తాయా ? మీ పరిశీలనలను వ్రాయండి.
సాధన.
– 3 × [(- 4) – 2] = [(- 3) × (- 4)] – [(- 3) × 2]
– 3 × (-6) = 12 — (-6)
18 = 18
ప్రతి సందర్భములోనూ ఎడమచేతి వైపు ఉన్న విలువ, కుడిచేతి వైపు ఉన్న విలువకు సమానము.
కావున, పూర్ణసంఖ్యలు వ్యవకలనముపై గుణకారము విభాగ న్యాయమును పాటిస్తాయి.

నీ ప్రగతిని సరిచూసుకో [పేజి నెం. 34]

సూక్ష్మీకరించుము:
(i) 5 × 6 – 6
సాధన.
5 × 6 – 6
= 30 – 6
= 24
(BODMAS నియమం ప్రకారం గుణకారం, ఆ తర్వాత వ్యవకలనం)

(ii) 24 ÷ 3 × 3 – 30
సాధన.
24 ÷ 3 × 3 – 30
= 8 × 3 – 30
= 24 – 30
= – 6
(BODMAS నియమం ప్రకారం మొదట భాగహారం, ఆ తరువాత గుణకారం, ఆ తరువాత వ్యవకలనం)

(iii) 5 × 5 – 5 ÷ 5 + 5
సాధన.
5 × 5 – 5 ÷ 5 + 5
= 5 × 5 – 1 + 5
= 25 – 1 + 5
= 30 – 1
(BODMAS నియమం ప్రకారం సూక్ష్మీకరణ క్రమం: భాగహారం, గుణకారం, సంకలనం, వ్యవకలనం)

అన్వేషిద్దాం [పేజి నెం. 38]

|x| = 15 అయిన x యొక్క విలువ ఏమవుతుంది ? చర్చించండి.
సాధన.
|x| = 15 అయిన x = 15 లేదా X = – 15 అవుతుంది.
వివరణ (i): .
ఎందుకనగా, |15| = 15 మరియు |- 15| = 15

వివరణ (ii):
x > 0 అయిన |x| = x
x < 0 అయిన |x| = – x .
|x| = 15 లో
x > 0 అనగా x ధనాత్మకం అయిన x = 15
x < 0 అనగా x రుణాత్మకం అయిన x = – 15

తార్కిక విభాగం

సంఖ్యాశ్రేణులు – 1 [పేజి నెం. 40]

ఒక ప్రత్యేక నియమము లేదా ప్రత్యేక అమరిక ఆధారంగా ఏర్పడిన సంఖ్యల సమాహారమే సంఖ్యా శ్రేణులుగా పరిగణించవచ్చు. ఒక పదమునకు దాని ముందు పదమునకు మధ్య సంబంధం ఏ విధంగా ఉందో, ఆ శ్రేణిలోని అన్ని పదాల మధ్య అదే విధంగా ఉండును. మనం శ్రేణిలోని పదాలు ఏ నియమం ప్రకారం ఏర్పడ్డాయో కనుగొని, ఆ నియమం ఆధారంగా మనకు తెలియని సంఖ్యను కనుగొనాలి. కొన్ని రకాల శ్రేణులు కింద ఇవ్వబడ్డాయి.

1. ప్రధాన సంఖ్యలు శ్రేణి : ,ఇందులో ప్రధాన సంఖ్యలు క్రమంలో ఉండును.
ఉదా (i) : 2, 3, 5, 7, 11, 13, ____.
ఈ శ్రేణిలో వరుస ప్రధాన సంఖ్యలు ఉన్నాయి. 13 తర్వాత వచ్చు ప్రధాన సంఖ్య 17.
కావున, సమాధానము 17.

ఉదా (ii): 2, 5, 11, 17, 23,
ఈ శ్రేణిలో ప్రత్యామ్నాయ (ఒకటి వదిలి మరొకటి) ప్రధాన సంఖ్యలు ఉన్నాయి. 23 తర్వాత వచ్చు ప్రధాన సంఖ్యలు 29, 31. కావున, సమాధానము 31.

2. సంకలన శ్రేణి : ఈ శ్రేణిలో ప్రతి సంఖ్య దాని ముందున్న సంఖ్యకు, ఒక ప్రత్యేక సంఖ్య లేదా శ్రేణిని కలుపగా ఏర్పడును.
ఉదా (i) : 7, 10, 13, 16, 19, 22, ____.
కావున, సమాధానము = 22 + 3 = 25

ఉదా (ii): 10, 14, 19, 25, 32, _____.
కావున, సమాధానము = 32 + 8 = 40

ఉదా (iii) : 5, 7, 10, 15, 22, ______.

ప్రతి సంఖ్య వరుస ప్రధాన సంఖ్యలను కలుపగా ఏర్పడుచున్నది. కావున, సమాధానము
= 22 + 11 = 33.

3. ఫిబోనాకి శ్రేణి : ఇందులో మూడవ సంఖ్య నుండి ప్రతీ సంఖ్య దాని ముందున్న రెండు సంఖ్యల మొత్తముగా ఉండును.
ఉదా (i) : 3, 5, 8, 13, 21, ______.
ఇక్కడ మూడవ సంఖ్య నుండి,
3 + 5 = 8,
5 + 8 = 13,
8 + 13 = 21,
కావున, సమాధానము = 13 + 21 = 34
ఉదా (ii): 6, 10, 16, 26, 42, ______.
ఇక్కడ మూడవ సంఖ్య నుండి,
6 + 10 = 16,
10 + 16 = 26,
16 + 26 = 42,
కావున, సమాధానము = 26 + 42 = 68

ఉదాహరణలు:

ప్రశ్న 1.
నీటి గుంట(సంప్) పూర్తిగా నీటితో నిండి వుంది. మోటారుతో నీటిని తోడడం వలన నీటి స్థాయి నిముషానికి 2 అంగుళాల చొప్పున తగ్గిన 20 నిముషాల తరువాత నేలమట్టము నుండి నీరు ఎంత లోతులో ఉంటుంది ?
సాధన.
ఒక నిముషములో నీటి మట్టములో మార్పు = -2 అంగుళాలు (2 అంగుళాలు తగ్గినది)
20 నిముషాల తరువాత నీటి మట్టములో మార్పు = 20 × (- 2) = – 40 అంగుళాలు
కావున, నీటి గుంటలో నీరు నేల మట్టము నుండి 40 అంగుళాల లోతులో ఉండును.

ప్రశ్న 2.
భూమి నుంచి 20 మీ. ఎత్తు నుంచి ఒక లిఫ్ట్ ప్రారంభమయింది. అది గని లోపలికి నిముషానికి 6 మీ. చొప్పున కిందికి వెళ్ళిన, 15 నిముషాల తరువాత దాని స్థానము ఏమిటి ?
సాధన.
లిఫ్ట్ కిందికి వెళ్తున్నది కావున అది వెళ్ళే దూరాన్ని ఋణ పూర్ణ సంఖ్యతో సూచిస్తాము.
ఒక నిముషంలో లిఫ్ట్ యొక్క స్థానములో మార్పు = – 6 మీ.
15 నిముషాలలో లిఫ్ట్ యొక్క స్థానములో మార్పు = 15 × (- 6) = – 90 మీ.
కనుక, లిఫ్ట్ యొక్క చివరి స్థానము = 20 + (- 90) = -70 మీ.
∴ లిఫ్ట్ నేల మట్టము నుండి 70 మీ. లోతులో ఉండును.

ప్రశ్న 3.
ఒక పరీక్షలో రాయబడిన సరైన సమాధానానికి (+5) మార్కులు మరియు తప్పు అయిన సమాధానానికి (-3) మార్కులు కేటాయించడం జరిగింది. లక్ష్మి రాసిన సమాధానాలలో 45 సరైనవి మరియు 15 తప్పు అయిన ఆమెకు వచ్చిన మార్కులు ఎన్ని?
సాధన.
ఒక సరైన సమాధానానికి ఇవ్వబడ్డ మార్కులు = 5
45 సరైన సమాధానాలకు మార్కులు = 45 × 5 = 225
ఒక తప్పు సమాధానానికి ఇవ్వబడ్డ మార్కులు = – 3
15 తప్పు సమాధానాలకి ఇవ్వబడ్డ మార్కులు = 15 × (- 3) = – 45
∴ లక్ష్మికి వచ్చిన మార్కులు = 225 + (- 45) = 180

ప్రశ్న 4.
భూ ఉపరితలం నుంచి ఒక బోర్ వెల్ యంత్రం ప్రతి గంటకు 72 అడుగుల లోతును త్రవ్వగలదు. భూ ఉపరితలం నుంచి 360 అడుగుల లోతులో ఉన్న నీటి పొరను చేరుటకు ఆ యంత్రానికి ఎంత సమయం పడుతుంది ?

సాధన.
ఒక గంటలో త్రవ్వు లోతు = – 72 అడుగులు
భూ ఉపరితలము నుండి నీటిపొర గల దూరము = -360 అడుగులు
నీటిని చేరుటకు పట్టు సమయము = -360 ÷ (- 72) = 5
కావున, బోర్‌వెల్ యంత్రం నీటి పొరను చేరుటకు 5 గంటల సమయం పడుతుంది.

ప్రశ్న 5.
ఒక పరీక్షలో, ప్రతి సరైన సమాధానానికి (+ 4) మార్కులు మరియు ప్రతి తప్పు సమాధానానికి (- 2) మార్కులు ఇవ్వబడతాయి. శశి అన్ని ప్రశ్నలకు సమాధానం ఇచ్చాడు మరియు అతను వ్రాసిన 8 సరైన సమాధానాల ద్వారా 26 మార్కులు సాధించాడు. శశి రాసిన తప్పు సమాధానాలు ఎన్ని ?
సాధన.
ఒక్కొక్క సరైన సమాధానానికి మార్కులు = 4
కనుక, 8 సరైన సమాధానాలకు మార్కులు = 4 × 8 = 32
శశికి వచ్చిన మార్కులు = 26
తప్పు సమాధానాలకు ఇవ్వబడిన మార్కులు = 26 – 32 = – 6
ఒక్కొక్క తప్పు సమాధానానికి మార్కులు = – 2
∴ తప్పు సమాధానాల సంఖ్య = (- 6) ÷ (- 2) = 3

ప్రశ్న 6.
దుకాణదారుడు యాసిన్ ఒక సోనా మసూరి బియ్యపు బస్తాపై ₹20 లాభముతో మరియు హంస బియ్యపు బస్తాపై ₹12 నష్టముతో అమ్మాడు. ఒక నెలలో 1440 సోనా మసూరి బియ్యపు బస్తాలు అమ్మిన లాభము కానీ, నష్టము కానీ రాలేదు. అయిన ఆ నెలలో ఎన్ని హంస బియ్యపు బస్తాలు అమ్మాడు ?
సాధన.
ఇచ్చిన సమస్యలో, లాభము కానీ, నష్టము కానీ లేదు.
కావున, వచ్చిన లాభము + వచ్చిన నష్టము = 0
వచ్చిన లాభము = – వచ్చిన నష్టము
ఒక సోనా మసూరి బియ్యపు బస్తాపై వచ్చు లాభము = ₹ 20
1440 సోనా మసూరి బియ్యపు బస్తాలపై వచ్చు లాభము = 1440 × 20 = ₹ 28800
హంస బియ్యపు బస్తాలపై వచ్చు నష్టము = ₹ – 28800
ఒక హంస బియ్యపు బస్తాపై వచ్చు నష్టము = ₹ 12, దీనిని మనం – 12గా సూచిస్తాం.
ఆ నెలలో అమ్మిన హంస బియ్యపు బస్తాల సంఖ్య = (-28800) ÷ (-12) = 2400 బస్తాలు.

ప్రశ్న 7.
(+2) మరియు (-3)ల సంకలన విలోమాలను వ్రాయుము.
సాధన.
+2 సంకలన విలోమము = -(+2) = – 2
-3 సంకలన విలోమము = -(-3) = + 3

ప్రశ్న 8.
క్రింది వాటిని సహచర న్యాయము ఆధారంగా గుణకారము చేయండి.
(i)
– 25 ×(4) × 2 × (-8)
సాధన.
– 25 × (4) × 2 × (- 8)
= [- 25 × (-4)] × 2 × (- 8)
= [100 × 2] × (- 8)
= 200 × (- 8) = – 1600

(ii) (- 20) × (-2) × (- 5) × 1
సాధన.
(- 20) × (- 2) × (- 5) ×7
= (- 20) × [(- 2) × (- 5)] × 7
= [(- 20) × 10] ×7
= – 200 × 7 = – 1400

ప్రశ్న 9.
(-42) × (-7) మరియు (-7) × (-42) లు సమానమా ? ఇది ఏ న్యాయము ?
సాధన.
(- 42) × (-7) = + 294
(- 7) × (42) = + 294
∴ (- 42) × (- 7) = (- 7) × (42)
ఇది గుణకార వినిమయ (స్థిత్యంతర) న్యాయము.

ప్రశ్న 10.
26 × (- 48) + (- 48) × (- 36) ను తగిన న్యాయాలను ఉపయోగించి సూక్ష్మీకరించుము.
సాధన.
26 × (-48) + (- 48) × (- 36)
= (- 48) × 26 + (- 48) × (- 36) (వినిమయ న్యాయము)
= (- 48) × [26 + (- 36)] (విభాగ న్యాయము)
= (48) × (- 10) = 480

ప్రశ్న 11.
3 × 2 + 8 ÷ 4 సూక్ష్మీకరించుము.
సాధన.
3 × 2 + 8 ÷ 4 (భాగహారము)
= 3 × 2 + 2 (గుణకారము)
= 6 + 2 (సంకలనము)
= 8

ప్రశ్న 12.
1 × 6 – \(\overline{8-4}\) సూక్ష్మీకరించుము.
సాధన.
7 × 6 – \(\overline{8-4}\) (విన్కులం)
= 7 × 6 – 4 (గుణకారము)
= 42 – 4 (వ్యవకలనము)

ప్రశ్న 13.
18 + 64 – 4 {26 – (14 – \(\overline{7-3}\)} సూక్ష్మీకరించుము.
సాధన.
18 + 64 -4 {26 – (14 – \(\overline{7-3}\))} (విన్కులం)
= 18 + 64 ÷ 4 {26 – (14 – 4)} (సాధారణ బ్రాకెట్)
= 18 + 64 ÷ 4 {26 – 10} (కర్లీ బ్రాకెట్)
= 18 + 64 ÷ 4 {16} (ఆఫ్)
= 18 + 64 ÷ 64 (భాగహారము)
= 18 ÷ 1 (సంకలనము)
= 19

సాధనా ప్రశ్నలు [పేజి నెం. 42]

ప్రశ్న 1.
12, 19, 26, 33, 40, 47, ______
(a) 57
(b) 54
(c) 52
(d) 50
సాధన.
(b) 54

వివరణ:

ప్రశ్న 2.
2, 13, 24, 35, 46, 57, _____
(a) 65
(b) 67
(c) 68
(d) 72
సాధన.
(c) 68

వివరణ:

ప్రశ్న 3.
61, 67, 71, 73, 79, ______
(a) 89
(b) 87
(c) 85
(d) 83
సాధన.
(d) 83

వివరణ:

ప్రశ్న 4.
3, 7, 13, 21, 31,
(a) 43
(b) 48
(c) 51
(d) 53
సాధన.
(a) 43

వివరణ:

ప్రశ్న 5.
8, 12, 20, 32, 52, 84, _______
(a) 111
(b) 126
(c) 136
(d) 174
సాధన.
(c) 136

వివరణ: 8, 12, 20, 32, 52, 84, 136 (ఫిబోనాకి శ్రేణ)
8 + 12 = 20
12 + 20 = 32
20 + 32 = 52
32 + 52 = 84
52 + 84 = 136

ప్రశ్న 6.
23, 28, 38, 53, 73, 98, __
(a) 121
(b) 128
(c) 135
(d) 146
సాధన.
(b) 128

వివరణ:

ప్రశ్న 7.
101, 97, 89, 83, 79, 73, 71, _____
(a) 61
(b) 65
(c) 66
(d) 67
సాధన.
(d) 67

వివరణ: వరుస ప్రధాన సంఖ్యలు.
71 కి వెంటనే ముందున్న ప్రధాన సంఖ్య = 67

ప్రశ్న 8.
4, 7, 11, 18, 29, 47, __
(a) 67
(b) 76
(c) 84
(d) 92
సాధన.
(b) 76

వివరణ: ఫిబోనాకి శ్రేణి
4 + 7 = 11,
7 + 11 = 18,
11 + 18 = 29,
18 + 29 = 47,
29 + 47 = 76
4, 7, 11, 18, 29, 47, 76

ప్రశ్న 9.
76, 187, 298, 409, 520, ______
(a) 631
(b) 656
(c) 701
(d) 724
సాధన.
(a) 631

వివరణ: 61, 67, 71, 73, 79, 83

ప్రశ్న 10.
0, 2, 5, 10, 17, 28, 41, ______
(a) 50
(b) 53
(c) 57
(d) 58
సాధన.
(d) 58

వివరణ:

ప్రశ్న 11.
36, 45, 53, 60, 66, 71, ____
(a) 84
(b) 78
(c) 75
(d) 73
సాధన.
(c) 75

వివరణ:

ప్రశ్న 12.
0, 15, 45, 90, 150, 225, _____
(a) 295
(b) 300
(c) 315
(d) 360
సాధన.
(c) 315

వివరణ:

15, 30, 45, 60, 75 లు 15 గుణిజాలు.
కావున, 75 తరువాత గల 15 గుణిజము 90.

ప్రశ్న 13.
18, 23, 25, 30, 32, 37, _____ .
(a) 43
(b) 41
(c) 39
(d) 38
సాధన.
(c) 39

వివరణ:

ప్రశ్న 14.
4, 7, 11, 18, 29, 47, ______
(a) 71
(b) 76
(c) 77
(d) 82
సాధన.
(b) 76

వివరణ: ఫిబోనాకి శ్రేణి
4 + 7 = 11,
7 + 11 = 18,
11 + 18 = 29,
18 + 29 = 47,
∴ 29 + 47 = 76
4, 7, 11, 18, 29, 47, 76

ప్రశ్న 15.
12, 18, 21, 27, 30, 36, 39, _____
(a) 43
(b) 45
(c) 49
(d) 52
సాధన.
(b) 45

వివరణ:

SCERT AP 7th Class Maths Solutions Pdf Chapter 1 పూర్ణ సంఖ్యలు Unit Exercise Questions and Answers.

AP State Syllabus 7th Class Maths Solutions 1st Lesson పూర్ణ సంఖ్యలు Unit Exercise

ప్రశ్న 1.
క్రింది వాటిని లెక్కించుము. సాధన.
(i) 8 × (- 1)
సాధన.
8 × (-1)
a × (-b) = – (a × b) అని మనకు తెలుసు.
= – (8 × 1) = – 8

(ii) (- 2) × 175
సాధన.
(- 2) × 175
(- a) × b = – (a × b) అని మనకు తెలుసు.
= – (2 × 175)
= – 350

(iii) (- 3) × (- 40)
సాధన.
(- 3) × (40)
(- a) × (- b) = (a × b) అని మనకు తెలుసు.
= (- 3) × (40)
= 3 × 40 = 120

(iv) (- 24) × (- 7)
సాధన.
(- 24) × (27)
(- a) × (- b) = (a × b) అని మనకు తెలుసు.
= 24 × 7 = 168

(v) (- 7) ÷ (- 1)
సాధన.
(- 7) ÷ (- 1)
(- a) ÷ (-b) = a ÷ b అని మనకు తెలుసు.
= (- 7) ÷ (- 1) = 7 ÷ 1 = 7

(vi) (- 12) ÷ (+ 6)
సాధన.
(- 12) ÷ (+ 6)
(- a) ÷ b = – (a ÷ b) అని మనకు తెలుసు.
= (- 12) ÷ 6 = – 2

(vii) (- 49) ÷ (-7)
సాధన.
(49) ÷ (-7)
(- a) ÷ (- b) = a ÷ b అని మనకు తెలుసు.
= (- 49) ÷ (- 7) = 49 ÷ 7 = 7

(viii) (+ 63) ÷ (- 9)
సాధన.
(+ 63) ÷ (- 9)
a ÷ (- b) = – (a ÷ b) అని మనకు తెలుసు.
= 63 ÷ (- 9) = – (63 ÷ 9) = – 7

ప్రశ్న 2.
క్రింది వాక్యాలు సత్యమయ్యే విధముగా ఖాళీలను పూర్ణసంఖ్యలతో భర్తీ చేయుము.
(i) (- 7) × _____ = 21
సాధన.
(- 7) × x = 21
x = 21 ÷ (-7)
a ÷ (- b) = – (a ÷ b) అని మనకు తెలుసు.
x = – (21 ÷ 7)
∴ x = – 3

(ii) 7 x _______= – 42
సాధన.
7 × x = 42
x = (- 42) ÷ 7.
(- a) ÷ b = – (a ÷ b) అని మనకు తెలుసు.
x = – (42 ÷ 7)
∴ x = – 6

(iii) _______ × (9) = – 72
సాధన.
x × (- 9) = – 72
x = (- 72) ÷ (- 9)
(- a) ÷ (-b) = (a ÷ b) అని మనకు తెలుసు.
x = (72 ÷ 9)
∴ x = 8

(iv) _______ × (- 11) = 132
సాధన.
x × (- 11) = 132
x = 132 ÷ (- 11)
a ÷ (-b) = – (a ÷ b) అని మనకు తెలుసు.
x = – (132 ÷ 11)
∴ x = – 12

(v) (- 25) ÷ ______ = 1.
సాధన.
(- 25) ÷ x = 1 .
x = (- 25) ÷ 1
(- a) ÷ b = – (a ÷ b) అని మనకు తెలుసు.
x = (- 25 ÷ 1)
∴ x = – 25

(vi) 42 ÷ ____ = – 6
సాధన.
42 ÷ x = – 6
42 = (- 6) × x
x = 42 ÷ (- 6)
a ÷ (- b) = – (a ÷ b) అని మనకు తెలుసు.
x = – (42 ÷ 6)
∴ x = – 7

(vii) __ ÷ (- 15) = 6
సాధన.
x ÷ (- 15) = 6 .. x = -3
x = 6 × (- 15)
a × (-b) = – (a × b) అని మనకు తెలుసు.
x = – (6 × 15)
∴ x = – 90

(viii) _____ ÷ (- 9) = 16
సాధన.
_x_ + (-9) = 16
x = 16 × (9)
a × (-b) = – (a × b) అని మనకు తెలుసు.
x = – (16 × 9)
∴ x = – 144

ప్రశ్న 3.
లబ్దము – 50 అయ్యే విధముగా వీలైనన్ని పూర్ణ సంఖ్యల జతలు వ్రాయండి.
సాధన.

ప్రశ్న 4.
పండ్ల వ్యాపారి శంకర్, 100 కి.గ్రా. కమలా పండ్లు మరియు 75 కి.గ్రా. దానిమ్మ పండ్లు అమ్మాడు. అతను ఒక కి.గ్రా. దానిమ్మ పండ్లపై ₹ 11 లాభాన్ని, ఒక కి.గ్రా. కమలా పండ్లపై ₹8 నష్టాన్ని పొందిన మొత్తము మీద అతనికి ఎంత లాభము లేదా నష్టము ?

సాధన.
పండ్ల వ్యాపారికి దానిమ్మ పండ్లపై కి.గ్రా. కు లాభం = ₹11
కావున, 75 కి.గ్రా. దానిమ్మ పండ్ల అమ్మకంపై లాభము = 75 × 11 = ₹ 825
కమలాపండ్లు అమ్మకంపై కి.గ్రా. కు నష్టం = – ₹8
100 కి.గ్రా. కమలాపండ్ల అమ్మకంపై నష్టం = 100 × (- 8) = – ₹800
వ్యాపారికి లాభం లేదా నష్టం = ₹825 + (- ₹800) = ₹ 25
∴ ₹25 ధన సంఖ్య కావున వ్యాపారికి ₹ 25 లాభం వస్తుంది.

ప్రశ్న 5.
భార్గవి జూన్ నెలలో యోగా ద్వా రా 5700 కేలరీలను తగ్గించుకొంది. కేలరీల తగ్గుదల స్థిరంగా వున్న, ఆ నెలలో రోజువారి సరాసరి కేలరీల తగ్గుదల ఎంత?

సాధన.
భార్గవి జూన్ నెలలో యోగా ద్వారా తగ్గిన కేలరీలు = – 5700
జూన్ నెలలోని రోజుల సంఖ్య = 30
జూన్ నెలలో రోజువారి సరాసరి కేలరీల తగ్గుదల
= (- 5700) ÷ 30

∴ సరాసరి కేలరీల తగ్గుదల = 190

ప్రశ్న 6.
625 × (- 35) + 625 × 30 ను తగిన న్యాయాలను ఉపయోగించి సూక్ష్మీకరించుము.
సాధన.
625 × (- 35) + 625 × 30
= 625 × [[- 35) + 30]
(సంకలనంపై గుణకార విభాగ న్యాయము)
= 625 × (- 5)
= – 3125

ప్రశ్న 7.
BODMAS ను ఉపయోగించి సూక్ష్మీకరించుము.
(i) 12 – 36 ÷ 3
సాధన. 1
2 – 36 ÷3 (భాగహారం)
= 12 – 12 (వ్యవకలనం)
= 0

(ii) 6 × (- 7) + (- 3) ÷ 3
సాధన.
6 × (- 7) + (-3) ÷ 3
= 6 × (- 7) + (- 1) (భాగహారం)
= (42) + (- 1) (గుణకారం)
= – 43 (సంకలనం)

(iii) 38 – {35 – (36 – \(\overline{34-37}\))}
సాధన.
38 – {35 – (36 – \(\overline{34-37}\)) }
= 38 – {35 – (36 + 3)} (విన్కులం)
= 38 – {35 – 39} (సాధారణ బ్రాకెట్)
= 38 + 4 (కర్లీ బ్రాకెట్)
= 42 (సంకలనం)

ప్రశ్న 8.
కింది సంఖ్యలకు పరమ మూల్య విలువను వ్రాయండి.
(i) – 700
సాధన.
|- 700| = 700

(ii) 150
సాధన.
|150| = 150

(iii) – 150
సాధన.
|- 150| = 150

(iv) – 35
సాధన.
|- 35| = 35

(v) p< 10 అయిన |p – 10|
సాధన.
p < 10 అయిన |p – 10|
= – (p – 10) = 10 – p

(vi) y > 7 అయిన |7 – y|
సాధన.
y > 7 అయిన |7 – y|
= – (7 – y) = y – 7
(y > 7 అయిన 7 – y < 0)

SCERT AP 7th Class Maths Solutions Pdf Chapter 1 పూర్ణ సంఖ్యలు Ex 1.4 Textbook Exercise Questions and Answers.

AP State Syllabus 7th Class Maths Solutions 1st Lesson పూర్ణ సంఖ్యలు Exercise 1.4

ప్రశ్న 1.
కింది వాటిని సూక్ష్మీకరించుము.
(i) 6 × 9 – 6 ÷ 3
సాధన.
6 × 9 – 6 ÷ 3
= 6 × 9 – 2 (భాగహారం)
= 54 – 2 (గుణకారం)
= 52 (వ్యవకలనం)

(ii) 12 ÷ 4 – 8 + 5
సాధన.
12 ÷ 4 – 8 + 5
= 3 – 8 + 5 (భాగహారం)
= 8 – 8 (సంకలనం)
= 0 (వ్యవకలనం)

(iii) 80 – 56 ÷ 8 × 9
సాధన.
80 – 56 ÷ 8 × 9
= 80 – 7 × 9 (భాగహారం)
= 80 – 63 (గుణకారం)
= 17 (వ్యవకలనం)

(iv) 15 ÷ 5 + 17 – 30
సాధన.
15 ÷ 5 + 17 – 30
= 3 + 17 – 30 (భాగహారం )
= 20 – 30 (సంకలనం)
= – 10 (వ్యవకలనం)

(v) 8 + 8 – 8 × 8 ÷ 8
సాధన.
8 + 8 – 8 × 8 ÷ 8
= 8 + 8 – 8 × 1 (భాగహారం )
= 8 + 8 – 8 (గుణకారం)
= 16 – 8 (సంకలనం)
= 8 (వ్యవకలనం)

ప్రశ్న 2.
కింది వాటిని సూక్ష్మీకరించుము.
i) 8 × 3 – \(\overline{13-7}\)
సాధన.
8 × 3 – \(\overline{13-7}\)
= 8 × 3 – 6 (విన్కులం)
= 24 – 6 (గుణకారం)
= 18 (వ్యవకలనం)

(ii) {12 – \(\overline{14-8}\) + 7} – 15
సాధన.
{12 – \(\overline{14-8}\) + 7} – 15
= {12 – 6+7} – 15 (విన్కులం)
= {19 – 6} – 15 (కర్లీ బ్రాకెట్లో సంకలనం)
= 13 – 15 (కర్లీ బ్రాకెట్ లో వ్యవకలనం)
= – 2 (వ్యవకలనం)

(iii) 16 – (4 + 18 ÷ 6 – \(\overline{7-5}\)) × 5
సాధన.
16 – (4 + 18 ÷ 6 – \(\overline{7-5}\)) × 5
= 16 – (4 + 18 ÷ 6 – 2) × 5(విన్కులం)
= 16 – (4 + 3 – 2) × 5 (భాగహారం)
= 16 – (7 – 2) × 5
= 16 – 5 × 5 (సాధారణ బ్రాకెట్)
= 16 – 25 (గుణకారం)
= – 9 (వ్యవకలనం)

(iv) {6 of 145 ÷ (3 + 2)} ÷ 2 – 4 of 20
సాధన.
{6 of 145 ÷ (3 + 2)} ÷ 2 – 4 of 20
= {6 of 145 ÷ 5} + 2 – 4 of 20 (సాధారణ బ్రాకెట్)
= {870 ÷ 5} ÷ 2 – 4 of 20 (ఆఫ్)
= 174 ÷ 2 – 4 of 20 (కర్లీ బ్రాకెట్)
= 174 + 2 – 80 (ఆఫ్)
= 87- 80 (భాగహారం)
= 7 (వ్యవకలనం)

(v) 25 + [14 – 18+ {12 of 5 -( 4 + 14)}]
సాధన.
25 + [14 – 18 + {12 of 5 -(-4 + 14)}]
= 25 + [14 – 18 + {12 of 5 – 10}] (సాధారణ బ్రాకెట్)
= 25 + [14 – 18 + {60 – 10}] (ఆఫ్ )
= 25 + [14 – 18 + 50] (కర్లీ బ్రాకెట్)
= 25 + [64 – 18]
= 25 + 46 (చతురస్ర బ్రాకెట్)
= 71 (సంకలనం)

ప్రశ్న 3.
కింది వాటిలో సత్య వాక్యాలను గుర్తించుము.
(i) 48 ÷ 6 – 4 = 24
సాధన.
48 ÷ 6 – 4 = 24
8 – 4 = 24 (భాగహారం)
4 ≠ 24 (వ్యవకలనం)
∴ అసత్యం

(ii) – 18 + 12 ÷ 3 = – 14
సాధన.
– 18 + 12 ÷ 3 = – 14
– 18 + 4 = – 14 (భాగహారం)
– 14 = – 14 (వ్యవకలనం)
∴ సత్యం

(iii) -11 + 3 ×7 = – 56
సాధన.
– 11 + 3 × 7 = – 56
-11 + 21 = – 56 (గుణకారం)
10 ≠ – 56 (వ్యవకలనం)
∴ అసత్యం

(iv) 2020 – 20 – 100 = 1
సాధన.
2020 + 20 – 100 = 1 (భాగహారం)
101 – 100 = 1 (వ్యవకలనం)
1 = 1
∴ సత్యం

ప్రశ్న 4.
కింది వాక్యాలు సత్యమయ్యే విధముగా ఖాళీలను +, -, ×, ÷ లతో పూరించుము.
(i) 9 __ 3 __ 6 = – 3
సాధన.
9 ÷ 3 – 6 = – 3

(ii) – 6 __ 12 __ 6 = – 4
సాధన.
– 6 + 12 ÷ 6 = -4

(iii) – 15 __ 3 __ 6 = – 30
సాధన.
– 15 ÷ 3 × 6 = – 30

SCERT AP 7th Class Maths Solutions Pdf Chapter 1 పూర్ణ సంఖ్యలు Ex 1.3 Textbook Exercise Questions and Answers.

AP State Syllabus 7th Class Maths Solutions 1st Lesson పూర్ణ సంఖ్యలు Exercise 1.3

ప్రశ్న 1.
కింది వాటిలో ఉన్న ధర్మాలను గుర్తించి రాయండి. విభాగ న్యాయమును పాటిస్తాయి.
(i) – 3 + 5 = 5 + (- 3)
సాధన.
– 3 + 5 = 5 + (- 3) సంకలన వినిమయ (స్థిత్యంతర) ధర్మము.

(ii) – 2 × 1 = 1 × (- 2) = – 2
సాధన.
(- 2) × 1 = 1 × (- 2) = – 2 గుణకార తత్సమ ధర్మము.

(iii) [[- 5) × 2] × 3 = (- 5) × [[2 × 3)]
సాధన.
[(- 5) × 2] × 3 = (- 5) × [(2 × 3)] గుణకార సహచర న్యాయము

(iv) 18 × [7 + (- 3)] = [18 × 7] + [18 × (-3)]
సాధన.
18 × [7 + (- 3)] = [18 × 7] + [18 × (- 3)] సంకలనం పై గుణకార విభాగ న్యాయము

(v) – 5 × 6 = – 30
సాధన.
(- 5) × 6 = – 30 గుణకార సంవృత ధర్మము

(vi) – 3 + 0 = 0 + (-3) = – 3
సాధన.
-3 + 0 = 0 + (-3) = – 3 సంకలన తత్సమ ధర్మము

ప్రశ్న 2.
కింది సందర్భాలలో లబ్దము యొక్క సంజ్ఞ (గుర్తు)ను రాయండి.
(i) ఋణ పూర్ణ సంఖ్యకు 24 రెట్లు
సాధన.
(- 1) × (- 1) ×…………… 24 రెట్లు = + 1 (ధనాత్మకం)

(ii) ఋణ పూర్ణ సంఖ్యకు 35 రెట్లు
సాధన.
(- 1) × (- 1) × ………………. 35 రెట్లు = – 1 (ఋణాత్మకం)

ప్రశ్న 3.
కింది ఖాళీల నందు సరైన పూర్ణ సంఖ్యలను తగిన న్యాయాల ఆధారంగా పూరించుము.
(i) – 3 + ________ = – 3.
సాధన.
– 3 + 0 = – 3

(ii) 2 × (- 3) = (- 3) × ________
సాధన.
2 × (- 3) = (- 3) × 2

(iii) – 6 + [3 + (- 2)] = [[- 6) + ________] + ________
సాధన.
– 6 + [3 + (-2)] = [(- 6) + 3 ] + (- 2)

(iv) – 6 × ________ = – 6
సాధన.
– 6 × 1 = – 6

(v) 5 × [[- 6) + 9] = ________ × (-6) + 5 × ________
సాధన.
5 × [(- 6) + 9] = 5 × (- 6) + 5 × 9

ప్రశ్న 4.
కింది వాక్యాలు సత్యమా ? అసత్యమా ? తెల్పండి. కారణాలు వ్రాయండి.
(i) 2 యొక్క గుణకార తత్సమాంశము – 2.
సాధన.
అసత్యం. 2 యొక్క గుణకార తత్సమాంశం \(\frac{1}{2}\).

(ii) పూర్ణ సంఖ్యలు వ్యవకలనము దృష్ట్యా వినిమయ న్యాయము పాటిస్తాయి.
సాధన.
అసత్యం . (-5) – 3 ≠ 3 – (-5)

(iii) a మరియు bలు ఏవైనా రెండు పూర్ణ సంఖ్యలు అయిన a × b = b × a.
సాధన.
సత్యం .
4 × (-5) = (- 5) × 4 .
-(4 × 5) = – (5 × 4)
– 20 = -20
పూర్ణ సంఖ్యలు గుణకార వినిమయ ధర్మాన్ని పాటిస్తాయి.

(iv) సున్నాతో పూర్ణసంఖ్యల భాగహారము నిర్వచించబడదు.
సాధన.
సత్యం
6 ÷ 0 (సాధ్యం కాదు)

(v) 6 + (-6) = (-6) + 6 = 0 అనునది సంకలన తత్సమ ధర్మమును సూచించును.
సాధన.
అసత్యం.
6 + (-6) = (-6) + 6 = 0 అనునది సంకలన విలోమ ధర్మము.

ప్రశ్న 5.
కింది వాటిని తగిన న్యాయాలనుపయోగించి సూక్ష్మీ కరించుము.
(i) – 11 × ( 25) × (- 4)
సాధన.
– 11 × (- 25) × (4)
a × (b × c)
= (- 11) × [[- 25) × (- 4)]
= (- 11) × (25 × 4)
= – 11 × 100
= – (11 × 100)
= – 1100

(ii) 3× (- 18) + 3 × (- 32)
సాధన.
3 × (- 18) + 3 × (- 32)
(a × b) + (a × c) = a × (b + c)
= 3 × [[- 18) + (- 32)]
= 3 × (- 18 – 32)
= 3 × (- 50)
= – (3 × 50)
= – 150

ప్రశ్న 6.
పూర్ణ సంఖ్యలు వ్యవకలనము దృష్ట్యా సహచర న్యాయమును పాటిస్తాయా ? ఉదాహరణ ద్వారా వివరించుము.
సాధన.
పాటించవు.
మూడు పూర్ణసంఖ్యలు a = 2, b = -3, c = 5 అనుకొందాం.
(i) (a – b) – c = [2 – (-3)] – (5)
= (2 + 3) – 5 = 5 – 5 = 0

(ii), a – (b – c) = 2 – [[-3) – (5)] = 2 – [- 3 – 5]
= 2 – (- 8) = 2 + 8 = 10
(a – b) – c ≠ a – (b – c)
∴ [2 – (-3)] – (5) ≠ 2 – [[-3) – (5)]
కావున, పూర్ణసంఖ్యలు వ్యవకలనం దృష్ట్యా సహచర న్యాయమును పాటించవు.

ప్రశ్న 7.
[(-5) × 2] × 3 = (-5) × [[2 × 3)] సరిచూడుము.
సాధన.
[(-5) × 2)] × 3 = (-5) × [(2 × 3)]
(a× b) × c = a × (b × c)
(- 10) × 3 = (-5) × 6
– 30 = – 30
∴ పూర్ణసంఖ్యలు గుణకారము దృష్ట్యా సహచర న్యాయమును పాటిస్తాయి.

SCERT AP 7th Class Maths Solutions Pdf Chapter 1 పూర్ణ సంఖ్యలు Ex 1.2 Textbook Exercise Questions and Answers.

AP State Syllabus 7th Class Maths Solutions 1st Lesson పూర్ణ సంఖ్యలు Exercise 1.2

ప్రశ్న 1.
క్రింది వాటిని లెక్కించండి.
(i) (- 96) ÷ 16
సాధన.
(-96) ÷ 16 = – 6

(ii) 98 ÷ (- 49)
సాధన.
98 ÷ (- 49) = – 2

(iii) (- 51) ÷ 17.
సాధన.
(- 51) ÷ 17 = – 3

(iv) 38 ÷ (- 19)
సాధన.
38 ÷ (- 19) = – 2

(v) (- 80) ÷ 20
సాధన.
(- 80) ÷ 20 = – 4.

(vi) (- 150) ÷ (- 25)
సాధన.
(- 150) ÷ (- 25) = 6

(vii) (- 600) ÷ 60
సాధన.
(- 600) ÷ 60 = – 10

(viii) (- 54) ÷9
సాధన.
(- 54) ÷ 9 = – 6

(ix) 130 ÷ 65
సాధన.
130 ÷ 65 = 2

(x) (- 315) ÷ (- 315)
సాధన.
(- 315) ÷ (- 315) = 1

ప్రశ్న 2.
రెండు పూర్ణ సంఖ్యల లబ్దము – 165. అందులో ఒక సంఖ్య -15 అయిన రెండవ సంఖ్య కనుగొనుము.
సాధన.
రెండు పూర్ణ సంఖ్యల లబ్దము = -165
అందులో ఒక సంఖ్య = -15
రెండవ సంఖ్య = (-165) + (-15)

∴ రెండవ సంఖ్య = 11

ప్రశ్న 3.
2020 సం||లో కోవిడ్-19 వలన ఒక కంపెనీ 6 నెలలు లాక్ డౌన్ లో వుండినది మరియు ₹ 1,32,000 నష్టపోయినది. నెలసరి సరాసరి నష్టమును కనుగొనుము.

సాధన.
6 నెలల లాక్ డౌన్ సమయంలో వచ్చిన నష్టము = ₹(- 1,32,000)
నెలసరి సరాసరి నష్టము = – 1,32,000 ÷ 6
= \(\frac{-1,32,000}{6}\) = ₹ – 22,000
∴ ప్రతినెల సరాసరి ₹ 22,000 నష్టం వచ్చినది.

ప్రశ్న 4.
మధ్యాహ్నం 12 గంటలకు ఉష్ణోగ్రత 0° పైన 10°C అని గుర్తించబడినది. ఉష్ణోగ్రత ప్రతి గంటకు 2°C చొప్పున అర్ధరాత్రి వరకు తగ్గుతుంది. ఏ సమయానికి 0° కన్నా 8°C తక్కువగా ఉంటుంది ? అర్ధరాత్రి ఉష్ణోగ్రత ఎంత ?
సాధన.
మధ్యాహ్నం 12 గంటలకు ఉష్ణోగ్రత = + 10°C
ప్రతి గంటకు తగ్గుతున్న ఉష్ణోగ్రత = – 2°C
0° కన్నా 8°C తక్కువగా ఉండుటకు (- 8°C) అవుటకు తగ్గవలసిన ఉష్ణోగ్రత = (-8) – (10) = – 18°C
– 18°C ఉష్ణోగ్రత తగ్గుటకు పట్టుకాలము = -18 + (-2) = 9 గంటలు
∴ రాత్రి 9 గంటలకు 0° కన్నా 8°C తక్కువగా ఉంటుంది.
∴ అర్ధరాత్రి ఉష్ణోగ్రత = (- 8°C) + (- 2°C × 3 గంటలు) = (- 8°C + – 6°C) = – 14°C

ప్రశ్న 5.
ఒక కూరగాయల వ్యాపారి ఒక కి.గ్రా. టమోటాపై ₹7 లాభముతో, ఒక కి.గ్రా. వంకాయలపై ₹ 4 నష్టముతో అమ్మాడు. అతను సోమవారము 68 కి.గ్రా.ల టమోటాలు అమ్మినా లాభము కానీ నష్టము కానీ రాలేదు. అయిన అతను ఆ రోజు ఎన్ని కి.గ్రా.ల వంకాయలు అమ్మాడు?

సాధన.
కూరగాయల వ్యాపారికి ఒక కి.గ్రా. టమోటాపై వచ్చు లాభము = ₹7
1 కి.గ్రా. వంకాయలపై వచ్చు నష్టము = ₹(4)
వ్యాపారి అమ్మిన టమోటాలు = 68 కి.గ్రా.
టమోటా కిలోల సంఖ్య = x కి.గ్రా. అనుకొనుము
వంకాయలు కిలోల సంఖ్య = y కి.గ్రా. అనుకొనుము
7x – 4y = 0
⇒ 7 × 68 – 4y = 0
⇒ – 4y = – 7 × 68
⇒ y = \(\frac{-7 \times 68}{-4}\)
∴ ఆ రోజు వ్యాపారి అమ్మవలసిన వంకాయలు
= + 7 × 17 = + 119 కిలోలు.

ప్రశ్న 6.
ఒక పరీక్షలో, ప్రతి సరైన సమాధానానికి + 3 మార్కులు మరియు ప్రతి తప్పుకు -1 మార్కులు ఇవ్వబడతాయి. సోనా అన్ని ప్రశ్నలకు సమాధానాలు వ్రాయగా, అందులో 10 సరియైనవి మరియు ఆమె 20 మార్కులు పొందినది.
(i) ఆమె రాసిన తప్పు సమాధానాలు ఎన్ని ?
సాధన.
ప్రతి సరైన సమాధానానికి మార్కులు = + 3 .
కావున, 10 సరైన సమాధానాలకు మార్కులు = 10 × 3 = 30
ఇవ్వబడిన లెక్క ప్రకారం, సోనాకు వచ్చిన మార్కులు = 20
తప్పు సమాధానాలకు మార్కులు = 20 – 30 = – 10
ప్రతి తప్పు సమాధానానికి మార్కులు = – 1
∴ తప్పు సమాధానాలు రాసిన ప్రశ్నల సంఖ్య = (- 10) ÷ (- 1) = 10

(ii) పరీక్షలో ఇవ్వబడిన మొత్తం ప్రశ్నలు ఎన్ని ?
సాధన.
పరీక్షలోని మొత్తం ప్రశ్నల సంఖ్య = సరైన సమాధానాలు రాసిన ప్రశ్నలు + తప్పు సమాధానం రాసిన ప్రశ్నలు
= 10 + 10 = 20

ప్రశ్న 7.
a ÷ b = – 4 అగునట్లు 5 పూర్ణ సంఖ్యల జత (a, b) లు వ్రాయుము.
(ఉదా: (12, – 3) ఎందుకనగా 12 ÷ (- 3) = – 4).
సాధన.
(i) (16, – 4)
(ii) (- 48, 12)
(iii) (40, – 10)
(iv) (- 64, 16)

SCERT AP 7th Class Maths Solutions Pdf Chapter 1 పూర్ణ సంఖ్యలు Ex 1.1 Textbook Exercise Questions and Answers.

AP State Syllabus 7th Class Maths Solutions 1st Lesson పూర్ణ సంఖ్యలు Exercise 1.1

ప్రశ్న 1.
కింది వాటిని గుణించండి.
(i) 5 × 7
సాధన.
5 × 7 = 35

(ii) (-9) × (6)
సాధన.
(-9) × 6 = – 54

(iii) (9) × (- 4)
సాధన.
9 × (4) = – 36

(iv) (8) × (-7)
సాధన.
8 × (-7) = – 56

(v) (-124) × (-1)
సాధన.
(-124) × (-1) = + 124

(vi) (-12) × (-7)
సాధన.
(-12) × (-7) = + 84

(vii) (- 63) × 7,
సాధన.
(- 63) × 7 = – 441

(viii) 7 × (- 15)
సాధన.
7 × (- 15) = – 105

ప్రశ్న 2.
కింది వాటిలో పెద్దది ఏది ?
(i) 2 × (- 5) లేదా 3 × (-4)
సాధన.
2 × (- 5) లేదా 3 × (4)
– (2 × 5) = – 10, – (3 × 4) = – 12
– 10 > – 12
∴ 2 × (-5) పెద్దది

(ii) (- 6) × (- 7) లేదా (-8) × 5
సాధన.
(- 6) × (- 7) లేదా (-8) × 5
+ (6 × 7) = 42, – (8 × 5) = – 40
42 > – 40
∴ (- 6) × (- 7) పెద్దది

(iii) (- 6) × 10 లేదా (-3) × (- 21)
సాధన.
(- 6) × 10 లేదా (-3) × (-21).
– (6 × 10) = – 60, + (3 × 21) = 63
63 > – 60
∴ (- 3) × (- 21) పెద్దది

(iv) 9 × (- 11) లేదా 6 × (- 16)
సాధన.
9 × (-11) లేదా 6 × (-16)
– (9 × 11) = – 99, – (6 × 16) = – 96
– 96 > – 99
∴ 6 × (-16) పెద్దది

(v) (- 8) × (- 5) లేదా (-9) × (-4)
సాధన.
(- 8) × (- 5) లేదా (-9) × (4)
+ (8 × 5) = 40, + (9 × 4) = 36
40 > 36
∴ (- 8) × (-5) పెద్దది

ప్రశ్న 3.
రెండు పూర్ణసంఖ్యల లబ్దము i) ఒక ధన పూర్ణ సంఖ్య ii) ఒక రుణ పూర్ణ సంఖ్య iii) సున్నా అగునట్లు పూర్ణ సంఖ్యలను వ్రాయుము.
సాధన.
లబ్దము (i) ఒక ధన పూర్ణ సంఖ్య:
(i) 4 × 3
(ii) (+ 4) × (- 3)
(iii) (- 10) × (- 5)

లబ్దము (ii) ఒక రుణ పూర్ణ సంఖ్య:
(i) (4) × 3
(ii) 4 × (-3)
(iii) (- 10) × 5

లబ్దము (iii) సున్న:
(i) 0 × 5
(ii) (- 5) × 0
(iii) 0 × 0

ప్రశ్న 4.
ఒక కప్ప నిముషానికి 3 మీటర్ల వంతున బావి పై ఉపరితలం నుండి లోపలికి జారుతున్నది. కప్ప 5 నిముషాల తరువాత బావిలో ఏ స్థానములో ఉంటుంది?

సాధన.
కప్ప నిముషానికి బావి లోపలికి జారుతున్న లోతు = -3 మీటర్లు
5 నిముషాలలో కప్ప జారు లోతు = 5 × (-3) = -15 మీటర్లు
∴ 5 నిమిషాల తరువాత కప్ప బావి ఉపరితలం నుండి 15 మీటర్ల లోతులో ఉంటుంది.

ప్రశ్న 5.
వేసవిలో ఒక కొలనులో నీటిమట్టము బాష్పీభవనం వలన ఒక వారానికి 5 అంగుళాల చొప్పున తగ్గుతున్నది. నీటి స్థాయి స్థిర పరిమాణములో తగ్గుచున్నచో, 6 వారాల తరువాత కొలనులో నీటి మట్టములో మార్పు ఎంత ఉండును?

సాధన.
బాష్పీభవనం వలన ఒక వారానికి తగ్గు నీటి మట్టము = – 5 అంగుళాలు
6 వారాల తరువాత కొలనులో నీటి మట్టంలో మార్పు = 6 × (- 5) = -30 అంగుళాలు
∴ 6 వారాల తరువాత నీటి మట్టం 30 అంగుళాలు తగ్గుతుంది.

ప్రశ్న 6.
ఒక దుకాణదారుడు ఒక్కొక్క పుస్తకం అమ్మడం వలన ₹5లు లాభాన్ని మరియు ఒక్కొక్క పెన్ను అమ్మడం వలన ₹3లు నష్టము పొందును. జూలై నెలలో అతను 1500 పుస్తకాలు మరియు 1500 పెన్నులు అమ్మిన అతనికి వచ్చిన లాభము లేదా నష్టమును కనుగొనుము.
సాధన.
ఒక్కొక్క పుస్తకం అమ్మడం వలన దుకాణదారునకు వచ్చు లాభము = ₹5
1500 పుస్తకాలు అమ్మడం వలన వచ్చు లాభం = 1500 × 5 = ₹7500
ఒక్కొక్క పెన్ను అమ్మడం వలన దుకాణదారునకు వచ్చు నష్టం = ₹(-3)
1500 పెన్నులు అమ్మడం వలన వచ్చు నష్టం = 1500 × (-3) = ₹ – 4500
1500 పుస్తకాలు, 1500 పెన్నులు అమ్మడం వలన వచ్చు లాభము లేదా నష్టము = 7500 + (- 4500) = ₹3000
ఫలితం ధన సంఖ్య కావున ₹ 3000 లాభం వస్తుంది.

ప్రశ్న 7.
ఒక సిమెంటు కంపెనీ ఒక్కొక్క తెలుపు రంగు బస్తా సిమెంటుపై ₹8 లాభం మరియు బూడిద రంగు బస్తా సిమెంటుపై ₹6 నష్టముతో అమ్మింది. ఒక నెలలో 2,000 బస్తాల తెలుపు రంగు సిమెంటు, 3,000 బస్తాల బూడిద రంగు సిమెంటు అమ్మిన దానికి వచ్చినది లాభమా లేదా నష్టమా ఏమిటో కనుగొనండి.
సాధన.
సిమెంటు కంపెనీకి ఒక్కొక్క తెలుపు రంగు సిమెంటు బస్తాపై వచ్చు లాభము = ₹8
2000 తెలుపు రంగు సిమెంటు బస్తాలపై వచ్చు లాభము = 2000 × 8 = ₹ 16,000
సిమెంటు కంపెనీకి ఒక్కొక్క బూడిదరంగు సిమెంటు బస్తాపై వచ్చు నష్టము = ₹ (- 6)
3,000 బూడిద రంగు సిమెంటు బస్తాలపై వచ్చు నష్టము = 3000 × (- 6) = ₹ – 18000
2,000 బస్తాల తెలుపు రంగు సిమెంట్, 3000 బస్తాల బూడిద రంగు సిమెంట్ అమ్మడం వలన వచ్చు లాభం లేదా నష్టము = (16000) + (-18000) = ₹ – 2000
∴ ఫలితం రుణసంఖ్య కావున ₹ 2000 నష్టం వస్తుంది.

ప్రశ్న 8.
ప్రవచనం సరియగునట్లు కింది ఖాళీలను సరైన పూర్ణ సంఖ్యచే పూరించుము.
(i) (-4) ×________ = – 20
సాధన.
(- 4) × 5 = – 20

(ii) ________ × 5 = – 35
సాధన.
(- 7) × 5 = – 35

(iii) (-6) × ________ = 48
సాధన.
(- 6) × (-8) = 48

(iv) ________ × (-9) = 45
సాధన.
(5) × (-9) = 45

(v) ________ × 1 = – 42
సాధన.
(-6) × 7 = – 42

(vi) 8 × ________ = – 8
సాధన.
8 × (- 1) = – 8

SCERT AP 7th Class Maths Solutions Pdf Chapter 1 పూర్ణ సంఖ్యలు Review Exercise Questions and Answers.

AP State Syllabus 7th Class Maths Solutions 1st Lesson పూర్ణ సంఖ్యలు Review Exercise

ప్రశ్న1.
కింది వాక్యాలను సరైన పూర్ణ సంఖ్యతో సూచించండి.
(i) స్నేహ తన పొదుపు ఖాతాలో ₹2000 జమ చేసినది.
సాధన.
+ ₹ 2000

(ii) జలాంతర్గామి సముద్ర మట్టము నుండి 350 అడుగుల లోతులో ఉంది.
సాధన.
– 350 అడుగులు

(iii) ఎవరెస్టు శిఖరం సముద్ర మట్టము నుండి 8848 మీ. ఎత్తులో ఉంది.
సాధన.
+ 8848 మీ.

(iv) 0°C కన్నా 14 డిగ్రీల తక్కువ ఉష్ణోగ్రత ఉంది.
సాధన.
– 14°C

ప్రశ్న2.
క్రింది సంఖ్యారేఖపై లేని పూర్ణసంఖ్యలను గుర్తించండి.

సాధన.

ప్రశ్న3.
క్రింది పూర్ణ సంఖ్యలను అవరోహణ మరియు ఆరోహణ క్రమంలో వ్రాయండి.

(i) -9, -1, 0, – 10, -6
సాధన.
అవరోహణ క్రమం: 0, -1, -6, -9, -10
ఆరోహణ క్రమం: -10, -9, -6, -1, 0

(ii) -6, 6, -9, 5, 10, -3
సాధన.
అవరోహణ క్రమం: 10, 6, 5, -3, -6, -9
ఆరోహణ క్రమం: -9, -6, -3, 5, 6, 10

(iii) -15, -20, -35, 0, 2
సాధన.
అవరోహణ క్రమం: 2, 0, -15, -20, -35
ఆరోహణ క్రమం: -35, -20, -15, 0, 2

ప్రశ్న4.
క్రింది వాటిని లెక్కించుము.
(i) – 2 + 3
సాధన.
– 2 + 3 = + 1

(ii) -6 + (-2)
సాధన.
– 6 + (-2) = – 8

(iii) 8 – (-6)
సాధన.
8 – (-6) = 8 + 6 = + 14

(iv) -9 + 4
సాధన.
-9 + 4 = -5

(v) – 23 – (-30)
సాధన.
– 23 – (-30) = – 23 + 30 = + 7

(vi) 50 – 153
సాధన.
50 – 153 = – 103

(vii) 71 + (-10) – 8
సాధన.
71 + (-10) – 8 = 71 + (-18) = + 53

(viii) – 30 + 58 – 38
సాధన.
– 30 + 58 – 38 = – 68 + 58 = – 10

ప్రశ్న5.
సియాచిన్ వద్ద 5 a.m ఉష్ణోగ్రత 0°C కన్నా 10°C తక్కువ ఉంది. ఆరు గంటల తర్వాత అది 14°C పెరిగినది. 11 a.m వద్ద ఉష్ణోగ్రత ఎంత ఉంటుంది?

సాధన.
సియాచిన్ వద్ద 5 a.m ఉష్ణోగ్రత = – 10°C
ఆరు గంటల తర్వాత పెరిగిన ఉష్ణోగ్రత = + 14°C
∴ 11 a.m వద్ద ఉష్ణోగ్రత = (-10) + 14 = + 4°C

ప్రశ్న6.
ఒక చేప సముద్ర ఉపరితలం నుండి 16 అడుగుల లోతులో ఉంది మరియు మరొక 17 అడుగుల కిందకు వెళ్ళింది. ప్రస్తుతం సముద్ర మట్టం నుండి చేప స్థానం ఏమిటి ?
సాధన.
సముద్రమట్టం నుండి మొదట చేపగల స్థానం = -16 అడుగులు
చేప మరొక 17 అడుగులు క్రిందకు వెళితే చేప ప్రస్తుత స్థానం = (-16) + (-17) = – 33 అడుగులు
అనగా చేప ప్రస్తుతం సముద్ర మట్టం నుండి 33 అడుగుల లోతులో ఉంటుంది.

ప్రశ్న7.
ఒక ఆకుకూరల వ్యాపారి సోమవారం నాడు ₹250 లాభం, మంగళవారం నాడు ₹ 120 నష్టం మరియు బుధవారం నాడు ₹180 నష్టం పొందాడు. మూడు రోజుల తరువాత వచ్చిన మొత్తం లాభం లేదా నష్టం ఎంతో కనుగొనుము.
సాధన.
ఆకుకూరల వ్యాపారికి
సోమవారం లాభం = ₹250
మంగళవారం నష్టం = ₹120
బుధవారం నష్టం = ₹180
∴ మూడు రోజుల తర్వాత వచ్చిన మొత్తం లాభం లేదా నష్టం = + 250 + (-120) + (-180)
= 250 + (-300) = -50
∴ వ్యాపారికి మూడు రోజుల తరువాత ₹ 50 నష్టం వస్తుంది.

ప్రశ్న8.
మొదటి పటంలో రెండు పూర్ణసంఖ్యల యొక్క సంకలనం ఆధారంగా మరియు రెండో పటంలో రెండు పూర్ణసంఖ్యల వ్యవకలనం ఆధారంగా పూర్తి చేయుము.

పాదన.

SCERT AP 7th Class Science Study Material Pdf 11th Lesson Soil and Water Textbook Questions and Answers.

AP State Syllabus 7th Class Science 12th Lesson Questions and Answers Soil and Water

7th Class Science 12th Lesson Soil and Water Textbook Questions and Answers

Improve Your Learning

I. Fill in the blanks.

1. Wastewater released from houses is called _______.
2. The Science dealing with the formation of soil is called _______.
3. In modern water purifiers _______ are used instead of chlorine to kill the germs.
Answer:
1. Sewage
2. Pedology
3. Ultraviolet rays

II. Choose the correct answer.

1. In addition to the soil particles, the soil also has
a) air and water
b) water and plants
c) minerals, organic matter, air and water
d) water, air and plants
Answer:
c) minerals, organic matter, air and water

2. The water holding capacity is the highest in
a) sandy soil
b) clayey soil
c) loamy soil
d) mixture of sand and loam
Answer:
b) clayey soil

3. Which among the following is not responsible for water shortage?
a) Industrial growth
b) Population growth
c) Heavy rainfall
d) Mismanagement of water resources
Answer:
c) Heavy rainfall

III. Matching.

Answer:

IV. Answer the following questions

Question 1.
Explain briefly the terms.
i) Weathering ii) Aquifer iii) Percolation iv) Sewage
Answer:
i) Weathering :

1. In nature due to the action of various natural agents such as wind, water, sun and climate the bigger rocks (parent rock) gradually breakdown and give small particles. These form the soil. This process is known as Weathering.
2. It takes approximately 500 -1000 years for the formation of 1 inch of soil.
3. Weathering helps in the formation of soil.
4. The process of formation of soil from the parent rock by the process of weathering is called ‘Pedogenesis’.

ii) Aquifer :

1. Ground water is stored between layers of hard rock below the water table. This is called aquifer.
2. The wells, tube wells and hand pumps get water present in the aquifer.

iii) Percolation :

1. The absorption and downward movement of water through the soil layer is called percolation.
2. The rate of percolation various from soil to soil.
3. Sandy soils are well aerated and they have high percolation rate.

iv) Sewage :

1. All the waste water released by homes, industries, hospitals, offices and other users are collectively called sewage.
2. Sewage is a liquid waste.
3. Sewage contain water with dissolved and suspended impurities, disease causing bacteria and other microbes. These impurities are called contaminants.
4. Discharge of untreated sewage into canals causes harm to aquatic life.

Question 2.
List the differences between clayey soil, loamy soil and sandy soil. How is clayey soil useful for crops?
Answer:

1. Clayey soils are less aerated and their water holding capacity is higher.
2. It has finer particles less than 0.002 mm. Hence, they retain the water for a longer period.
3. Clayey soils are very suitable to grow crops like paddy. Sugarcane and cotton. Black soil with highest clay are suitable to grow crops like redgram. chillies etc.

Question 3.
Harshith observed that majority of the houses in his locality get water through bore well but no house has taken measures for rain water harvesting. Guess the long term effect on the water table.
Answer:

1. Over use of ground water can cause wells to dry up.
2. This leads to expensive and ultimately fertile attempts to keep up with the dropping water table by drilling deeper and deeper wells.
3. People will have to travel for miles to get water for their daily use.
4. People will migrate to longer distances in search of drinking water and villages would become barren.

Question 4.
If you get a chance to interview a soil scientist, what questions will you ask related to soil, its testing and conservation.
Answer:
I shall ask the following questions.

1. How can you test the soil for its acidity?
2. Is it possible to change the basic nature of the soil?
3. How can the water holding capacity of the soil be increased at a low cost?
4. Suggest methods to improve the fertility of the soil.
5. What can be done with the black cotton soil when a building is to be constructed?
6. As black cotton soil yields, and the building cracks, suggest preventive measures for it.

Question 5.
Your friends conducted an experiment in the field regarding the rate of percolation. They observed that it took 40 min for 200 ml of water to percolate through the soil. Calculate the rate of percolation. Also write the procedure to conduct the test.
Answer:

Procedure :

1. Take a soil sample.
2. Take a plastic funnel and place a filter paper in it as shown in the figure.
3. Weigh 50 gms of dry soil and pour it into the funnel.
4. Take 200 ml of water in a measuring cylinder.
5. Then pour the water on the soil drop by drop.
6. Pour the water all over the surface of the soil until it starts dripping out of the funnel. Calculate the time taken for the last water drop passes down the soil.

Question 6.
We call earth as “Bhoomatha -The Mother Earth”. How do you express your appreciation and gratitude to her?
Answer:

1. Soil is one of the most important natural resources. It supports the existence of living organisms.
2. We use soil for different purpose in our daily life. Almost all living things in our surroundings directly or indirectly depend on soil.
3. The soil supports all plants, animals and micro organisms.
4. We grow our food components in this soil.
5. Soil is the birth place of all minerals, everything we get from this soil. Hence, we consider the earth as “Bhoomatha – The Mother Earth”.

Question 7.
Poorvika wants to maintain a garden,- what suggestions can you give her to minimize the use of water and also to improve the soil quality?
Answer:

1. By using sprinklers and drip irrigation methods we can reduce the wastage of water in the garden.
2. Construction of soaking pits in the garden enhances the percolation of raia water into the soil. It improves the ground water table.
3. Rotting vegetation and animal remains make up the humus rich in fertility.
4. They contain nutrients, natural manure, which give good support to the growth of ‘ plants.
5. I also suggest Poorvika to grow big trees around the garden to stop winds.
6. It is better to grow grass and other plants in the vacant portions of the garden. These grass plant roots hold the solid particles and prevent soil erosion during heavy rains.

7th Class Science 12th Lesson Soil and Water InText Questions and Answers

7th Class Science Textbook Page No. 84

Question 1.
Where do animals and humans live?
Answer:
They live on the Earth.

Question 2.
What would happen if there is no soil on the Earth?
Answer:
Life on the earth would become impossible.

Question 3.
Why is woman in the picture using hand pump?
Answer:
For getting drinking water.

Question 4.
Why is soil an important resource?
Answer:
It is the important natural resources necessary for life on the earth. Human beings, plants and micro organisms depend on soil for their basic needs.

Question 5.
Where do plants get nutrients from?
Answer:
From soil.

Question 6.
Did you ever see earthworms and snails coming out of soil during rainy season?
Answer:
Yes, they live in the soil by making burrows.

7th Class Science Textbook Page No. 85

Question 7.
Is soil useful to us in any other way?
Answer:
Yes, soil is also needed.

1. For agriculture
2. For constructing buildings
3. For making toys and idols
4. For making utensils and pottery
5. For making cosmetics (multani soil)

Question 8.
Did you observe stones of different sizes at the bank of a stream?
Answer:
Yes. I observed many stones with different sizes and shapes.

Question 9.
What happens when rocks get rubbed and scroll due to the flow of water?
Answer:
Weathering of rocks takes place.

Question 10.
You might have observed white coloured crinkles on the rocks at the bank of river. How do they appear?
Answer:
They appear like shining jewels. They are formed by the disintegration of rock due to the abarsion of water stream.

Question 11.
Have you observed the top soil in your surroundings? What is it made of?
Answer:
Yes. It is made of dead and decayed organic matter called Humus.

7th Class Science Textbook Page No. 86

Question 12.
What do you observe floating on the top?
Answer:
Humus.

Question 13.
What do you find at the bottom of the beaker?
Answer:
Inorganic matter of the soil.

Question 14.
Do you find any insects and plant parts in the beaker?
Answer:
Yes, they are floating. It is the organic matter of the soil.

Question 15.
What do you infer from your observation?
Answer:
We can infer that soil consists of water, air, organic matter, inorganic matter and organisms.

Question 16.
How many layers did you observe in the pit?
Answer:
Two layers can be observed in the pit.

Question 17.
Do all the layers have same colour, texture and depth?
Answer:
No, all the layers have different colour, texture and depth.

7th Class Science Textbook Page No. 87

Question 18.
How can you identify which soil is suitable for this purpose?
Answer:
Clayey soil is suitable for making Ganesh idol.

7th Class Science Textbook Page No. 88

Question 19.
Do all types of soils have same properties?
Answer:
No, they have different properties.

7th Class Science Textbook Page No. 89

Question 20.
What type of soils are generally seen in our state?
Answer:
Sandy soils, black soils, red soils, loamy soils are seen in our state.

Question 21.
Can we grow a crop in all types of soil?
Answer:
No, it is not possible.

Question 22.
What type of soil is required for growing paddy?
Answer:
Paddy is grown in clayey soil, which retains water for a longer period.

Question 23.
Is there any relationship between the crops and soil?
Answer:
Yes, all crops are not grown in all soils. Crops are soil specific. For example cashew is grown in sandy soils and cotton is grown in black soils.

7th Class Science Textbook Page No. 90

Question 24.
Why is soil testing done?
Answer:
It helps a farmer to make a soil suitable for growing crops.

Question 25.
How do the farmers benefit by soil testing?
Answer:

1. Soil testing helps the farmer to know about the current health of the farm’s soil and how to improve it.
2. It helps farmers to prevent the degradation of soil quality.
3. It helps to minimize usage of fertilizers.

Question 26.
Did you observe that after heavy rain, the top soil get washed off?
Answer:
Yes. I observed it during rainy season.

Question 27.
What will happen if the top soil is washed off?
Answer:
The soil will loose its quality and fertility.

Question 28.
How can we prevent it?
Answer:

1. By afforestation. Controlling the deforestation activities.
2. Constructing checkdams and bunds
3. Preventing over grazing of land by animals.
4. By planting trees as shelter belt to stop winds. .
5. By planned agricultural practices we can prevent soil erosion successfully.

7th Class Science Textbook Page No. 91

Question 29.
What are the other causes of soil erosion?
Answer:

1. Unplanned and excessive usage of agro chemicals
2. Over grazing of land
3. Deforestation
4. Digging the earth for construction and mining

7th Class Science Textbook Page No. 92

Question 30.
Is water from seas and oceans useful for drinking and agriculture?
Answer:
No, the sea water is not useful for drinking and agriculture. But by desalinating the sea water we can use them for consumption.

Question 31.
Where is fresh water available from?
Answer:
From rivers, lakes, streams and ravines.

Question 32.
How much percentage of fresh water is available?
Answer:
only 1%.

Question 33.
How does the water reach the ground?
Answer:
The water reach the ground by infiltration.

Question 34.
Is the water table level same at all places?
Answer:
No, it is always vary in different places.

7th Class Science Textbook Page No. 93

Question 35.
Why do wells dry up?
Answer:
Decrease in ground water table leads to dry up of wells.

Question 36.
What will happen if the ground water table go down?
Answer:
All the wells and bore wells will dry up.

7th Class Science Textbook Page No. 94

Question 37.
Why is it essential to manage the water?
Answer:
To resolve the prevailing water scarcity in the society, proper water management of water resources is very essential.

Think & Respond

Question 1.
You may come across some people breaking large rocks into smaller ones to make road. Is it also the weathering of rocks? Why?
Answer:

1. In natural weathering process, the parent rock is gradually breakdown into small particles by the action of air, water, sun heat, and climate. It takes 500 to 1000 years times. This helps in formation of soil.
2. The break do\yn of rocks for the purpose of constructing roads and buildings also comes under weathering.

Here, the big rocks are blown down by using dynamites. In very short time, the bigger rocks become small gravel. It is artificial weathering or man made weathering. But this will not help in the formation of soil. This leads to the rapid depletion of natural resources like hills and mounds. The natural weathering factors like wind, water, sun have no role in this artificial weathering.

Question 2.
There is huge amount of water on earth, then why is water called a precious resource?
Answer:

1. About 97% of water is present in seas and oceans which is not useful for drinking and agriculture.
2. 2% of water is present in the form of rain, snow, sleet and precipitated water which is not available for consumption.
3. Hence only 1% of fresh water is available in the form of surface and ground water sources. This 1% of water is useful for drinking, domestic usage and agriculture.
4. Hence, we have to use this 1% of fresh water wisely and judiciously. This water is basis of life and human civilization. So, water is life. Save water save lives.
5. So, we considered water as a precious resource.

Activities and Projects

Question 1.
Under the guidance of your teacher collect the wet waste from Mid Day Meal preparation and make Vermi compost for your school garden.
Answer:

1. With the help of my science teacher, we constructed 10 × 1 × 1/2 meters Vermi Compost beds in sheds which protect these beds from direct sunlight and rain.
2. We collected coconut, banana and sugarcane leaves. We made them into 3- 4 inches layer. This inner layer was wet with water.
3. We collected the wet waste from Mid Day Meal to fill the bed. We were careful to avoid glass, polythlene, rubber and metal objects in the bed.
4. After two weeks of making bed we kept thousand earth worms per square meter and covered the bed with Gunny bags to maintain 30 to 40% of moisture.
5. After 60 days we collected the first manure. Second time we got the manure with in 40 – 50 days.
6. By using this Vermi Compost we can reduce the investments on chemical fertilizers and other pesticides. The quality of the soil and agricultural produce increased.

Question 2.
Prepare a model of representing various horizons in the soil profile using a disposed plastic bottle, stones and soil.
Answer:

1. Take soil from your surroundings, clean d: posable plastic bottle and home made paper funnel.
2. Pour the soil into the funnel putting it on the plastic bottle.
3. Now pour some water into the bottle upto its neck. Close the end of the bottle and shake it well. The heavier particles like gravel and sand settle to the bottom of the bottle, wait for a day to get all the soil particles to settle down in the bottle.
4. After one day, you may observe that heavier particles like gravel settle at the bottom of the bottle. Above that you may find sand particles. Just above the sand particles, you may find very finer particles on the top of the bottle you will find humus floating on the surface of the water.
5. From the top, first you find humus, the plant and animal organic matter which helps the growth of plants.
6. Just below the hurhus, you find clay. Clay traps the water in the soil for the roots to absorb them.
7. Below the clay, sand and gravel, they help to drain the water quickly so that the roots don’t rot.
8. Basing on the percentage of each individual component loam soils may be classified into sandy loam, silty loam and clay loam.
9. Here, the soil taken for this project is sandy loam. Like this way, we can determine the type of soils in our surroundings.

Activities

Activity – 1

Question 1.
How do you observe the plants and small living organisms in a given soil? Write your observations in a table.

Answer:

1. I visited my school garden and the kitchen garden yesterday to observe the plants and small living things in those places.
2. I marked an area of 30 cm × 30 cm. 1 dug the soil to a depth of 4 to 6 cm in the marked area.
3. I carefully sorted out the soil and observed the presence of plants and small living organisms with the help of a hand lens.

I noted down the things 1 found in the given table.

Inference :

1. We can infer that soil consists various plants and dried plant parts etc.
2. It is a good habitat for many small organisms.

Activity – 2

Question 2.
How do you observe the different components of the soil?
Answer:
Aim : To observe the different components of the soil.

Materials required : Soil, beaker, water, polythene bag.

Procedure :

1. Collect a handful of soil sample in a transparent polythene bag and close it tightly.
2. Leave it under the sun for 2 hours we can observe some droplets of water on the inner side of the bag.
3. Fill a beaker with this handful of soil, pour water into it slowly and carefully. Fill the beaker with water and stir well the soil and water.
4. Leave it for undisturbed for some time.

Observations :
Organic substances, dry rotten leaves and roots float on water. Dead and decayed organic matter that mixes with soil is called humus.
My observations and inferences are shown in the table.

Inference :
Soil consists of water, air, organic matter, inorganic matter and organisms.

Activity – 3

Question 3.
How do you identify the type of soil in your science lab?
Answer:

1. We can identify the different types of soils in the line diagram given below.
2. We can determine the soil on the basis of following chart.

Activity – 4

Question 4.
How do you know about soil erosion?
Answer:
Aim : To know about soil erosion.

Procedure :

1. Cut three disposable bottles sidewise and fill with soil as shown in the figure.
2. Put some sprouts of green gram or any other seeds in one bottle and water regularly.
3. Cover the second bottle with dry leaves and leave the third bottle without sowing anything.
4. After a week, the sprouts in the first bottle will grow more.
5. Now, make arrangements to collect the drained water from each bottle by arranging small vessels.
6. Now blow air and pour water slowly in each bottle.

Observation :
In the first bottle containing sprouts, less soil is blown out by air and washed off by water.

Inference :
We can infer that the top soil is washed off by water and blown out by air. Plants help to prevent soil erosion.

Activity – 5

Question 5.
What are the differences in the water table in your locality due to increase in the construction and industries nearby?
Answer:

1. The water levels in the wells are rapidly decreased.
2. Many borewells are not working due to depletion in the water table.
3. People are drilling deeper and deeper borewells to keep up with the dropping water table. It is an expensive task. Hence, they are facing financial troubles.
4. People are facing drinking water shortage in the village.
5. People have to walk for miles to get water for their usage.
6. Many people migrated to different places due to scarcity of drinking water in the village.
7. Population explosion, industrial growth, enhanced agriculture activities, deforestation, decrease in the effective area for seepage and drop in rainfall are other main reasons for the rapid decrease of water table on the earth.

SCERT AP 7th Class Science Study Material Pdf 10th Lesson Changes Around Us Textbook Questions and Answers.

AP State Syllabus 7th Class Science 10th Lesson Questions and Answers Changes Around Us

7th Class Science 10th Lesson Changes Around Us Textbook Questions and Answers

Improve Your Learning

I. Fill in the blanks.

1. Changes in which new substances are formed are called ______ changes.
2. Magnesium + Oxygen → ______
3. Milk converted to curd is ______ change.
4. Rusting of iron is protected by ______ process.
Answer:
1. Chemical
2. Magnesium Oxide
3. Chemical
4. Galvanisation

II. Choose the correct answer.

1. When a woolen yarn is knitted to get a sweater, the change can be described as
a) Physical change
b) Chemical change
c) Endothermic reaction
d) Exothermic reaction
Answer:
a) Physical change

2. The chemical chancre among the following is ______
a) Water to clouds
b) GroWth of a tree
c) Cow dung to bio gas
d) Ice to water
Answer:
b) GroWth of a tree

3. Which is an example of a periodic change?
a) Earth quake
b) Formation of rainbow
c) Occurrence of tides in sea
d) Showering of rain
Answer:
c) Occurrence of tides in sea

4. Photosynthesis by green plant is a
a) Physical change
b) Chemical change
c) Reversible change
d) None of the above
Answer:
b) Chemical change

III. Matching.

Answer:

IV. Answer the following questions.

Question 1.
Distinguish physical and chemical changes.
Answer:

Question 2.
When a candle is burnt, what type of changes takes place? Give another example of the similar process.
Answer:

1. When a candle is burnt both physical and chemical changes take place.
2. Burning of candle giving heat and light and reducing its size is a chemical change.
3. The wax melted during burning again condenses to solid wax is a physical change.
4. Part of the candle burnt is a permanent change and it cannot be reversed.
5. Due to the burning of the candle, carbon dioxide and water vapour are produced.

Examples:

1. Burning of LPG in our kitchen.
2. Liquid state of LPG in the cylinder is converted into gaseous state when comes out This is a physical change.
3. When LPG burns in air heat is produced, this is a chemical change.

Question 3.
Define crystallization.
Answer:
The process of separating a soluble solid from the solution by heating or evaporating is called crystallization.

Question 4.
Guess the consequences of burning crackers during festivals and celebrations.
Answer:

1. Firing crackers during festivals and celebrations increase the concentration of dust and pollutants in the air.
2. The dust particles get settled on the surrounding surfaces which are packed with chemicals like copper, zinc, sodium and magnesium. They cause damage to paintings.
3. The quality of ambient air will be decreased drastically.
4. Firing of crackers causes lot of sound pollution.
5. The oxides of sulphur pollute the air and causes lung diseases to human beings.
6. The increase in levels of air pollutants cause acid rains, corrosion of objects and decrease in visibility.

Question 5.
Prove experimentally chemical change is a permanent change.
Answer:

Aim : To prove chemical change is a permanent change.

Materials required :
Magnesium ribbon, water, match box, bunsen flame.

Procedure:
1) Take a small piece of Magnesium ribbon.

2) Burn it on a flame we will find brilliant white dazzling light leaving a powdery substance behind.

3) This is because when magnesium burns in the presence of oxygen, it forms magnesium oxide in the form of powdered ash. This is a new substance.
Magnesium + Oxygen → Magnesium Oxide (new substance)
This is a permanent change.

4) Now, take a small quantity of Magnesium oxide and mix it with a small quantity of water and dissolve it.
Magnesium Oxide + Water → Magnesium Hydroxide (new substance)
This is also a permanent change.
Here also another new substance is formed.

5) By testing this new substance with blue and red litmus papers. Red litmus turns blue. Then Magnesium Hydroxide is a base.

Inference :
Changes that occur with the formation of new substance with different chemical Coposition or transformation of a substance into another substance with the evolution or absorption of heat; or light energy are termed as chemical changes. These are permanent changes.

Question 6.
Guess the reasons for increase of plastic pollution.
Answer:
Main reasons for increase of plastic pollution :

1. Rising human population and their needs, people depend on plastic.
2. The food industry which packs everything on plastic.
3. Increase in usage of plastic bottles and container caps.
4. Indiscriminate usage of plastic bags and carriers.
5. Over usage of plastic straws and stirrers.
6. Lack of proper management of plastic waste.
7. Unawareness among the public about the hazardous affects of plastic wastes.
8. People are not following the 3’Rs (Recycle – Reduce – Reuse) method to reduce plastic wastes.

Question 7.
How can you appreciate the role of periodic changes in nature?
Answer:

1. Changes that are repeating at regular intervals of time are called as periodic changes.
2. Formation of day and night, for every 12 hours the sun rise and the sun set are repeating.
3. Seasons like summer, rainy, winter and spring occur every year at regular intervals.
4. The full moon and new moon repeats every month.
5. Heart beat of human beings takes place periodically.
6. Low and high tides in sea are periodic.
7. All these changes are periodically taking place in nature.
8. They provide us all comforts to live on this earth. I appreciate these periodic changes in nature for providing a happy life on this earth.
9. Without these changes in environment, life of us would become impossible.

Question 8.
Suggest some methods to prevent rusting of iron articles.
Answer:

1. The problem of rusting of iron and other metal articles is common experience in almost every home.
2. It spoils beautiful articles and makes them look ugly.
3. The following are some of the ways to prevent the rusting of iron.
   a) Do not allow the iron articles to come in direct contact with Oxygen in the air, water or both.
   b) Apply a coat of paint or grease on an iron article.

Question 9.
Ravi prepared carbon-dioxide using baking soda and vinegar. Carbon-dioxide changed lime water into milky white. Represent this experiment in a diagram with labelling.
Answer:

Preparation of carbon dioxide

7th Class Science 10th Lesson Changes Around Us InText Questions and Answers

7th Class Science Textbook Page No. 54

Question 1.
What change do you observe after removing mehandi applied on your palms?
Answer:
The hands get red colour after removing mehandi.

Question 2.
Can we clear the printed letters on paper. Why?
Answer:
No, it is a permanent change.

Question 3.
Water dispenser gives hot, normal and cold water. Is this natural or man made?
Answer:
Man-made.

7th Class Science Textbook Page No. 55

Question 4.
What is change?
Answer:
An act or process through which something becomes different.

Question 5.
How do we know that something has changed?
Answer:
By observing the changes in shape, size, colour and chemical properties.

Question 6.
What are the possible reasons for that change?
Answer:
They may be because of physical or chemical changes.

Question 7.
Is there any involvement of human beings?
Answer:
No, these are natural changes.

7th Class Science Textbook Page No. 56

Question 8.
Is there any change in its shape?
Answer:
Yes, it’s size will increase.

Question 9.
How does it happen?
Answer:
The air blown into the balloon occupies the space and the balloon becomes bigger in size. ,

Question 10.
Is it by itself or by anybody else?
Answer:
It is a man made change.

Question 11.
So what type of change it is?
Answer:
This is a man made change.

Question 12.
How much time they require?
Answer:
They require longer periods. It is a slow process.

7th Class Science Textbook Page No. 57

Question 13.
Have you ever noticed the following changes in our daily life?
Answer:
Yes. It is also a reversible change.

7th Class Science Textbook Page No. 58

Question 14.
Do the formed substance differs from original substance?
Answer:
Yes. The formed new substance is completely different.

Question 15.
Can we get original substance by reversing the conditions?
Answer:
No.

7th Class Science Textbook Page No. 50

Question 16.
Have you seen large crystals of sugar (Missrf) or crystal salt?
Answer:
Yes.

Question 17.
Do you know how we get these crystals?
Answer:
Yes. We get them through crystallization.

Question 18.
Have you ever observed the formation of small sugar crystals on sweets like Jilebi and badushah, which are kept aside for a long period?
Answer:
Yes.

Question 19.
What is the reason for this?
Answer:
It is because of crystallization.

Question 20.
What changes do you notice at the end?
Answer:
We notice the formation of large size crystals of sugar at the bottom of the beaker.

Question 21.
Do you find any crystals in the solution?
Answer:
No, we will find the crystals at the bottom of the beaker.

Question 22.
What type of change it is?
Answer:
It is a physical change.

7th Class Science Textbook Page No. 62

Question 23.
In Which cases new substances are formed?
Answer:
In chemical changes, we get new substance.

Question 24.
Have you observed rusting of iron, curdling of milk?
Answer:
Yes, I observed many times.

Question 25.
Do we get the same substance after change? Is the change is temporary or permanent?
Answer:
No, it is a permanent change.

Question 26.
Does the ash formed look like Magnesium ribbon?
Answer:
No.

Question 27.
Do you think the magnesium ribbon and the ash have the same composition?
Answer:
No

Question 28.
What do you observe?
Answer:
We get Magnesium Hydroxide.

Question 29.
Do you observe any change in the state of the substance?
Answer:
It is in liquid state (from solid state)

Question 30.
Is it an acid or base?
Answer:
Base.

7th Class Science Textbook Page No. 63

Question 31.
Did you observe iron nails, iron gates, iron benches or pieces of iron left in the open ground for a long time?
Answer:
Yes.

Question 32.
Did you observe any change in colour?
Answer:
We can observe a brown colour layer on the surface of iron articles.

Question 33.
How can we protect the iron articles from rusting?
Answer:
Through a process called Galvanization.

7th Class Science Textbook Page No. 64

Question 34.
Are there any other ways by which rusting of iron can be prevented?
Answer:
When the iron articles are coated with metals like chromium or zinc, we can prevent them from rusting.

Question 35.
Have you observed the handles of bicycles, metal rims of bicycle and motor cycles?
Answer:
Yes.

Question 36.
Do these articles rust? If not why?
Answer:
No, because they are coated with zinc or chromium.

Question 37.
What changes do you notice?
Answer:
We can notice a brown layer on their outer surface.

Question 38.
Can you prevent the browning of cut vegetables and fruits?
Answer:
Yes.

Question 39.
Have you observed your mother keeping the cut potatoes or brinjals in cold water?
Answer:
Yes.

7th Class Science Textbook Page No. 65

Question 40.
In which fruit or vegetable do you notice change in colour?
Answer:
In Apple, Brinjal and Potato.

Question 41.
Why does this change occurs?
Answer:
Because some vegetables and fruits react with oxygen in the air when they cut. Due to this oxidation process, brown layer is formed on the surface of these fruits and vegetables.

Think & Respond

Question 1.
When food gets spoiled, it produces a foul smell. Shall we call this change as a chemical change?
Answer:
When food gets spoiled by micro organisms, it produces a foul smell. By the action of the enzymes released by these microbes, the components of the food undergo chemical changes. Due to this, the food emits foul smell. It is a permanent change and irreversible in nature.

Question 2.
You know that plants produce their food by a process called photosynthesis. Can we call photosynthesis a chemical change?
Answer:
Photosynthesis is a chemical change. Here, carbondioxide is reduced to glucose. In this process oxygen is evolved. It is a permanent and irreversible change. New substance are formed.

Question 3.
Do all the materials react with oxygen in the air?
Answer:
No.

Question 4.
Observe Gold and Silver. You wear them in the form of ornaments. Even if they get exposed to air for long time, they do not change their colour. Why?
Answer:
Metals like gold and silver, even if they are exposed to air for a long time, they do not change colour or get rusted.

It means that they are resistant to corrosion which is the reason why we use them in making ornaments.

Activities and Projects

Question 1.
Collect information on the process of artificial ripening of fruits in fruit market and discuss whether it is useful or harmful.
Answer:

1. Calcium carbide more commonly known as “masala” is used for artificial ripening of fruits. It is very harmful to health.
2. Calcium carbide is a carcinogenic agent.
3. The most important precaution to avoid eating such artificially ripened fruits is to go in for fruits and vegetables which are not unseasonal.
4. Always wash the vegetables and fruits properly before consuming.

Question 2.
When you burn a piece of wood different changes take place analyse the following. Predict possible changes and list them all.
a) Are there any physical changes among them?
b) How many forms of energy are released in the change?
c) What chemical changes do you notice?
d) Explain briefly why these occur.
Answer:
a) No physical changes is observed.
b) The energy is released in the form of heat sound and light energy.
c) When a piece of wood is burnt a new material is formed (ash). We also notice change in shape and size of new materials (powder). This type of change which leads to form new substance is called chemical changes.
d) Wood turns into carbondioxide and ash
Carbon (Wood) + Oxygen (Air) → CO₂ + Ash

Activities

Activity – 1

Question 1.
What changes do you observe, When a balloon is blown?
Answer:
Change in the shape of balloon is done by blowing air into it. This is a man made change. When we left off the air from it, it returns to its normal shape. This is a physical change and reversible one.

Activity – 2

Question 2.
Observe the changes mentioned in the following table and complete it.

Answer:

Activity – 3

Question 3.
What changes do you notice when few pieces of ice in a beaker are heated? What do you mean by a physical change? Before heating After heating After freezing
Answer:

1. Take few pieces of ice in a beaker and heat them on burner as shown in the figure.
2. We notice that ice slowly melts and becomes water and on further heating it changes to steam.
3. If we reduce the temperature, the water vapour changes back to water and when temperature is further reduced it changes to ice.
4. In the above activity we notice the change of the state of ice to water and to vapour but the substance, water, remains the same.
5. Changes of this type where no new substance is formed are known as physical changes.
6. When a material undergoes a change in shape, size, colour or state it is called a Physical Change.
7. Generally, no new substance is formed in a physical change.

Activity – 4

Question 4.
Describe how do you perform the activity to observe the reaction of vinegar with baking soda?
Answer:

1. First set up the apparatus as shown in Fig.
2. Take a teaspoon of vinegar (acetic acid) in a test tube and add a pinch of baking soda (Sodium bicarbonate) to it.
3. You observe bubbles coming out with a hissing sound. Pass this gas through freshly prepared Limewater (Calcium Hydroxide).
4. Limewater changes to milky white showing that the gas sent into the test tube is Carbon dioxide.
5. Vinegar + Baking Soda → Sodium acetate + Carbon dioxide + Water
6. Carbon dioxide + Lime Water → Calcium Carbonate + Water
7. In these reactions the new substances like Carbon dioxide and Calcium Carbonate are formed. Hence it is a chemical change.
8. When a material undergoes a change in its composition it is called a chemical change.

Activity – 5

Question 5.
Write the approximate time after which they repeat.

Answer:

Activity – 6

Question 6.
How do you produce large size of sugar crystals ? What type of change is it?
Answer:

1. Take a big size test tube. Fill half of it with water. Add some sugar to it and stir it.
2. Keep adding sugar and stirring until saturation is attained.
3. Then heat this sugar solution and add some more sugar to it while stirring continuously.
4. Continue adding sugar till no more sugar can be dissolved in it.
5. Now filter the solution and allow it cool for half an hour.
6. We notice formation of large size crystals of sugar at the bottom of the beaker. Thus the small granules of sugar added changed into large size sugar crystals.
7. This is a physical change.

Activity – 7

Question 7.
Some changes are given in the table. Write possible changes you notice for each case and put (✓) in the appropriate column.
Answer:

1) In the above activity we notice that only in some examples like burning of paper, burning of crackers, change of milk to curd, boiling of egg, etc., a new substance is formed.

2) But in other examples of changes we notice an change in state or colour or size or shape etc but the substance remains same and no new substance is formed.

Activity – 9

Question 9.
Complete the following table.

Answer:

Some fruits and vegetables when cut, react with oxygen in the air. The process of reaction with oxygen is called oxidation. Due to this process brown layer is formed on the surface of fruits and vegetables.

SCERT AP 7th Class Science Study Material Pdf 8th Lesson Wonders of Light Textbook Questions and Answers.

AP State Syllabus 7th Class Science 8th Lesson Questions and Answers Wonders of Light

7th Class Science 8th Lesson Wonders of Light Textbook Questions and Answers

Improve Your Learning

I. Fill in the blanks.

1. Image formed by convex mirror is erect, small and _______
2. Infinite number of images are formed between two mirrors if they are kept at an angle of _______
3. Dentists use _______ mirror to see inner parts of teeth.
4. Image that cannot be obtained on screen is______
Answer:
1. virtual
2. 0°
3. concave
4. virtual

II. Choose the correct answer.

1. In periscope, the angle between two plane mirrors is
a) 0°
b) 30°
c) 45°
d) 60°
Answer:
a) 0°

2. If two plane mirrors are kept at an angle of 180° between them. Then the number of
a) 1
b) 2
c) 3
d) 4
Answer:
a) 1

3. Which of the following is not the property of image formed by a plane mirror?
a) Same size
b) Real
c) Lateral inversion
d) Erect
Answer:
b) Real

4. If a light ray falls on plane mirror along the direction of normal, then the angle of reflection will be
a) 90°
b) 45°
c) 0°
d) 180°
Answer:
a) 90°

5. Which form clear image among the following?
a) Paper
b) Cloth
c) Card board
d) Plane mirror
Answer:
d) Plane mirror

III. Match the following.

Answer:

IV. Answer the following questions.

Question 1.
What is reflection of light? Explain with an example.
Answer:

1. The process of bouncing back of light rays into the same medium after falling on a smooth or rough surface from the light source is called “reflection of light”.
   Example:
2. Take a plane mirror and stand in front of a building in open space during the day. Let the sunlight falls on the mirror. Now rotate the mirror in such a way that a spot of light falls on the wall of building.
3. In the above activity, light rays fall on the mirror bounced back. This process of bouncing back of light rays in the same medium after hitting the surface of an object is called reflection.

Question 2.
Write the laws of reflection of light.
Answer:
There are two laws of reflection :

1. First law of reflection : Angle of incidence is equal to angle of reflection.
2. Second law of reflection : The incident ray, reflected ray and normal to the surface are present in the same plane. Incident and reflected rays are on either side of normal.

Question 3.
Why should we keep the mirror strips in the Periscope parallel to each other? What happens if they are not parallel?
Answer:

1. We should keep the mirror strips in the Periscope parallel to each other. The image of an object formed on the first mirror reflects exactly on the second mirror and then we can see the image. It is possible when the mirror strips in the Periscope parallel to each other.
2. If they are not parallel, the image of an object formed on the first mirror does not reflects on the second mirror and we cannot see the image through the second mirror.

Question 4.
What precautions do you take while getting the image of burning candle using a mirror?
Answer:

1. Keep the candle as its flame is in the line of the mirror.
2. Keep the mirror as its plane opposite to the screen.
3. Do the experiment in a dark room.
4. Take care while handling the candle with flame.

Question 5.
Write the properties of images formed by concave mirror.
Answer:
The properties of images formed by concave mirror.

1. It can form both real and virtual images.
2. It produces erect and inverted images
3. It also produces small same size and bigger images depending on the position of object in front of it.

Question 6.
Draw the diagram show regular reflection and diffused reflection of light.
Answer:

Question 7.
Where do you find multiple images formed by plane mirrors in your day-to-day life?
Answer:

1. In sweet shops mirrors are arranged in such a way that multiple images of sweets can appear.
2. In saloon and beauty parlours mirrors are arranged in such a way that the customers can view his images in all directions.
3. In bathrooms and dressing rooms also, we can observe multiple images.
4. In Kaleidoscope we can observe multiple images.

Question 8.
Where do you find irregular reflections in your daily life?
Answer:
We can find irregular reflections on unpolished marbles floors, scratched steel vessels, broken mobile screens, disturbed water surfaces, and on the rough surfaces of plastic sheets, metal sheets, etc.

Question 9.
Write the applications of spherical mirrors in daily life.
Answer:
Applications of concave mirrors:

1. Concave mirrors are used by ENT doctors as Head Mirrors.
2. Dentists also use concave mirrors to get a bigger image of the teeth.
3. Eye specialist using a special instrument called Ophthalmoscope. It is fitted with a concave mirror having a small hole near its center.
4. Concave mirrors are used to reflectors in a torch light or the headlights of vehicles.
5. These are used in microscopes.

Applications of convex mirrors:

1. Convex mirrors are used as Rear-view mirrors in vehicles.
2. Convex mirrors are also used at the junctions of roads.
3. Convex mirrors are used at ATM machines.
4. Convex mirrors are used for security purpose at factories, offices, etc.

7th Class Science 8th Lesson Wonders of Light InText Questions and Answers

7th Class Science Textbook Page No. 16

Question 1.
What do you observe in the picture? Mention the different objects in the scenery.

Answer:
Trees, river, hills, rainbow, steps, boat, a boy, a girl, butterfly, water, plants, wooden bridge.

Question 2.
Can we see all these objects during night time?
Answer:
No, we cannot see all these objects during night time.

7th Class Science Textbook Page No. 17

Question 3.
Where does the light come from?
Answer:
Light comes from different objects called sources of light.
Ex : Sun, candle, tubelight.

Question 4.
Name some sources of light around you.
Answer:
Sun, candle, tubelight, bulb, torch light, match box etc .

Question 5.
Do these sources release light on their own?
Answer:
Sources like sun, stars emit light on their own.
Sources like bulb, torch light, candle do not emit light on their own.

Question 6.
Can you give some other examples for natural sources of light?
Answer:
The moon, stars and the sun.

Question 7.
Do you know how this light travel from the source?
Answer:
Actually, light is not a single ray, but a bundle of rays- This bundle of light rays are called beam of light rays. .

Question 8.
What do we call the path of light?
Answer:
The direction or path along which light travels is called a ray of light.

7th Class Science Textbook Page No. 18

Question 9.
How are we able to see the objects?
Answer:
The light fall on the objects and reflects and reach to our eye.

Question 10.
Is only light enough to see the objects around us?
Answer:
Yes, light is enough, but reflected light should reach our eye.

7th Class Science Textbook Page No. 19

Question 11.
In the activity-2, is there any reflection from the reflected light?
Answer:
Yes, there is reflection from the reflected light.

7th Class Science Textbook Page No. 23

Question 12.
We are able to see our image in the mirror. Can we catch our image bn screen?
Answer:
No. We cannot catch our image on screep.

7th Class Science Textbook Page No. 24

Question 13.
Are the images formed by plane mirrors real or virtual?
Answer:
Plane mirror forms virtual image.

Question 14.
Have you observed the arrangement of plane mirrors in a sweet shop? How many images did you find?
Answer:
Yes, I have observed the arrangement of plane mirrors in a sweet shop. So many images are formed.

7th Class Science Textbook Page No. 25

Question 15.
How many images are formed when the angle between two mirrors is zero?
Answer:
Number of images (n) = (360°/θ) – 1= ∞ , from the formula, we can find infinite number of images are formed. –

7th Class Science Textbook Page No. 26

Question 16.
Have you ever seen your image in rearview mirror of your father’s, motor cycle?
Answer:
Yes.

Question 17.
Is it same as the image seen in the mirror of your dressing table?
Answer:
No

Question 18.
What difference did you observe?
Answer:
Image is small in and closure.

Question 19.
What may be the reason for the difference?
Answer:
May be shape of the surface of the mirror.

Question 20.
Touch the surface of the rearview mirror. Is it same as plane mirror?
Answer:
No. It is not same as plane mirror. It is in curved in shape.

7th Class Science Textbook Page No. 28

Question 21.
Do you know the use of spherical mirrors in your daily life?
Answer:
Concave mirrors are used by dentists, ophthalmologists, ENT doctors and also in head lights of vehicles. Convex mirrors are used as rear view mirrors in vehicles and safety mirrors at curved roads.

7th Class Science Textbook Page No. 29

Question 22.
Have you ever observed the surface of reflection in a torch light or the headlights of vehicles?
Answer:
Yes, they are spherical in shape.

7th Class Science Textbook Page No. 30

Question 23.
Can you recognize the mirrors used beside the drivers in vehicles?
Answer:
These are convex mirrors.

Question 24.
Can you now recognize the characteristics of image from rear view mirror?
Answer:
Erect, virtual and smaller images are formed.

Question 25.
Do all the objects reflect the light rays falling on it?
Answer:
No.

Question 26.
Do you know why did paper burnt with a magnifying glass?
Answer:
The paper burned as the magnifying glass concentrated the sun’s rays at one place on the paper.

Question 27.
Doesthe magnifying glass reflect the light falling on it?
Answer:
No.

Think & Respond

7th Class Science Textbook Page No. 23

Question 1.
Deepak saw a vehicle on the road. He was surprised to see that the word on it. What was that word? Why was it written in a strange manner?
Answer:

1. The word is AMBULANCE.
2. AMBULANCES are emergency vehicles.
   It is important to give way to ambulances.

The drivers can see the rear coming vehicles through the rear view mirror of the vehicles. Objects and letters appear in reverse means in left right inversion in mirrors. So letters in the wf>rd AMBULANCE also appear in reverse and cannot understand the word to the drivers.

If the word is written in reverse (as in mirror image) on the ambulance, it appears normally and readably. Drivers can read the word AMBULANCE and give a way to ambulance immediately.

Activities and Projects

Question 1.
Large sized concave mirrors are used to focus sun rays in solar cookers and solar heaters.Make a solar cooker of your own by using this principle and exhibit in your school science fair.
Answer:

Making of solar cooker :

1. A concave mirror focuses parallel sun rays at the focal point of the mirror.
2. So with a small concave mirror .we can heat up and burn paper.
3. In the same way make a big concave mirror to heat up a vessel.
4. Make a wooden/ iron frame in the shape of TV dish.
5. Cut acrylic mirror sheets into 8 or 12 pieces in the shape of isosceles triangles with a height equal to the radius of dish antenna.
6. The bases of 8 or 12 triangles together make the circumference of the dish.
7. Stick the triangle mirrors to the dish.
8. Our solar heater/cooker is ready.
9. Arrange it so that concave part faces sun.
10. Find its focal point and place a vessel at that point.
11. It will get heated. We can even cook rice in that vessel.

Question 2.
Prepare a report by collecting data on the uses of spherical mirrors.
Answer:
Spherical mirrors are two types : They are 1) concave mirror 2) convex mirror.

1) Concave mirror :
Concave mirrors have a smooth curved surface inwards. Light rays are converged at one point by a Concave mirror. Real and virtual images can form the concave mirror.

The applications of concave mirror in our daily life :
Dentists :
Concave mirrors are used by dentists in the examination of teeth.

ENT doctors:
These are used by ENT doctors to examine the body parts.

Shaving mirrors :
During shaving, the concave mirror forms an enlarged and erect image of the face when the mirror is held closer to the face.

Optical instruments:
Ophthalmoscope concave mirrors are used in optical instruments such as Ophthalmoscope.

Astronomical telescopes:
These are used in telescopes and other devices. Headlights : Concave mirrors are widely used in headlights of automobiles and motor vehicles, torchlights, railway engines, etc. as reflectors. The light source is placed at the focus of the mirror, so after reflecting the light rays travel over a huge distance as parallel light beams of high intensity.

Solar cookers :
Concave mirrors are also used in solar cookers. Concave mirrors are also used in satellite dishes, electronic microscope, visual bomb detectors, etc.

2) Convex mirror .
Convex mirrors have a smooth curved surface outwards. Light rays are diverged at one point by a Convex mirror. Only virtual images can form the convex mirror.

The applications of convex mirror in our daily life.

Rear-view mirrors:
These are convex mirrors. These mirrors form images of objects spread over a large area. So, these help the driver to see the traffic behind them. Hence these are used as Rear-view mirrors.

Road safety:
Convey mirrors kept at the corners of curved roads to avoid accidents. Convex mirrors form images of vehicles on both sides of curved road. These mirrors are also used at the mnctions of roads.

Question 3.
Make a list of objects in your school and home, that works like a mirror. Make a report why they work like that.
Answer:

1. Plane mirror : It has plane surface. So it reflects the light.
2. Water surface : It has plane surface, when it was stable. So it reflects the light.
3. Tiles of floor : It has plane surface. So it reflects the light.
4. Almara : It was painted and has a smooth plane. So it reflects the light.
5. Steel plate : It has a smooth plane. So it reflects the light.
6. Concave and convex mirrors : It has plane surface. So it reflects the light.
7. Computer screen : It has plane surface. So it reflects the light.
8. Steel spoon : It has plane surface. So it reflects the light.

Question 4.
Take an empty tooth paste box and two mirror strips of required size and make a periscope.
Answer:
Collect the following materials to make your own periscope.

1. Empty tooth paste box, two mirror strips, scale, pencil, blade, gum.
2. Take an empty tooth paste box.
3. Close the ends and draw two squares at both the ends by using scale and pencil.
4. Draw diagonals to the square boxes, such that the two diagonals facing each other.
5. Make two slits with the help of blade along the diagonals.
6. Make sure that the size of mirror should be equal to the length of slits.
7. Fix the mirror strips in the slits in such a way that reflecting surfaces of mirror strips face pach other.
8. Fix the mirror strips firmly to the box by using gum.
9. Cut out two windows on the narrow sides such that the windows should open directly on the reflecting surfaces of the mirror strips. Now the Periscope is ready.

Activities

Activity – 1

Question 1.
Write an activity to show the following type of light rays,
i) Parallel beam of light rays
ii) Converging beam of light rays
iii) Diverging beam of light rays
Answer:
i) Parallel beam of light rays:
Light rays which travel parallel to each other are called Parallel beam of light rays. To understand about parallel beam of light rays observe situation 1.

Situation-1 :

1. Take a plank and cardboard.
2. Make small slits on cardboard.
3. Keep the cardboard on the plank perpendicular to it.
4. Keep it in sunlight during afternoon as shown in figure.
5. The light rays from the sun fall on the cardboard and passed through the slits.
6. We can observe that the light rays are travelling parallel to each other. These are called parallel beam of light rays.

ii) Converging beam of light rays :
“Light rays which travel from different directions to meet at a point are called as Converging beam of light rays”.
To know clearly about converging beam let us observe situation 2.

Situation-2 :

1. Recall the above situation.
2. Arrange an acrylic mirror in the path of light rays as shown in the figure.
3. The light rays meet at a point after bouncing back from the mirror. These are called converging beam of light rays.

iii) Diverging beam of light rays :
“Light rays which travel from a source moving in different directions are called as Diverging beam of light rays.” To understand about diverging beam, let us observe situation 3.

Situation-3 :

1. In the above situation, arrange the acrylic mirror in the path of light rays as shown in the figure.
2. After bouncing back from the mirror light rays travel in different directions

Activity – 2

Question 2.
Write an activity to Understand the reflection of light.
Answer:
“The process of bouncing back of light rays into the same medium after falling on a smooth or rough surface from the light source is called “reflection of light”. Let us understand this phenomenon with the following activity.

1. Take a torch and enter into a dark room.
2. Observe the objects in darkness. We cannot see any object.
3. Switch on the torch and focus it on the objects. We can see the objects.
4. Keep a card board between your eyes and object.
5. Now try to see the objects. We cannot see any object. ,
6. From the above activity we can conclude that objects are visible only when light falls on the objects and bounces back to the eye.

Activity – 3

Question 3.
Write an activity to understand the reflection of light.
Answer:

1. Take a plane mirror and stand infront of a building in open space during the day.
2. Let the sunlight falls on the mirror.
3. Now, rotate the mirror in such away that a spot of light falls on the wall of building.
4. Light rays from the sun fall on the mirror and bounced back. The spot of Light on the wall is the image of sun.
5. In this activity, light rays fall on the mirror and bounced back.
6. This process of bouncing back of light rays in the same medium after hitting the surface of an object is called reflection.

Activity – 4

Question 4.
Write an activity to understand the regular reflection and irregular reflection of light.
Answer:
Reflection from a smooth and shiny surface is called regular reflection.

Reflection from an irregular or uneven surface is called irregular reflection or diffused reflection.

Let us understand these from the activity below.

1) Focus the light from a source on the objects mentioned in the given table and try to get the image of the objects.

2) Record your observations in the table given.

3) From the above table it is clear that light reflects regularly from a smooth and shiny surface and irregularly from an uneven surface.

4) Reflection from a smooth and shiny surface is called regular reflection.

5) Clear images are formed in case of regular reflection.

6) Reflection from an irregular or uneven surface is called irregular reflection or diffused reflection. Images are not clear or sometimes cannot form the images at all in case of irregular reflection.

Activity – 5

Question 5.
How can you verify the laws of reflection?
Answer:

1. Take a White paper and spread it on a drawing board or cardboard.
2. Draw a straight-line AB at the center of paper by a pencil.
3. Mark a point O at the center of AB.
   
4. At the point ‘O’ draw a perpendicular line ON to AB.
5. ON is called normal to the surface.
6. ake a protractor and place it on white paper in such a way that the zero edge of the protractor coincides with the point O on AB as shown in figure.
7. Mark different angles starting from 10° to 80° on both sides of ON.
8. Now place a plane mirror on the line AB with the help of two clips such that the surface of the plane mirror is perpendicular to the surface of the white paper.
9. Take a laser pointer and focus it on plane mirror at ‘O’ making an angle of 40° with the line ON.
10. Observe the reflected ray from the mirror.
    

    Angle of incidence	Angle of reflection
    1. 20°	20°
    2. 40°	40°
    3. 60°	80°
    4. 80°	80°

11. The angle made by incident ray with the normal ON is called angle of incidence i.
12. The angle made by the reflected ray with the normal is called the angle of reflection r.
13. Focus laser pointer at different angles of incidence.
14. Observe the angles of reflection in each case and tabulate the values.

From the above observations you can conclude that the angle of incidence is always equal to angle of reflection.
(OR)

This is the first law of reflection.
1) From the above activity you can also observe that Incident ray, reflected ray and normal are present in the same plane and incident, reflected rays are on either side of normal.

2) The incident ray, reflected ray and normal to the surface are present in the same plane and incident, reflected rays are on either side of normal.
This is the second law of reflection.

Activity – 6

Question 6.
How can you verify the following characteristics of image by plane mirror?
1) Object distance is equal to image distance.
2) Size of the object is equal to size of the image.
Answer:
Let us verify the above characteristics by the following activity.
1) Take a chess board.
2) Fix a plane mirror vertically at the one end of the chess board as shown in the figure. Place a sharpener on one of the square boxes on the chess board.
3) You can see the image of sharpener in the mirror.

4) Count the number of square boxes between the mirror and the sharpener. At the same time count the number of square boxes between the mirror and the image of sharpener. The number of square boxes equal in both the cases.
Conclusion 1:

5) From the above activity you can conclude that the distance of the object from the mirror is equal to the distance of image from the mirror.

6) The distance of the object from the mirror is called object distance. The distance of the image from the mirror is called image distance.

7) In the above activity observe the size of object [sharpener] and image.

8) You will find that the size of image and object are equal.

Conclusion 2:
From the above activity you can conclude that the size of the object is equal to size of the image.

Activity – 7

Question 7.
How can you verify the following characteristic of image by plane mirror?
Laterally inverted image is formed, (left and right alternates)
Answer:

1. Stand in infront of a plane mirror and raise your right hand.
2. Observe the image formed in the mirror.
3. Now lower the right hand and raise the left hand.
4. Observe the changes you noticed in the image.
5. Your right hand appears left and left hand appears right in the image.
6. Such a shift of lateral side of images in opposite direction is called lateral inversion.

Conclusion:
So images formed by plane mirrors undergo lateral inversion

Activity – 8

Question 8.
How can you verify the following characteristics of image by plane mirror?
* The image formed is always virtual and erect.
Answer:

1. Place a burning candle infront of the plane mirror.
2. Observe the image of burning candle in the mirror.
3. Now place a white paper behind the candle.
4. Try to get the image of candle on paper.
5. If your answer is ‘YES’, such type of image which we get on screen is called real image.
6. If your answer is ‘NO’, such type of image which cannot get it on screen is called virtual image. •
7. Plane mirror forms only virtual image.
8. In the above activity, the image of burning candle is erected.
9. We can see the erect image of the object in the mirror.

Conclusion:
Thus, we can conclude that plane mirrors form virtual and erect image.

Activity – 9

Question 9.
Write an activity to understand the relation between the arrangement of mirror and number of images.
(OR)
Derive a formula for number of images formed between two mirrors.
Answer:

1. Take a drawing board, spread a white sheet on it.
2. Draw a semicircle on the white sheet.
3. Mark the angles from 0° to 180° with the help of protractor.
4. Take two plane mirrors of same size join them with cellophane tape as shown in the figure.
5. Keep the mirrors on the semicircle such that the angle between the mirrors is 120° .
6. Now bring a burning candle in between the mirrors.
7. Observe the number of images formed by the two Mirrors.
8. Change the angles between the mirrors from 120° to 90°, 60°, 45°, and 30° respectively.
9. Observe the number of images formed in each position. Tabulate your observation.

In this way we. can derive the formula to find out the number of images formed between two mirrors.

Number of images (n) = (360°/θ) -1 where 0 is the angle between the mirrors

Activity – 10

Question 10.

How do you make a Royal Road in a Shoe Box by using plane mirror?
(OR)
How do you prepare a Fancy item by using the phenomena of multiple reflections of plane mirrors?
Answer:

1. Fix two plane mirrors on the opposite sides of a shoe box with their reflecting surfaces facing each other.
2. Draw a road on the bottom of shoe box between the mirrors.
3. Arrange two LED street lights on both sides of road.
4. Make a small hole on mirror side of shoe box and scrape off a little of colour coating from the mirror on that place.
   Observe the scenery inside the box through this hole.
5. Light rays from the LED fall on the first mirror and then continuously undergone multiple reflections.
6. That’s why we see a long road With full of LED lights.

Activity – 11

Question 11.
How do you make a periscope by using plane mirrors?
(OR)
Make your own periscope.
Answer:
Required materials:
Empty Incense stick box [Agarbatt(box], two mirror strips, scale, pencil, blade, gum.

Procedure:

1. Take an empty Incense stick box.
2. Close the ends and draw two squares at both the ends by using scale and pencil.
3. Draw diagonals to the square boxes, such that the two di-agonals facing each other.
4. Make two slits with the help of blade along the diagonals.
5. Make sure that the size of mirror should be equal to the length of slits.
6. Fix the mirror strips in the slits in such a way that reflecting surfaces of mirror strips face each other.
7. Fix the mirror strips firmly to the box by using gum.
8. Cut out two windows on the narrow sides such that the windows should open directly on the reflecting surfaces of the mirror strips as shown in figure.
9. Now your Periscope is ready.
10. You can use this to see the objects outside the room through the window while hiding yourself in the room

Activity – 12

Question 12.
Write an activity to understand different shapes of spherical mirrors.
Answer:

1) Take a stainless-steel serving spoon.
2) Look into it by bringing the outer bulged side of the spoon near your face.
3) Do you see your image in it? (Yes)
4) Did you observe any difference in image from what you see in plane mirror? (Yes)

10) Try to increase the distance of the spoon from your face.
11) Here the surface of the spoon act as a mirror but the surface is not plain.
12) The outer surface of the spoon is curved out like the outer surface of a sphere.
13) The inner surface of the spoon is like the part of inner surface of a sphere.
14) These mirrors are the parts of spheres. So these kinds of mirrors are called spherical mirrors.

Spherical mirrors are of two types :

1. Convex mirrors (Reflecting surface bent outward)
2. Concave mirrors (Reflecting surface bent inward)

Activity – 13

Question 13.
Characteristics of image formed by a concave mirror.
Take a ‘V’ shaped wooden stand. Keep a concave mirror on it. Place a lighted candle at a distance of about 50 cm in front of the mirror. Try to get clear image of the candle flame on a white screen or white paper by moving the screen towards and away from the mirror. Make sure that the screen is not placed in between burning candle and mirror.

Place the lighted candle at different distances in front of the mirror by moving it towards the mirror. Try to get a clear image on the screen at each position. Note your observation in the table given below.
Answer:

From the above table, you can conclude that a concave mirror can form real and virtual images, erect and inverted images, smaller, same size, and bigger images depending on the position of the object in front of it.

SCERT AP 7th Class Science Study Material Pdf 6th Lesson Electricity Textbook Questions and Answers.

AP State Syllabus 7th Class Science 6th Lesson Questions and Answers Electricity

7th Class Science 6th Lesson Electricity Textbook Questions and Answers

Improve Your Learning

I. Fill in the blanks.

1. Longer line in the symbol for a cell represents its ____ terminal and the shorter line represents ____ terminal.
2. Iron box works based on ____ effect of electric current.
3. The symbol for open switch is _______ .
4. The combination of two or more cells is called a ____
5. Expand MCB ____
Answer:
1. Positive, Negative
2. heat
3.
4. battery
5. Miniature Circuit Breaker

II. Choose the correct answer.

1. When cells are connected in series, it has
a) Single loop connection
b) Two loops
c) Many loops
d) None
Answer:
a) Single loop connection

2. Four bulbs are connected in parallel. When one bulb is removed then the remaining bulbs are
a) Put off
b) Continuously glowing
c) Blinking
d) None
Answer:
b) Continuously glowing

3. Statement 1: Generation of heat due to electric current is known Magnetic effect of electricity.
Statement 2 : An electromagnet works on magnetic effect of Electricity.
a) Both statements are true.
b) Both statements are false.
c) Statement 1 is true, Statement 2 is false.
d) Statement 1 is false, Statement 2 is true.
Answer:
d) Statement 1 is false, Statement 2 is true.

4. Ramu’s house has five 60W bulbs. If they used all the bulbs for 5 hours. Then the power consumed by him

a) 1500 KWH
b) 0.3 KWH
c) 70 KWH
d) 1.5 KWH
Answer:
d) 1.5 KWH

5. Which of the following works on the basis of heating effect of electric current?
a) Electric Crane
b) Electric Lift
c) Escalator
d) Hair drier
Answer:
d) Hair drier

III.Matching

Answer:

IV. Answer the following questions.

Question 1.
Why are bulbs in series put off when a bulb is removed from it?
Answer:

1. In series connection electricity has only one path.
2. If a bulb is removed from the series connection of bulbs, the circuit becomes open.
3. So, remaining bulbs are put off as the circuit open.

Question 2.
Read the following riddles and answer them.
1. I am used to close-or open the circuit. Who am I?
2. I will give you light. Who am I?
3. I convert chemical energy into electrical energy. Who am I?
4. Without me you cannot connect the electrical components. Who am I?
Answer:

1. Switch
2. Bulb
3. Cell
4. Connecting wires

Question 3.
Give examples for electric appliances which work on the property of heat effect of electricity.
Answer:
Examples for electric appliances which work on the property of heat effect of electricity:

1. Electric heater
2. Electric iron box
3. Soldering gun
4. Electric kettle
5. Electric rice cooker

Question 4.
A cell, 5 bulbs and a switch are connected in a circuit but bulbs are not glowing. Write the possible reasons for this.
Answer:
Possible reasons:

1. May be connected a dysfunctional or less voltage cell.
2. May be switch in off position.
3. Wires may be cut any where or not properly connected.
4. At least one of the bulbs may be damaged (If they are connected in series).
5. All the bulbs may be damaged. (If they are connected in parallel)

Question 5.
Describe the process to prepare an electromagnet.
Answer:
1) Take an iron nail.
2) Wound the insulated copper wire tightly around the nail.
3) Connect the two ends of the coiled copper wire to a battery and a switch in series connection.
4)
5) Place some pins near the iron nail.
6) Now switch on the circuit.
7) Observe that all pins cling to the end of the iron nail.
8) This indicates coiled copper wire around nail acts as magnet when electricity passes through it.
9) It means the coiled copper wire around the nail acts as an electromagnet.
10) Now switch off the circuit.
11) Observe that all pins fall from the iron nail.
12) Hence, we can say that the coiled copper wire does not act as a magnet when no electricity passes through the circuit.

Question 6.
Draw the symbols for the following.
A) Bulb
B) Cell
C) Battery
D) Open Switch
Answer:

Question 7.
Draw a circuit diagram of electrical components in a sequence by using cell, bulb, switch is off mode and connecting wires.
Answer:

Question 8.
How do you appreciate the role of magnetic effect and heating effect in our daily life?
Answer:

1. The production of heat due to the flow of electricity through a wire is called heating effect of electricity.
2. We are using many home appliances like electric iron boxes, electric cookers, electric heaters, geysers, hair dryers which work on the principle of heating effects of electricity.
3. The above said home appliances contain heating elements which produce heat.
4. The production of magnetic force due to the flow of electricity through a wire is called magnetic effect of electricity.
5. Loud speakers, MRI machines, generators, metal detectors, mobile phones, mixer grinders, electric fans, electric bells, electric motors etc.; work based on the magnetic effect of electricity.
6. In this, way, heating and magnetic, effects of electricity are used in medical, automobile, industrial, agricultural etc., fields and also in homes.
7. The devices and home appliances have made our lives more comfortable.
8. Hence, I appreciate the role of magnetic effect and heating effect^ in our daily life.

Question 9.
Prepare some slogans to create awareness on wastage of electricity.
Answer:

1. Save electricity – Save money.
2. Turn off the lights, before leaving.
3. Today’s wastage is tomorrow’s shortage.
4. The less you burn, the more you earn.
5. Save power – Save nation.
6. Be polite – turn off the light.
7. When the sun is bright – say no to tube light.
8. Energy is precious – use 5 star appliances.
9. Leave filament bulbs – Use LED’S
10. Less consumption of power – Leads more comforts in future.

Question 10.
Suggest first aid when a person suffers electric shock.
Answer:
First aid for electric shock :

1. If the shock is severe and the person is unconscious, give mouth to mouth artificial respiration.
2. Sometimes heart beat ceases, at that time keep your palms on his chest and press down and release until the heart beat is recovered. This is called Cardio Pulmonary Resuscitation (CPR).
3. Immediately take him to the hospital.

7th Class Science 6th Lesson Electricity InText Questions and Answers

7th Class Science Textbook Page No. 83

Observe the picture carefully.

Question 1.
What are the electric devices you find in the above picture?
Answer:
1) Bulb 2) Fan 3) TV.

Question 2.
List out the electric devices used in your homes.
Answer:
1) TV 2) Fans 3) CFL bulbs 4) LED bulbs 5) Tube light (LED) 6) Music system 7) Chargers 8) Refrigerator 9) Electric geyser 10) Vapourizer 11) Iron box 12) Calling bell 13) Mixie 14) Wet grinder 15) AC 16) Motor pump 17) Mosquito repellent.

7th Class Science Textbook Page No. 84

Question 3.
Why does a bulb glow when we switch it ON?
Answer:
When we switched ON the bulb electricity flows through the wire and makes the bulb to glow.

Question 4.
What do you observe inside the cell?
Answer:

1. Carbon rod with a metal cap.
2. Carbon powder.
3. Ammonium chloride paste.

Question 5.
Can we make a cell of our own?
Answer:
Yes, we can make a cell by using a zinc plate, copper plate, a small bulb, connecting wires, lemon or orange, crocodile clips.

7th Class Science Textbook Page No. 85

Question 6.
Do you know the type of cell is used in wrist watch?
Answer:
Button cells are used is wrist watches.

Question 7.
How many types of electric cells shown above are known to you?
Answer:
I know the dry cells, lithium cells, button cells and alkaline cells.

Question 8.
Where do we used dry cells?
Answer:
In our daily life we use dry cells in torch lights, wall clocks, radios etc.

7th Class Science Textbook Page No. 86

Question 9.
Does a bulb glow when switch is in off position? Why?
Answer:
When the switch is in off position, bulb does not glow. Because the circuit is opened.

7th Class Science Textbook Page No. 87

Question 10.
Among all these bulbs which bulb consumes less electricity?
Answer:

1. We can observe star symbols (power saving star rating) are marked on electrical appliances.
2. The number of stars on them indicates the energy efficiency of that device.
3. The electrical appliance with more stars consumes less electricity.
4. LED bulbs are more energy savers than other bulbs.

Question 11.
Is there any protection provided for electric devices in our house?
Answer:
Yes. The fuse is used to protect the electric devices in our house.

Question 12.
If there is a power failure only in your house. What do you check first?
Answer:
We will check the fuse first.

Question 13.
Have you seen the electric device shown in the figure. Where is it used?
Answer:

1. The electrical devices shown in the figure are fuses.
2. Fuses are used at meter board to protect the devices from excess flow of electricity.

Question 14.
Is there any other safety device which can be used as a fuse?
Answer:
Yes, MCB can be used as a fuse.

7th Class Science Textbook Page No. 88

Question 15.
Have you ever seen this component?
Answer:
Yes, I saw it. It is a MCB.

Question 16.
Which is a better safety device, electric fuse or MCB?
Answer:
MCB is better, when compared to electric fuse. There is no need to change it often. But wire in electric fuse has to be changed whenever it melts.

Question 17.
Do you know how to show the connections of the electric components in a circuit?
Answer:
Yes. We can show the connections of the electric components in a circuit by its symbols.

Question 18.
What electric components do you find in the figure?
Answer:

1) Switch 2) Bulb 3) Wire 4) Battery.

Question 19.
Is it possible to draw realistic electric components every time? Why?
Answer:

1. Drawing circuit diagrams with realistic components is difficult.
2. If the circuit is a bigger one with several components it is much more difficult.
3. To overcome this, standardized symbols of electric components are used to draw the circuit diagrams.

7th Class Science Textbook Page No. 89

Question 20.
Isn’t it so easy to draw like this?
Answer:
It is easy to draw a circuit by using symbols of electric components than realistic components. .

Question 21.
What difference do you find between circuit diagrams A and B?

Answer:

1. We observe that the bulb in circuit ‘A’ is not glowing and in circuit ‘B’ it is glowing.
2. We can also see the switch is in OFF mode in circuit diagram A and it is in ON mode in circuit diagram B.
3. Circuit diagram ‘A’ represents open circuit, where as circuit diagram ’B’ represents closed circuit.

7th Class Science Textbook Page No. 90

Question 22.
Is it possible to connect more than one bulb or one cell in an electric circuit?
Answer:
Yes, it is possible.

Question 23.
What happens if we connect more bulbs or cells in an electric circuit?
Answer:

1. There are two ways to connect more bulbs or cells in an electric circuit they are parallel and series connections.
2. In parallel connection electricity has more than one path where as in series connection only one path.
3. If the number of cells are connected in series the brightness of the bulbs enhanced where as in series the brightness of bulb remains same.

Question 24.
Have you observed a large number of bulbs used in decorations of marriage functions, festivals etc.?
Answer:

1. Yes, I have observed a large number of bulbs used in decorations of marriage functions, festivals etc.
2. All the bulbs are connected one after one that means in series.

Question 25.
What happens when we connect two cells and two bulbs in the same path?
Answer:

1. If we connect two cells and two bulbs in the same path, it is called series connection.
2. The brightness of the bulbs increased.

7th Class Science Textbook Page No. 92

Question 26.
Where can we observe these type of connections? (Series & Parallel)
Answer:

1. We can use series connection of cells in torch light, toys, remotes, wall clocks,radio etc.
2. We can use parallel connection of cells for a long – lasting battery life.

Question 27.
Do you know how several electric devices are connected in your home? Did you observe any pattern in their connections?
Answer:
If All the electric devices in our house are connected in parallel.

7th Class Science Textbook Page No. 93

Question 28.
Where can we observe these types of connection?
Answer:
We use series connection of bulbs for decoration purpose, parallel connection of bulbs in house hold connections.

7th Class Science Textbook Page No. 94

Question 29.
Naime the electrical devices used to produce heat?
Answer:
Electric iron box, electric heater, geyser, grills, electric cooker etc. are the electrical devices used to produced heat.

Question 30.
Have you ever used an iron box to iron your clothes? How does it produce heat?
Answer:

1. Electric iron box contains the coil of wire (filament) which produce heat, when electricity passed through it.
2. It is called heating effect of electricity.

Question 31.
Which electric appliances work on the principle of heating effect of electricity?
Answer:
1) Electric stove, 2) Electric room heater, 3) Electric iron box, 4) Electric kettle, 5) Electric cooker, 6) Water heater, 7) Geyser, 8) Hair dryer, etc. are working on the principle of heating effect of electricity.

7th Class Science Textbook Page No. 95

Question 32.
1) How does a fan work?
2) What makes the fan to rotate?
3) What is the principle involved in it?
Answer:

1. Fan works on the principle of magnetic effect of electricity.
2. The magnetic force, which is produced due to the flow of electricity through a wire (coil) makes the fah to rotate.
3. The principle, magnetic effect of electricity is involved in it.

7th Class Science Textbook Page No. 96

Question 33.
Which electric appliances work on the principle of magnetic effect of electricity?
Answer:
1) Electric fan, 2) Electric bell, 3) Electric motor, 4) Loud speaker, 5) MRI machines, 6) Generators, 7) Metal detectors, 8) Mobile phones, 9) Mixer grinders, etc. work on the principle of magnetic effect of electricity.

Question 34.
Have you seen the electric meter in your house? What do you find in the meter?
Answer:
I find reading of consumed electricity in units.

Question 35.
What does the term ‘one unit’ mean?
Answer:
1 unit = 1000 watt = 1 K.W.H.

Question 36.
How is the usage of electricity measured?
Answer:
Usage of electricity is measured in KWH (unit).

7th Class Science Textbook Page No. 98

Question 37.
What is an electric shock and when does it occur?
Answer:

1. An electric shock occurs when a person comes into contact with an electrical source.
2. Electricity flows through a portion of the body causing a shock.

Think & Respond

7th Class Science Textbook Page No. 85

Question 1.
Now a days we are using rechargeable torchlights, bulbs, mobile phones and fens. Think and discuss with your classmates about the working of these electric devices and the cells used in diem.
Answer:

1. A cell is made up of three parts, a cathode, an anode and an electrolyte (a chemical).
2. A cell works by connecting its stored chemical energy, into electrical power
3. One the electrolyte of the cell is used up it doesn’t work further in non – rechargeable cells (Alkaline cells).
4. Electrons (negative charges) travel from an anode to a cathode until the anode is considered empty or dead.
5. A rechargeable cell, a charger can reverse the electron flow again to restore at the anode. This is called charging.
6. This reversing process depends upon the electrolyte used in the cell.
7. Normal cells do not contain such type of electrolytes to reverse the charge.
8. But, the cells like NiMH (Nickel – Metal Hydride), Lithium – ion are capable of reversing the charge when charged it for number of times.
9. This type of rechargeable batteries are used in rechargeable torch lights, bulbs, mobile phones and fans.

7th Class Science Textbook Page No. 92

Question 2.
a) What happens if more cells are connected in a series?
b) Is there any restriction on the number of cells in a circuit for a given bulb?
Answer:
a) If more cells are connected in a series, voltage increases in the circuit. That means the strength of the current in the circuit increases.

b) When we will join lot of cells in a circuit, then the bulb will not be able to handle the large amount of energy supplied to it. Hence, the bulb may damage.

7th Class Science Textbook Page No. 95

Question 3.
Do all home appliances produce heat when electricity passes through them?
Answer:

1. Yes, all home appliances produce heat when electricity passes through them.
2. But the amount of heat produced depends on the material of conductor, such as length, thickness and nature of it.

7th Class Science Textbook Page No. 96

Question 4.
Is it possible to create permanent magnets using the magnetic property of electric current? Think and discuss with your classmates and make notes on this.
Answer:

1. Electromagnets are not permanent magnets because they lose the property of magnetism when the circuit is open.
2. A permanent magnet has a magnetic field all the time unless it is heated.
3. But electromagnet doesn’t retain its magnetism all the time, without current.

7th Class Science Textbook Page No. 98

Question 6.
Why don’t we use wet stick to push away a person when he get electric shock? Think and discuss with your friends.
Answer:

1. Wet stick contains some amount of water throughout it.
2. Water is a good conductor of electricity (ofcourse, pure water does not pass current).
3. If we touch the person to push away from the electric wire, the current passes through the water into our body.
4. It causes to get electric shock to us also.
5. So, we should not use wet stick to push away a person when he get electric shock.
6. We should use dry stick only to do that.

Activities and Projects

Question 1.
Collect any manual of electric equipment. Read the information in detail and answer the following questions.
A) When was it manufactured and how long can we use it?
B) How many stars are given to it?
C) Is it working on the basis of magnetic or heating effect?
Answer:
I Read the manual of a washing machine.
A) It was manufactured on 8^th March 2020.
B) It was given 5 stars.
C) It is working on the bases of both magnetic effect (motor) and heating effect (in built heater).

Question 2.
Find out the electric meter readings for 3 months in your house. Record your observations. Ask your teacher about how electricity bill is paid.
Answer:

Question 3.
Make a pamphlet on “Save electricity, don’t waste it”. Display it on the wall magazine?
Answer:

Question 4.
Collect last month’s electricity bills from your friends or neighbours houses and record the data. Advise them to change their ordinary bulbs with CFL bulbs. Again collect the electricity bilis of next month and observe the differences between the two bills. Discuss your observations with your friends and suggest better bulb.
Answer:
Observation sheet (Student Activity).

Conclusion :
After replacing ordinary bulbs with CFL/LED bulbs the consumption of electricity is reduced and Bill amount is saved.

Question 5.
If anyone around you has suffered an electric shock, collect the information along with their feelings and know about CPR. Record your observations in your note book and discuss with your friends.
Answer:
Observation sheet (Student Activity).

Activities

Activity – 1

Question 1.
If you open a dry cell, what do you observe?
(OR)
What do you observe inside the cell?
(OR)
Explain the structure of a cell with an activity.
(OR)
Describe the constru-ction of a dry cell.
(OR)
Describe the various components in a dry cell and their functions.
Answer:

1. Take a cell used in torch light and open it with the help of your teacher.
2. The cell consists of a container made of zinc metal. The container works as the negative terminal (- ve).
3. A carbon rod with a metal cap works as a positive terminal 0 ve>
4. The positive and negative terminals are called electrodes.
5. The carbon rod is surrounded by a mixture of carbon powder and a chemical called ammonium chloride. This mixture acts as an electrolyte.
6. The cell is sealed from the top.

Activity – 2

Question 2.
How do you make an own cell?
(OR)
Can you make a cell? If you can write the procedure.
(OR)
Write the procedure of making a cell using lemon.
Answer:
Material required: Zinc plate, Copper Plate, A small bulb or LED, Connecting wires and Lemon or Orange, crocodile clips-4.

Procedure:
Take a Lemon and insert a Zinc plate and a Copper plate into it as shown in the fig. These plates act as electrodes and the juice inside the fruit acts as electrolyte. Connect two terminals of the bulb to zinc and copper plates using connecting wires.

We observe that the bulb will glow as electricity was produced using chemical energy present in the lemon.

Activity – 3

Question 3.
Write an activity two observe the brightness of bulb in the following situations.
1) One cell and one bulb.
2) Two cells in series and one bulb.
3) Two cells in parallel and one bulb.
(OR)
How is the brightness of a bulb when it connected to a circuit with cells which are connected i) in series and ii) in parallel? Explain with an activity.
Answer:
Situation-1
Material required :
Dry cell -1, Small bulb-1 (torch light bulb or LED), Switch and Connecting wire.

Procedure:
Take a dry cell, small bulb or LED and a switch. Connect them in a simple circuit using copper wire as shown in given fig. Switch ON and observe the brightness of light. ,

Situation-2 (Cells connected in series) :
Material required :
Dry cells -2, Small bulb-1 (torch light bulb or LED), Switch and Copper wire.

Procedure:
Take two dry cells, small bulb and a switch. Connect them using a copper wire as shown in the fig. Switch ON and observe the brightness of light. Remove one cell and observe the condition of bulb.

Situation-3 (Cells connected in parallel) :

Material required :
Dry cells -2, Small bulb -1 (torch light bulb or LED), Switch and Copper wire.

Procedure:
Take two electric cells small bulb or LED and switch. Connect them using copper wire as shown in fig.

Switch ON and observe the brightness of bulb.Remove one cell and observe the condition of bulb.Record your observations in the above three situations in the given table.

From the table, if a number of cells are connected in series the brightness of the bulb isenhanced. If one of the cells is removed, the circuit becomes open and the bulb will not glow.If a number of cells are connected in parallel the brightness of the bulb remains same. Evenlf one of the cells is removed, the circuit remains same and the bulb will glow as usual.

Activity – 4

Question 4.
Write an activity to show the brightness of the bulbs when two bulbs are connected in series and in parallel.
Answer:
Situation-1
Materials required:
Dry cell -1, Small bulb-1 (torch light bulb or LED), Switch and Connecting wire.

Procedure :
Take a dry cell, small bulb or LED and switch.Connect them in a simple circuit using copper wireas shown fig.. Switch ON and observe the brightness of light.

Situation-2 (Bulbs connected in series):
Materials required:
Electric cell -1, Small bulbs -2 (torch light bulb or LED), Switch and Copper wire.

Procedure :
Take two small bulbs or LED’s, cell and switch.

Connect them using copper wire as shown in fig. Switch ON and observe the brightness of the bulbs. Remove one bulb and observe the condition of another bulb.

Situation-3 (Bulbs connected in Parallel):
Materials required:
Electric cell -1, small bulb -2 (torch light), Switch, Copper wire.

Procedure:
Take two small bulbs, a cell and a switch.Connect them using copper wire as shown in fig. Switch ON and observe the brightness of the bulbs.

Remove one bulb and observe the condition of another bulb.

From the table,if a number of bulbs are connected in series the brightness of the bulb is reduced. If one of the bulbs is removed or broken, the circuit becomes open and the second bulb will not glow. If the number of bulbs are connected in parallel the brightness of the bulb remains same. Even if one of the bulb Is removed or broken, the circuit remains same and the bulb will glow as usual, but the battery drains faster.

Activity – 5

Question 5.
Write an activity to know about beating effect of electric current.
(OR)
What happens if Garment is passed through a Nichrome wire? Explain with an activity.
(OR)
How do von show the heating effect of electricity through an activity?
Answer:
Materials required:
Electric cell, switch. Iron nails-2, wooden board, connecting wires, 10 cm of Nichrome wire.

Procedure :
Construct a circuit using electric cell, switch, connecting wires and iron nails in series connection. Insert the iron nails in the wooden board. Keep the switch in OFF position. Take Nichrome wire and tie it between the iron nails as shown in fig.

Observations :
Now switch ON the circuit for one minute, and switch it OFF. Now, touch the Nichrome wire, (don’t hold Nichrome wire for a long time.) You will observe that the Nichrome wire gets heated up when electricity passed through it. The production of heat due to the flow7 of electricity through a wire is called Heating Effect of Electricity.

Activity – 6

Question 6.
Write an activity to know about magnetic effect of electric current.
(OR)
How do you make an electromagnet?
(OR)
How do you prepare an electromagnet?
Answer:
Material required:
Battery, Switch Iron nail (nearly 8 cm). Insulated copper wire (50 cm) and small pins.

Procedure:
Take an iron nail and wound the insulated copper wire tightly around the nail. This iron aaS works as a coil. The two ends of the coiled copper wire are connected to a battery and a switch in series connection as shown in fig. (Switch roast be in OFF position. Place some pins near the iron nail and switch ON the circuit.

We observe that, when we switched, on the circuit, all pins ding to the end of the iron nail. This indicates coiled copper wire around nail acts as magnet when electricity passes through it. It means the coiled copper wire around the nail acts as an electromagnet.

When we switched off the circuit, immediately all the pins fall from the iron naS. This indicates that coiled copper wire does not act as a magnet when no electricity7 passes through the circuit

Magnetic effects produced in a coil due to the passing of electricity in the coil is called magnetic effects of electricity.

SCERT AP 7th Class Science Study Material Pdf 5th Lesson Motion and Time Textbook Questions and Answers.

AP State Syllabus 7th Class Science 5th Lesson Questions and Answers Motion and Time

7th Class Science 5th Lesson Motion and Time Textbook Questions and Answers

Improve Your Learning

I. Fill in the blanks.

1. Units of speed is _____
2. If a body covers equal distances in equal intervals of time, it is said to be _____ motion.
3. 60 minutes = _____ seconds. (3600)
4. Average speed = total distance travelled / _____
5. ISRO stands for _____
6. Geostationary satellites are used for _____ purpose.
Answer:
1. m/s
2. uniform
3. total time taken to travel
4. Indian Space Research Organization
5. Communication

II. Choose the correct answer.

1. The correct relation between speed, distance and time is
a) Speed = distance / time
b) Speed = time / distance
c) Time = speed/ distance
d) Distance = speed / time
Answer:
a) Speed = distance / time

2. What is common in the following?
Motion of the propeller of a flying helicopter, the hands of a watch, motiob of a giant-wheel.
a) All are examples of translatory motion
b) All are examples of oscillatory motion
c) All are examples of rotatory motion
d) a & c
Answer:
c) All are examples of rotatory motion

3. Which of the following is not an oscillatory motion?
a) Motion of the hammer of an electric bell.
b) Motion of your hands while running.
c) Motion of a child on a see – saw.
d) Motion of a horse pulling a cart.
Answer:
d) Motion of a horse pulling a cart.

4. Which of the following statements is not correct?
a) The basic unit of time is second.
b) Every object’s motion is Uniform.
c) 1 km/h = 5/18 m/s.
d) Speed is expressed in km/h.
Answer:
b) Every object’s motion is Uniform.

III. Matching

Answer:

IV. Answer the following

Question 1.
The distance between two stations is 240km. A train takes 4 hrs to cover this distance. Calculate the speed of the train m/s.
Answer:
The distance between two stations = 240 km
Time taken to cover this distance = 4 hrs
Speed of the train = distance / time
= 240/ 4 km/hrs
= 60 km/hrs

This is the speed of the train in km/hrs,
to convert it into m/s….

Question 2.
Can an object possess translatory and rotatory motion at the same time? Give an example.
Answer:

1. Yes. An object can possess both translatory and rotatory motions at the same time.
2. When we observe the motion of a cycle tyre moving in a straight line, all the parts of tyre moves in the same direction of cycle so, we can say it is in translatory motion.
3. If we observe the rolling of cycle tyre, it move in a curved (circular) path about a iron rod in the middle of the wheel as an axis. So, we can say it is in rotatory motion.
4. In this way the cycle tyre moving in a straight line possesses both translatory, and rotatory motions.

Question 3.
In a sewing machine used by tailors, mention the type of motion of its parts when it runs, a) the wheel b) the needle c) the cloth
Answer:

Question 4.
Write the motion of different parts of a bicycle while it is in motion, a) the wheels b) the cycle chains c) the pedal with its arm d) the movement of the rider along with the bicycle.
Answer:

Question 5.
John tied a stone to a string and whirled it around. What type of motion do you observe?
Answer:
When a stone is tied to a string and whirled it around, it move in a circular path around the hand. That means the stone fallows a curved path with respect to the hand as a fixed centre or axis of rotation. So it is said to be in rotatory motion.

Question 6.
What are Uniform and Non-Uniform motions? Give four examples for each type of Motions.
Answer:
i) Uniform motion : “If a body covers equal distances in equal intervals of time, it is said to be in uniform motion”.
Ex: 1. Hands of a clock
2. Revolution of Earth
3. A train going at a steady speed
4. The blades of a fan

ii) Non-uniform motion: If a body covers unequal distances in equal intervals of time, it is said to be in non-uniform motion.
Ex : 1. Movements of butterfly in a garden
2. The motion of a car in a city traffic
3. An aircraft while landing
4. Running of athletes in a marathon

Question 7.
Your friend told you the motion of rocket is fast motion. Will you agree? How can you decide whether the motion of a body is slow or fast?
Answer:

1. Yes. I agree with him. Because rockets move with the speed of 12 km per second. Its very high speed.
2. The distance travelled by an object in a given interval of time can help us to decide whether it is faster or slower.
3. The distance travelled by an object in a unit time is called as its Speed.
4. Speed = Distance travelled / Time taken to travel.
5. Units of speed is meter per second (m/s) or kilometre per hour (Km/h).
6. 1 Km / h = 5/18 m/s
7. The object moving with less speed is slow and more speed is fast. Thus we can decide whether the motion of a body is slow or fast using its speed.
8. At a particular instant of time, we can find speed of a vehicle using speedometer.

Question 8.
How can you appreciate the clocks and watches in measuring or estimating time?
Answer:

1. Clocks and watches are helpful to us in measuring or estimating time.
2. They help us in scheduling our works properly.
3. They help us in attending the works on time by displaying the time.
4. With out clocks and watches its very difficult to estimate the time.
5. Sometimes they are used to make a loud alert signal at a specified time to make us wake up or recall a work.
6. Some times they are helpful in measuring the time also.
7. Now a days they are.available in some other gadgets like mobile phone also.
8. Thus they become an essential and integral part of our life.

7th Class Science 5th Lesson Motion and Time InText Questions and Answers

7th Class Science Textbook Page No. 68

Question 1.
What do you observe from the picture?

Answer:
You can see the movement of cars, buses, train, boat, clouds, birds and minute hand in the clock etc. On the other side we can see the bridge, buildings, road, hill and the clock tower which are not moving.

7th Class Science Textbook Page No. 69

Question 2.
Do all these things move alike?
Answer:
No.

Question 3.
What makes the objects move and moving object to come to rest?
Answer:
Force makes the objects move and moving object to come to rest.

Question 4.
What do we call the motion of a train moving in a straight line?
Answer:
Translatory motion.

Question 5.
Is the forward movement of birds and the movement of its wings same?
Answer:

1. Not same.
2. Forward movement of birds is a translatory motion and wing movement is an oscillatory motion.

Question 6.
How do you decide whether any object is in motion or at rest?
Answer:

1. Motion is a common experience in our life.
2. We feel an object is in rest when it is not changing its position and we fee! an object is in motion when it is changing its position with respect to the surroundings.

Question 7.
Are all these trees, buildings, electric poles, etc. really in motion?
Answer:
No.

Question 8.
Which one do you feel is moving, passenger in the bus or tree?
Answer:
Passenger.

Question 9.
Which one do you feel is moving, tree or your co-passenger?
Answer:
Tree.

Question 10.
Why is it so?
Answer:
Motion and rest are relative terms and ‘hey are relative to the observer. We feel an object is at rest when it is not changing, its position. We feel an object is in motion When it is changing its position with respect to the surroundings.

7th Class Science Textbook Page No. 70

Question 11.
Have you ever played carrom board? What is the reason for movement of coins when we hit them with a striker?
Answer:
The force applied by the striker on the coins is the reason for movement of coins.

Question 12.
How force effects the motion?
Answer:
Force can change the position of motion to rest, of vice – versa.

7th Class Science Textbook Page No. 71

Question 13.
What did your friend apply to make the ball move?
Answer:
Force (muscular force).

Question 14.
What did you apply to change the direction of the ball?
Answer:
Force (muscular force).

Question 15.
What did your friend apply to stop the moving ball?
Answer:
Force (muscular force).

Question 16.
What can we call the length of path that an object moves from one place to another?
Answer:
Distance.

Question 17.
Ouserve the picture, Kavitha can reach her school in two ways. From A, B roads which path will you suggest her to reach the school early? You will suggest the shortest distance pat*” which is road A.

Answer:
Road A

7th Class Science Textbook Page No. 72

Question 18.
What can we call the duration of motion of the object when it is moving from one place to another place?
Answer:
Time to travel

Question 19.
How can we call the period between starting and ending incidents (events) in a running race.
Answer:
Time.

Question 20.
How do we measure or estimate time?
Answer:
Clocks (watches) are the most common time measuring devices.

7th Class Science Textbook Page No. 73

Question 21.
Are all the motions same?
Answer:
No, all the motions are not same.

Question 22.
How many types of motions are there?
Answer:
Motion is of three types :

1. Translatory motion
2. Rotatory motion
3. Oscillatory motion.

Question 23.
Have you played with a toy car? How does it move if you push it forward?
Answer:
It moves in translatory motion.

Question 24.
Do all the parts of bus like wheels, headlights, windows etc., move through the same distance from building ‘A’ to building ‘B’?
Answer:
Yes, all parts of the bus moves along the bus.

Question 25.
Is the direction of motion of bus along a straight line or a curved line?
Answer:
In a straight line.

7th Class Science Textbook Page No. 74

Question 26.
Can you give some more examples of motion in which all points of moving body move through same distance in the same direction?
Answer:
Examples:

1. Coconut falling from a tree.
2. Movement of lift.
3. Car travelling on a straight road.
4. Movement of water from the tap.

Question 27.
If all the parts of a body move along the curved path. What type of motion it is?
Answer:
Rotatory motion.

Question 28.
Observe the following diagrams.

1) Do you find any similarity in the above motions?
2) What is the path of motion of each part of the body that moves? ’
Answer:

1. In the above situations, the parts of the objects move in a curved path with respect to a fixed centre or a fixed axis.
2. They are in rotatory motion with circular path.

7th Class Science Textbook Page No. 75

Question 29.
Can objects have simultaneous Translatory and Rotatory motions?
Answer:
Yes. The cycle tyre moving in a straight line possesses both translatory and rotatory motions.

Question 30.
Have you played with a see-saw? How does it move?
Answer:

1. See – saw moves in up and down direction with a fixed point.
2. This type of motion is called oscillatory motion,

Question 31.
How does the needle of swing machine moves?
Answer:
The needle of a sewing machine moves in ‘to and fro’ motion or back and forth motion.

7th Class Science Textbook Page No. 76

Question 32.
Which similarity do you find in the moving parts of the above instruments?
Answer:
All are moving in ‘to and fro’ motion.

Question 33.
Is the direction of motion constant? Are they moving in the same path again and again?
Answer:

1. The direction of motion of the objects changes alternatively along the same path about a fixed point. Hence the direction of motion of the object not constant.
2. Yes, they are moving in the same path again and again.

Question 34.
Does all motions take same time to cover same distance?
Answer:
No.

7th Class Science Textbook Page No. 77

Question 35.
Do you find any relation between distance and time?
Answer:
Yes, distance divided by time give speed the objects.

Question 36.
How to calculate the average speed?

Question 37.
Is there any other method to express the motion of objects?
Answer:
Yes, we can express the motion of objects by graphs.

7th Class Science Textbook Page No. 78

Question 38.
Have you seen launching of rocket in T.V, how does it move?
Answer:

1. Rockets move in translatory motion.
2. The exhaust gases coming out of the engine’s nozzle at the high speed push the rocket forward.

Question 39.
Do you know which Indian organization is working for it?
Answer:
ISRO (Indian Space Research Organization) is working for it.

Question 40.
Where do these rockets are launched?
Answer:
Rockets are launched at Satish Dhawan Space Centre (SDSC – SHAR), Sriharikota, Andhra Pradesh.

7th Class Science Textbook Page No. 80

Question 41.
Have you noticed what happens if you let the air out of a inflated balloon?
Answer:
The air comes out of balloon in one direction and the balloon moves on the opposite direction with the same speed.

Question 42.
Have you observed the movement of Diwali rocket cracker?
Is there any similarity between movements of rocket cracker and real rocket?
Answer:

1. Diwali rocket cracker takes flight, when it is fired.
2. Motion of the actual rocket is similar to it.

Question 43.
Have you ever feel wonder of knowing weather report in advance?
Answer:
Yes, weather report forecasting in advance is possible because of artificial satellites.

Question 44.
How google maps give route maps between two places?
Answer:

1. Google maps is a internet based application to show maps and roots between two places.
2. They map our location with the pictures and data provided by artificial satellites.
3. By using artificial intelligence, they integrate the information and give route maps between two places.

Activities and Projects

Question 1.
Use a tennis ball or cricket to make it translatory motion, rotatory motion, and oscillatory motion. Write a note on it and discuss with your friends.
Answer:

1. I took a tennis ball and throwed it towards my friend to catch it. The motion showed . by ball is translatory motion.
2. Spun the ball on my finger. It shows rotatory motion.
3. Now it is rolled over the ground towards my friend. It shows both translatory and rotatory motions.
4. Now tied this ball to a thread and moved forward and backward. This shows the oscillatory motion.

Question 2.
Make a water clock or a sand clock and use it to know time.
Answer:

1. I took two, clear plastic bottles that are the same size and shape.
2. Took the caps off, glued them together, and let the glue dry.
3. I Punched a hole through the middle of the glued-together caps.
4. Screwed the cap onto the first bottle, just like we normally would.
5. Filled the second bottle with dry sand.
6. Screwed the empty bottle onto the sand-filled bottle.
7. Tested my sand timer by turning it upside down to know whether the sand is flowing smoothly from one bottle to the next or not.
8. Marked the time on the bottles at various levels of sand by observing the time using stop watch.
9. Wrapped some tape around the neck.
10. My sand clock is ready to use.

Activities

Activity – 1

Question 1.
Classify the objects given in the figure based on motion and rest and what is your inference?

Answer:

Inference:

1. “An object is said to be in motion if it changes its position with respect to its surroundings.”
2. “An object is said to be at rest if there is no change in its position with respect to its surroundings.”

Activity – 2

Question 2.
How do you show that force is required to change the object from rest into motion, to change its direction and even to change from motion to rest?
Answer:

Take a football and go to your school ground with your friends. Stand in a triangle shape as shown in the figure.Ask your friend to kick the ball in your direction. You pass the ball to another friend. Ask him to stop that ball. Now answer the following questions.
1) What did your friend apply to make the ball move?
Answer:
Force

2) What did you apply to change the direction of the ball?
Answer:
Force

3) What did your Mend apply to stop the moving ball?
Answer:
Force

You all applied muscular force with your legs to do so.

From the above observation we can say that force is required, to change the object from rest into motion, to change its direction and even to change from motion to rest.

Activity – 3

Question 3.
Write any activities to explain the distance and displacement.
Answer:
Try to measure the distance between your bench to the place where MDM is been served in your school.

How much it is? (Student has to measure and answer on their own)

Have you ever used the google maps to know the distance and direction of your desti-nation?

Now, know the distance between your native place to district head quarter using google maps?

How much it is? _____ km. (Student has to measure and answer on their own)

Observe the picture, Kavitha can reach her school in two ways. From A, B roads which path will you suggest her to reach the school early? You will suggest the shortest distance path which is road A.

From the above activity and examples, we can say that when an object travels from one place to another, the length of the path can be measured and it gives the distance between the two places. When an object travels along the straight-line path from one place to another place, it will reach faster. The length of the straight-line path is the shortest distance between two places, called displacement.

Activity – 4

Question 4.
Conduct 100 meter running race with the help of your physical education teacher. Use stop watch from lab or mobile phone to measure time taken to complete the race by each student. Fill the table given below.

Answer:

[Note : Fill in the table with your records)

Activity – 5

Question 5.
Consider the following situation. Robert and Kamala measured the distance trav¬elled while coming to school and the time taken to cover that distance. Their data is shown in the Table. You can draw a graph by following the steps given below:

Answer:
1) Draw two perpendicular lines to represent the two axic anti mark them as OX and OY. Mark OX as time axis and OY as distance axis.

2) Choose a scale to represent distance and time on the graph.
Time : 1 min = 1 cm.
Distance : 50 m = 1 cn

3) Mark values for the time and the distance on the respective axis according to the scale you have chosen.

Now you have to mark the points on the graph paper to represent each set of values and, join al! the points on the graph. This is the distance-time graph for the given motion.

4) If the distance-time graph is a straight line, it indicates that the object is moving with a constant speed. However, if the speed of the object keeps changing, the graph can be of any other shape. From the distance-time graph we can find the speed of object.

From the distance-time graph we can find the speed of object.