AP State Syllabus AP Board 7th Class Science Important Questions Chapter 5 Temperature and Its Measurement
AP State Syllabus 7th Class Science Important Questions 5th Lesson Temperature and Its Measurement
7th Class Science 5th Lesson Temperature and Its Measurement Important Questions and Answers
What are the different clothes we wear in different seasons?
- We wear woolen and dark coloured clothes during winter when it is cold outside.
- Woolen and dark coloured clothes keep us warm.
- We prefer to wear light coloured cotton clothes when it is hot.
- They give us a feeling of coolness.
- It is a wonder why a particular type of cloth is suitable for a particular season.
When rice is being cooked you observe the plate on the rice bowl jumps! Why is it happening?
The heat energy converts water into steam and the pressure of steam throws away the lid.
Have you observed water boiling in a vessel with a lid on it? What do you notice? How can you establish that heat is a form of energy?
- We know that boiled water is being converted to water vapour.
- The volume of the water vapour increases.
- The increased volume of vapour tries to go out. In this process it tries to lift the lid up.
- We need energy to lift any object. This energy comes from the heated water.
- Water gets the energy from the heat of the fire. Thus heat is a form of energy:
What is heat?
- We feel hot when we sit in sunlight or near fire. We feel cold when we put a piece of ice on our palm.
- We know that heat is a form of energy that is transferred from an object at higher temperature to one at lower temperature.
- When we stand in the sun or near fire, heat energy enters our body and we feel hot. When ice is put on our palm, heat energy moves from our body to the piece of ice.
- That’s why we feel cold.
- “The energy which makes an object appear hot or cold is called heat.”.
What happens in the following?
a) Rub your palms together. How do you feel?
b) Have you ever observed that iron becomes hot when it is beaten with a hammer?
c) Take a soapnut seed. Rub it on a stone and touch it. How do you feel?
In above cases mechanical energy is converted into heat energy.
Explain the terms ‘heat’ and ‘temperature’.
- If we stand close to fire, we feel warm.
- When a warm object is placed close to a cooler object, heat energy moves from the warmer object to the cooler one until both objects attain the same temperature.
- Often we think that heat and temperature are the same things. This is wrong.
- Temperature is a measure of the heat energy in a body which indicates the ability of a body to give heat to another body or absorb heat from another body.
- We use thermometers to measure temperature.
What are the properties of mercury?
Properties of Mercury:
- Its expansion is uniform. (For equal amounts of heat it expands by equal lengths.)
- It is opaque and shining.
- It does not stick to the sides of the glass tube.
- It is a good conductor of heat.
- It is easily available in pure state.
Write the properties of alcohol.
Properties of Alcohol:
- It can record very low temperatures.
- Its expansion per degree Celsius rise in temperature is very large.
- It can be coloured brightly and hence is easily visible.
Who first designed the thermometer? What do you know about it?
- First thermometer was invented by Galileo in 1593 AD.
- In this thermometer air was used as the thermometric substance as air rapidly expands on heating and contracts on cooling.
- Further, the substance that is used in the thermometer has uniform expansion or contraction with the rise or fall in temperature.
Do you find any difference in temperature of air in shadow and in the sun?
Measure temperature of air using a thermometer. What will you do to keep a thermometer in close contact with air?
- The temperature of air will be more as it receives heat directly from the sun and from reflected radiations.
- The temperature in the shadow will be relatively less as only reflected radiant heat reaches there.
Is there any difference in temperature with variation of time or place?
There is difference in temperature with variation of time or place.
Why do you use an umbrella in the hot sun during summer?
To avoid direct heat radiations from the sun.
Write a note on the variations of temperature on different occasions and at different places over the globe?
- In Lybia (Africa) on a particular day in the year 1922, it became so hot that the temperature of air even in shade was as high as 58 °C.
- At some places (Rentachintala of Guntur District) in Andhra Pradesh, the maximum temperature of air sometimes reaches 48 °C and more.
- When it is so hot we feel extremely uncomfortable as the normal temperature of the human body is 37 °C.
- The lowest temperature in the world has been measured in Antarctica where it once went down to about -89 °C.
- The minus sign is used for temperature which is less than 0 °C. Water freezes at 0 °C, just think how cold -89 °C must be.
- In winter when the atmospheric temperature around us becomes 15 °C – 20 °C we begin to feel cold.
What is a clinical thermometer ? Describe its construction.
- Thermometer which is used to find out the temperature of our bodies is called Clinical Thermometer.
If we observe Thermometer carefully. There are two types of scales marked on the clinical thermometer one that starts with 35 degrees and ends at 45 degrees is Celsius scale. While the other that starts with 95 degrees and ends at 110 degrees is the Fahrenheit scale.
- We see a kink in the capillary near the bulb.
- This kink prevents Mercury level from falling on its own.
What is the value of one division on the fahrenheit scale on thermometer?
- Note the temperature difference indicated between the two bigger marks.
- Also note down the number of divisions between these marks.
- Suppose two consecutive bigger marks differ by one degree and there are five divisions between them.
- Then one small division reads
1/5 = 0.2 °F
Describe how do we use a clinical thermometer.
- We should wash the thermometer preferably with an antiseptic solution.
- Holding it firmly by the end and give it a few jerks. These jerks will bring the level of mercury down. Ensure that it falls below 35 °C (95 °F).
- Now we should plape the thermometer under our tongue or arm pit.
- After one minute, we have to take the thermometer out and note the reading. It tells our body temperature.
How can you decide whether one has fever or not?
The normal temperature of human body is 37°C (98.6°F). If one has body more than 98.6°F can consider as fever.
Write a note on a) Thermister thermometer and b) Digital thermometer.
a) Thermister thermometer:
It is available in market to measure the human body tempera¬tures, particularly for infants and children.
b) Digital thermometer:
- There is a lot.of concern over the use of Mercury in thermometer.
- Mercury is a toxic substance and is very difficult to dispose of if a thermometer breaks.
- These days digital thermometers are also available which do not use Mercury.
What precautions are suggested in using a clinical thermometer?
- We are advised not to use a clinical thermometer for measuring the temperature of any object other than human body.
- Also we are advised to avoid keeping it in the sun or near a flame.
Measure the temperature of a person with clinical and digital thermometers.
Are the temperature readings same or different? Explain your observations.
The temperature readings in both clinical and digital thermometers are the same.
What is value of one small division on the Celsius scale?
Reading the Celsius scale on thermometer.
- Temperature difference is indicated between two bigger marks.
- Between these two bigger marks divisions are there.
- Suppose two consecutive bigger marks differ by one degree and there are 10 divisions between them then one small division reads
1/10 = 0.1°C
∴ The value of one small division on the Celsius scale is 0.1 °C.
How do you measure the temperature of other objects?
- To measure the temperature of other objects there are other thermometers.
- One such thermometer is known as the laboratory thermometer used to measure temperature of water.
- Six’s maximum and minimum therometer is used to measure maximum and minimum temperatures of a day.
Can you make use of laboratory thermometer like a clinical thermometer?
- We should take some hot water in a beaker, dip thermometer in it for one minute.
- Record the temperature while the thermometer is in water.
- Take out the thermometer from water. Observed the mercury thread carefully.
- As there is no kink in the laboratory thermometer mercury falls down in the glass tube of its own when taken out of the water. So we cannot use a laboratory thermometer like a clinical thermometer.
Measure the temperature of different students by touching them and noting in the clinical thermometer.
Make sure that you have cleaned the thermometer before each measurement.
Compare the values in the table after completion of recording.
a) What do you observe in the table?
b) Are the estimated temperature and measured temperature same?
c) Is the body temperature of every person 37 °C (98.6 °F)?
d) What is the average body temperature of your friends?
The average body temperature of a large number of healthy persons is known as normal temperature (98.6 °F).
The student is advised to do this work as a project work.
Some of the objects are given in the table. Mark these objects as hot or cold. What is your conclusion?
- We see that some objects are cold and some are hot.
- We also know that some objects are hotter than others while some are colder than
- To decide which object is hotter than the other, and which object is colder than the other.
- We need a reliable method to decide the hotness/coldness of an object.
- Generally, hotness or coldness is expressed in terms of temperature.
- Temperature is a measure of the degree of hotness or coldness of an object.
How can find out the hotness or coldness of a substance by touch? Explain.
- By touching with our hands, we can guess whether a cup of milk is still worth sipping or has become too cold, whether milk is hot enough for making curds etc.
- But estimating temperature with our hands can, sometimes mislead or confuse us.
- Take some cold water, luke-warm water and hot water in three different vessels.
- Immerse your left hand in the cold wa¬ter vessel and right hand in hot water vessel simultaneously. Wait for two or three minutes.
- Take off both your hands and dip them in the luke-warm water vessel.
- Though both hands are in the same glass of water, one hand feels it cold and the other feels it hot! Look how our hands are confused!
- We can not exactly decide the hotness/coldness of a substance just by touching it?. It is not possible to guess the hotness of a substance only on the basis of feel/touch.
- It is certain that water in different tubs has different degrees of hotness which can¬not be exactly determined simply by touching.
How do we establish by experiment that liquids expand due to heat?
- We should take a flat bottom flask and fill it with coloured water.
- Fix a cork, having a capillary tube, in the mouth of flask such that level of water is as shown (fig).
- We should place the flask in a metal trough.
- We should pour boiling hot water into the trough and carefully observe the level of coloured water. The level rises.
- If we take the flask out of the trough and keep it outside for some time, the level of coloured water decreases.
- In the above activity we see that water expands on heating and contracts on cooling.
Record your observations in the following.
Do the above observation independently.
Did you ever bathe with cold water during winter? What happens?
- I have taken bathe with cold water during winter.
- My body shivered with chill.
What do you do to protect yourself from cold?
- I wear woolen and dark coloured clothes to protect myself from cold.
- I will cover my body with a blanket to protect myself from cold in the night.
How do you get hot water in winter?
By heating water, I get hot water in winter.
Generally we heat water to get hot water. How do you heat water? What sources do you use?
By converting electrical energy, chemical energy and mechanical energy into heat we heat water. We use electric heaters, gas stoves and solar heaters to heat water.
Give examples of conversion of energy from one form to another.
- Different kinds of energies can be converted to heat.
- In the same way heat energy can be converted to other forms of energy.
- We have heard that in a thermal power station, heat energy is converted to electrical energy.
- In a steam engine, heat energy is converted to mechanical energy which helps in moving the engine.
- In electrical heater electrical energy, in gas stove chemical energy and in solar heaters solar energy are converted to heat.
What are the liquids used as thermometer liquids?
- Mercury is used as liquid for indicating temperature in thermometers.
- Apart from Mercury we also use alcohol as thermometer liquid.
Describe the construction of a thermometer with a neat diagram.
- At one end of the tube we observe a bulb. It is filled with Mercury.
- The other end of the tube is sealed after removing air from it.
- We find a scale which is marked to express temperature in degree Celsius.
- We read the temperature with the help of these markings.
- The readings range from 0° to 100°
- This arrangement of the marks is called scale of temperature.
- All thermometers are based on the fact that matter expands on heating.
Draw a neat diagram of Six’s maximum and minimum thermometer. What is its importance.
1) The maximum (highest) and minimum (lowest) temperatures of a day are measured by a thermometer called the Six’s maximum-minimum thermometer.
How do you use a thermometer? Write an example.
- To find the temperature of an object, the bulb of the thermometer needs to be in close contact with that object.
- Watch the shiny line of mercury in the tube. .
- The highest point on the scale, at which the rise of mercury stops, shows the temperature of the object.
- Example: To find the temperature of your palm, place the bulb of thermometer in contact with palm for two minutes and see the mercury rise.
- When mercury stops rising and its level becomes steady, note the position of its upper end.
- This is the temperature of your palm.
If markings on thermometer are wiped out, how do we create new markings?
- Take some ice in a beaker. Immerse a thermometer in ice for two minutes. Mark the Mercury level. Now let the ice melt.
- The level of Mercury remains same while ice melts. This means that temperature is constant.
- This constant temperature at which ice melts is called melting point of ice and mark it 0 °C.
- Take some water in a beaker. Immerse the thermometer in it and start heating the water. It will start boiling while getting converted into steam.
- Mercury level starts rising and reaches a point beyond which it doesn’t rise. Mark the level of mercury at this point.
- Observe the constant level at which Mercury stays while water is boiling, this constant temperature is called boiling point of water. We mark the level of mercury at this point as 100 °C.
- Thus temperature at which ice melts or water boils is constant. These values are fixed as 0 °C and 100 °C respectively. Like water, all substances in pure form melt and boil at certain fixed temperatures.
- To create a scale, we need two fixed points. Let us choose the melting point (0 °C) and boiling point (100 °C) as two fixed points for the scale of thermometer. Now divide the distance between these two points on the thermometer into 100 equal parts.
- Each of the 100 equal parts represents 1 °C. We further divide 1 °C into 10 small divisions. It can be read as 1/10 = 0.1 °C.
Feel the body temperature of some of your friends by placing your hand on their forehead. Estimate the temperature and record it in the table.
The student is advised to do this with the help of the teacher.
How do you note the temperature of water taken in a beaker?
- Take some tap water in a beaker.
- Dip the thermometer in water so that the bulb is immersed in water but does not touch the bottom or side of the beaker.
- Hold thermometer vertically, wait till the mercury thread becomes steady.
- Note the reading. That is the temperature of water at that time.
Observe the diagram and answer the following questions.
- What is the aim of the experiment?
- Write down the apparatus required.
- What are your observations?
- Where do you find this type of phenomenon in your daily life?
- Liquids expand on heating.
- A flat bottom flask, cork, coloured water, metal trough, boiling hot water.
- Water expands on heating and the level in coloured water is increased.
- We can observe this phenomenon in the thermometer in our day to day life.
Read the paragraph and answer the following questions:
Heat is a type of Energy. It is transferred from hot object to cold object. We know the hotness and coolness of an object due to the transformation of energy. It is called “Heat”. If you want to heat the water with electric heater, Electric Energy is turned into Heat Energy. If you heat the water on gas stove, Chemical Energy is turned into Heat Energy.
i) What is Heat?
ii) How is heat transferred from one object to other?
iii) Which equipment is used to turn Electric Energy into Heat Energy?
iv) When we heat water on the gas stove, which energy is turned into Heat Energy?
i) It is a form of energy. The energy which makes an object appear hot or cold is called heat.
ii) Heat flows from an object at high temperature to another at lower temperature.
iii) Electric heater.
iv) Chemical energy.
What questions would you ask the doctor to clarify your doubts on the usage of the thermometer?
- Why do we use thermometer in our daily life?
- Why is mercury used in thermometers?
- How do we measure the temperature in thermometer?
- How many types of scales are marked on the thermometer?
Read the paragraph given below and answer the following questions.
Temperature is a measure of the heat energy in a body. We use thermometers to measure temperature. Mercury is a good conductor of heat and is a liquid at room
temperature. It is used in most thermometers. In some thermometers, alcohol is used. Alcohol can record very, low temperatures.
i) What is temperature?
ii) Name the device used to measure the temperature.
iii) Name the liquid used commonly in the thermometers.
iv) Name the liquid used in thermometers to measure low temperature.
i) Temperature is a measure of heat energy in a body.
ii) The device used to measure temperature is thermometer.
iii) Mercury is the liquid used in thermometers.
iv) Alcohol is used in thermometers to measure low temperature.
Observe the table and answer the following questions.
i) Name the month and date when the minimum temperature was recorded.
ii) On which date was the maximum temperature recorded?
iii) Between which two consecutive months, the difference in temperature was the highest?
iv) In which month people could most likely have used air-conditioner to get relief from heat?
i) 1st January, 2019.
ii) 15th May, 2019
iii) April and May
iv) In May month