# AP Board 8th Class Physical Science Important Questions Chapter 9 Electrical Conductivity of Liquids

AP State Syllabus AP Board 8th Class Physical Science Important Questions Chapter 9 Electrical Conductivity of Liquids

## AP State Syllabus 8th Class Physical Science Important Questions 9th Lesson Electrical Conductivity of Liquids

### 8th Class Physical Science 9th Lesson Electrical Conductivity of Liquids 1 Mark Important Questions and Answers

Question 1.
Why do we use LED in the tester instead of a bulb?
LED glows even when a very weak current is passing through the circuit. Thus, it helps in testing flow of electricity in conductors when meager current is passing through the circuit.

Question 2.
Why do we use LEDs as indicators in electrical appliances?
LEDs glow even with a very small current passing through them. So they are used as indicators in electrical appliances like mobile phones, televisions, transformers, etc. to indicate whether the device is working or not.

Question 3.
What is meant by good conductors of electricity?
Some materials allow electric current pass through them easily. They are called good conductors of electricity.

Question 4.
What is meant by bad conductors of electricity?
The materials that do not allow current to pass through them are called bad conductors of electricity.

Question 5.
Why distilled water is poor conductor of electricity?
Distilled water does not dissociate easily to form ions. So there is no availability of charged particles for passage of electricity. So it behaves like a bad conductor of electricity.

Question 6.
Why water used at our homes is a good conductor of electricity?
The water that we get from sources such as taps, hand pumps, wells and ponds is not pure like distilled water. It contains some salts and minerals dissolved in it. This makes the water used at our homes a good conductor of electricity.

Question 7.
What is electrolytic cell?
The cell which convert chemical energy into electric energy is called electrolytic cell.

Question 8.
A child staying in a coastal region tests the drinking water and also the sea water with his tester. He finds that compass needle deflects more in the case of sea water. Can you explain the reason?
The reason is sea water is very good conductor of electricity when compared with drinking water due to more dissolved salts.

Question 9.
Is it safe for electrician to carry out electrical repairs outdoor during heavy down pour?
No, because it makes electrical appliance which he repairs become wet and also rainy water is good conductor of electricity due to dissolved minerals and salts. So to avoid electric shock it is advised to carry out electric repairs indoor during heavy downpour.

Question 10.
A tester is used to check conduction of electricity through two liquids labelled A and B. It is found that the bulb of the tester glows brightly for liquid A while it glows very dimly for liquid B. What is your conclusion?
Liquid A is better conductor than liquid B.

Question 11.
When the free ends of a tester are dipped into a solution, the magnetic needle shows deflection. Can you explain the reason?
The solution is a good conductor of electricity and also when we dipped the tester into the solution due to chemical effect it produces electricity and it behaves like an electrolytic cell and also current carrying tester behaves like a magnet and shows deflection.

Question 12.
What is the main threat to environment from electroplating factories?
In the electroplating factories the disposal of the used conducting solution is a major concern. It is a polluting waste. So it is the main threat to environment from electroplating factories.

Question 13.
Why should we have to deposit nickel or chromium on iron?
Iron which is easily corroded by atmospheric air, moisture and carbon dioxide are coated with deposits of nickel or chromium which are most resistant to such corrosion.

### 8th Class Physical Science 9th Lesson Electrical Conductivity of Liquids 2 Marks Important Questions and Answers

Question 1.
What is the name given to wires attached to LED. How these wires are connected to a battery?
There are two wires called leads attached to an LED. One lead is slightly longer than other.

While connecting to the LED to the circuit, the longer lead is always connected to the positive terminal of the battery and the short lead connected to the negative terminal of the battery.

Question 2.
What are the requirements for fine coating in electroplating process?

1. The object to be electroplated should be free from greasy matter.
2. The surface of the article should be rough so that the metal deposited sticks permanently.
3. The concentration of the electrolyte should be so adjusted as to get smooth coating.
4. Current must be the same throughout.

Question 3.
a) When we pass current through a copper sulphate solution having copper plate and iron key connected to a battery and tap key in series by closing tap key. What is deposit on iron key?
b) If the key is to be coated with zinc or aluminium instead of copper, what changes do we need to make the above experiments?
a) There is red mass of copper deposited on iron key.
b) If we want to coat aluminium or zinc or iron then, we have to take electrolyte is like aluminium sulphate or zinc sulphate and the positive electrode is aluminium or zinc.

Question 4.
Name three liquids which when tested in the manner shown in figure may cause the magnetic needle to deflect.
In order to deflect the needle the liquid must be a good conductor of electricity. So we have to take liquids like lemon juice, vinegar solution, salt solution.

Question 5.
The bulb does not glow in the set up shown in figure. List the possible reasons. Explain your answer.

1. The wires are not properly connected so the circuit may be open.
2. The liquid taken in the vessel may be a bad conductor of electricity which does not allowing the passage of current.

Question 6.
Give two examples for electrolyte.
Electrolyte is a solution of substance through which current can pass. The examples of electrolyte solutions are NaC/ solution, CaCl2 solution.

Question 7.
If the key is to be coated with aluminium instead of copper,what changes do we need to make in the experiment of coating on iron key with copper?
Changes we need to make are:

1. Anode should be aluminium.
2. The electrolyte solution must be salt solution of aluminium that is aluminium chloride or aluminium sulphate solutions.

Question 8.
Is plastic coated by the process of electroplating? Why?
No. Plastic cannot be coated on a metal by using electroplating. Plastic does not act as an electrolyte. So electrolysis process is not possible with plastic which is main criteria for electroplating. So plastic cannot be coated on a metal by the process of electroplating.

Question 9
What are the requirements for fine coating in electroplating process?

1. The object to be electroplated should be free from greasy matter.
2. The surface of the article should be rough so that the metal deposited sticks permanently.
3. The concentration of the electrolyte should be so adjusted as to get smooth coating.
4. Current must be the same throughout.

Question 10.
In case of a fire, before the fire men use the water, they shut off the main electrical supply for the area. Explain why they do this.
Fire men use water to put out fire. Water containing dissolved salts is a good conduc¬tor of electricity. If fire men pour water on fire the electrical appliances near the fire may be wet if anybody touches those appliances they may have electric shock. In order to avoid people to get electric shock due to wet electrical appliances the fire men shut off electrical supply before they use water.

Question 11.
We get some items made from iron wire in which iron wire is coated with plastic. Is plastic coated by the process of electroplating? Why can plastic not be coated on a metal by the process of electroplating?
No. Plastic cannot be coated on a metal by using electroplating. The reason is plastic being a carbon polymer does not dissociate into ions. So it does not allow passage of current. So it does not act as an electrolyte. So electrolysis process is not possible with plastic which is main criteria for electroplating. So plastic cannot be coated on a metal by the process of electroplating.

### 8th Class Physical Science 9th Lesson Electrical Conductivity of Liquids 4 Marks Important Questions and Answers

Question 1.
Prepare a table having various material used at home classifying as good conductors or poor conductors and their use.

 Material used at home Good conductor/ poor conductor Use 1) Copper Good conductor Wires, electrical appliances 2) Iron Good conductor Electrical wires, electrical appliances 3) Aluminium Good conductor Wires, electrical appliances 4) Plastic Poor conductor Handles of electrical appliances, electrical insulating material 5) Wood Poor conductor Handles of electrical appliances

Question 2.
What are the uses of electrolysis in daily life?
The uses of electrolysis:

1. Electroplating: To avoid rusting of iron it is coated with nickel or chromium by electrolysis.
2. Gold covering works: Ornaments made of cheap metal like copper can be coated with gold using electrolysis.
3. Metallurgy: Pure metals can be extracted from minerals and ores using electrolysis.
4. Electrolysis: It is used in electrical printing and to produce gramphone records.

Question 3.
Collect the information from various sources on the applications of electroplating in daily life and prepare a note on that.
Uses of electroplating:

1. Metals like iron are coated with deposits of nickel or chromium to prevent rusting.
2. Machinery parts are often chromium plated to protect them from corrosion and at the same time to give them good polish.
3. Electroplating is also used in repairing worn out parts of machinery.
4. Electroplating is also done for ornamentation and decoration purposes.
5. Processed food items are preserved in tin coated iron cans by electroplating method.
6. Zinc coated iron by electroplating method is used for bridges and in automobiles.

Question 4.
Test the conductivity of liquids given below and fill the table.

 Material Compass needle show deflection Yes / No Conductor / Insulator Lemon juice Honey Milk Vinegar Tap water Vegetable oil

 Material Compass needle show deflection Yes / No Conductor / Insulator Lemon juice Yes Conductor Honey No Insulator Milk No Insulator Vinegar Yes Conductor Tap water Yes Conductor Vegetable oil No Insulator

Question 5.
Why does chromium is used for electroplating? Why the objects which have chromium plated are not made of chromium itself?

1. Chromium has a shiny appearance does not corrode and resist scratches.
2. However chromium is expensive and may not be possible to make the whole object out of chromium.
3. So the object is made from a cheaper metal and only a coating of chromium is done over it.

### 8th Class Physical Science 9th Lesson Electrical Conductivity of Liquids Important Questions and Answers

Question 1.
Name the process of coating a metal on another metal. Draw a neat diagram related to this process. Label the parts.