Chapter Review:

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• The passage of an electric currernt through a conducting liquid causes chemical reaction. The resulting effects are called  chemical effects of currents. 

• Which allow electric current to pass through them, are good conductors of electricity.

• Which do not allow electric current to pass through them easily, are poor conductors of electricity.

• Most liquids that conduct electricity are solutions of acids, bases and salts.

• Two wires are called leads.

• Distilled water is free of salts and is a poor conductor.

• When salt is dissolved in distilled water, we obtain salt solution. This is a conductor of electricity.

• Oxygen bubbles formed on the electrode connected to the positive terminal of the battery and hydrogen bubbles formed on the other electrode.

• The process of depositing a layer of any desired metal on another material by means of electricity is called electroplating. 

• Chromium has a shiny appearance. It does not corrode. It resists scratches.

Exercise

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1. Fill in the blanks

(a) Most liquids that conduct electricity are solutions of , ______________ and ______________.

(b) The passage of an electric current through a solution causes ______________ effects.

(c) If you pass current through copper sulphate solution, copper gets deposited on the plate connected to the terminal of the battery.

(d) The process of depositing a layer of any desired metal on another material by means of electricity is called .

Answer:

(a) acids, bases, salts, (b) chemical, (c) negative, (d) electromagnet.

2. When the free ends of a tester are dipped into a solution, the magnetic needle shows deflection. Can you explain the reason?

Answer:

Yes, it is because the solution conducts electricity.

3. A tester is used to check the conduction of electricity through two liquids, labeled 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. You would conclude that

(i) liquid A is a better conductor than liquid B.

(ii) liquid B is a better conductor than liquid A.

(iii) both liquids are equally conducting.

(iv) conducting properties of liquid cannot be compared in this manner.

Answer:

(i) Liquids A is better conductor than liquid B.

4. Does pure water conduct electricity? If not, what can we do to make it conducting?

Answer:

Pure water does not be conduct electricity. It can be made conducting if acid, base or salt is dissolved in it.

5. In case of a fire, before the firemen use the water hoses, they shut off the main electrical supply for the area. Explain why they do this.

Answer:

The water used to extinguish fire, have lot of minerals and dissolved salts, which make it conducting. Before throwing it water into the burning houses, the burning houses, the mains of electricity of the area is turned off because then the water may conduct huge current and firemen get electrocuted.

6. A child staying in a coastal region tests the drinking water and also the seawater with his tester. He finds that the compass needle deflects more in the case of seawater. Can you explain the reason?

Answer:

The impure water is conductor of electricity. Sea water contains more impurity than drinking water. Therefore, sea water conducts more electricity than the drinking water. That is why, compass needle deflects more in case of sea water.

7. Is it safe for the electrician to carry out electrical repairs outdoors during heavy downpour? Explain.

Answer:

When it rains heavily, the rain water dissolves many impurities from the atmosphere which makes is impure and hence conductive. The air too becomes humid with this water and behaves as a conductor to electricity. That is why, it is not wise for eletrician to do electrical repair work when it rains heavily, becuse he may get dreadful shock or even gets electrocuted.

8. Paheli had heard that rainwater is as good as distilled water. So she collected some rainwater in a clean glass tumbler and tested it using a tester. To her surprise she found that the compass needle showed deflection. What could be the reasons?

Answer:

Rain water is, of cource, as good as distilled water but, when it passe s through atmosphere, it dissolves a lot of dust, dirt and impurities and becomes conductive. So, when Paheli used a tester, its compass showed deflection. 

9. Prepare a list of objects around you that are electroplated.

Answer:

(i) Tap of water connection,

(ii) Parts of bicycle,

(iii) Body of cars, motor cycle ahd tractors,

(iv) Handle of the doors, etc.

10. Paheli had heard that rainwater is as good as distilled water. so, she collected some rainwater in a clean glass tumvler and tested it using a tested it using a tester. To her surprise she found that the compass needle showed deflection. What the compass needle showed deflection. What could be the reason?

Answer: Rain water is, of course, as good as distilled water but, when it passes through atmosphere, it dissolves a lot of dust, dirt and impurities and dissloves a lot of dust, dirt and impurities and become conductive. So, when paheli used a tester, its compass showed deflection.

 

 

Exercise

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1. Fill in the blanks

(a) Most liquids that conduct electricity are solutions of , ______________ and ______________.

(b) The passage of an electric current through a solution causes ______________ effects.

(c) If you pass current through copper sulphate solution, copper gets deposited on the plate connected to the terminal of the battery.

(d) The process of depositing a layer of any desired metal on another material by means of electricity is called .

Answer:

(a) acids, bases, salts, (b) chemical, (c) negative, (d) electromagnet.

2. When the free ends of a tester are dipped into a solution, the magnetic needle shows deflection. Can you explain the reason?

Answer:

Yes, it is because the solution conducts electricity.

3. A tester is used to check the conduction of electricity through two liquids, labeled 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. You would conclude that

(i) liquid A is a better conductor than liquid B.

(ii) liquid B is a better conductor than liquid A.

(iii) both liquids are equally conducting.

(iv) conducting properties of liquid cannot be compared in this manner.

Answer:

(i) Liquids A is better conductor than liquid B.

4. Does pure water conduct electricity? If not, what can we do to make it conducting?

Answer:

Pure water does not be conduct electricity. It can be made conducting if acid, base or salt is dissolved in it.

5. In case of a fire, before the firemen use the water hoses, they shut off the main electrical supply for the area. Explain why they do this.

Answer:

The water used to extinguish fire, have lot of minerals and dissolved salts, which make it conducting. Before throwing it water into the burning houses, the burning houses, the mains of electricity of the area is turned off because then the water may conduct huge current and firemen get electrocuted.

6. A child staying in a coastal region tests the drinking water and also the seawater with his tester. He finds that the compass needle deflects more in the case of seawater. Can you explain the reason?

Answer:

The impure water is conductor of electricity. Sea water contains more impurity than drinking water. Therefore, sea water conducts more electricity than the drinking water. That is why, compass needle deflects more in case of sea water.

7. Is it safe for the electrician to carry out electrical repairs outdoors during heavy downpour? Explain.

Answer:

When it rains heavily, the rain water dissolves many impurities from the atmosphere which makes is impure and hence conductive. The air too becomes humid with this water and behaves as a conductor to electricity. That is why, it is not wise for eletrician to do electrical repair work when it rains heavily, becuse he may get dreadful shock or even gets electrocuted.

8. Paheli had heard that rainwater is as good as distilled water. So she collected some rainwater in a clean glass tumbler and tested it using a tester. To her surprise she found that the compass needle showed deflection. What could be the reasons?

Answer:

Rain water is, of cource, as good as distilled water but, when it passe s through atmosphere, it dissolves a lot of dust, dirt and impurities and becomes conductive. So, when Paheli used a tester, its compass showed deflection. 

9. Prepare a list of objects around you that are electroplated.

Answer:

(i) Tap of water connection,

(ii) Parts of bicycle,

(iii) Body of cars, motor cycle ahd tractors,

(iv) Handle of the doors, etc.

10. Paheli had heard that rainwater is as good as distilled water. so, she collected some rainwater in a clean glass tumvler and tested it using a tested it using a tester. To her surprise she found that the compass needle showed deflection. What the compass needle showed deflection. What could be the reason?

Answer: Rain water is, of course, as good as distilled water but, when it passes through atmosphere, it dissolves a lot of dust, dirt and impurities and dissloves a lot of dust, dirt and impurities and become conductive. So, when paheli used a tester, its compass showed deflection.

Additional Questions With Solutions

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Ques: What is electroplating?

Ans: The process of depositing a layer of any desired metal on another material by means of electricity is called electroplating.

Ques:What do you understand by chemical effects of currents?

Ans: The passage of an electric currernt through a conducting liquid causes chemical reaction. The resulting effects are called  chemical effects of currents.

Ques: Solution of which Substances  conduct electricity?

Ans: Acid ,base and salt.

Ques: If you pass current through copper sulphate solution, On which terminal of battery copper gets deposited ?

Ans: Negative terminal.

Ques: What is called the process of depositing of a layer of any desired metal on another material by means of electricity?

Ans: Electroplating.

Ques: Does Pure water conduct electricity? If no, What can we do to make it conductor?

Ans: No Pure water does not conduct. There is melt acid, base or salt to make it conductor.

  

Additional Questions With Solutions

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Ques: What is incident ray?

Ans:The light ray, which strikes any surface, is called the incident ray.

Ques: What is reflected ray?

Ans: The ray that comes back from the surface after reflection is known as the reflected ray.

Ques: Write the law of reflection.

Ans:

(i) Angle of incidence is always equal to the angle of reflection.

(ii) The incidence ray, the normal at the point of incidence and the reflected ray all lie in the same plane.

Ques: What is diffused or irregular reflection?

Ans: When all parallel rays reflected from a plane surface are not parallel, the reflection is known as  diffused or irregular reflection.

Ques: What is regular reflection?

Ans: Reflection from a smooth surface like that of a mirror is called regular reflection.

Ques: What is called the phenomenon, in an image formed by a mirror the left of the object appears on the right and the right appears on the left?

Ans: This phenomenon is called lateral inversion.

Ques: Write the use of Periscopes.

Ans:Periscopes are used in submarines, tanks and also by soldiers in bunkers to see things outside.

Ques: What is Kaleidoscope? Write its one use.

Ans: Kaleidoscope is an idea or a device that is made to combine the mirrors at an angle to one another to get number of images. It is used to make numerous beautiful patterns.