Class 8 Science Textbook Solution

Effects of Electric Current – Class 8 Science Textbook Solution

 

 Chapter 14 Chemical Effects of Electric Current
 
1. Fill in the blanks:
1.    Most liquids that conduct electricity are solutions of _______ and _______
2.    The passage of an electric current through a solution causes _______ effect.
3.    If you pass current through copper sulphate solution, copper gets deposited on the plate connected to the _______ terminal of the battery.
4.    The process of depositing a layer of any desired metal on another metallic object, by means of electricity, is called _______
Answer:

1.    Most liquids that conduct electricity are solutions of acids, bases, and salts.
2.    The passage of an electric current through a solution causes a Chemical effect.
3.    If you pass current through copper sulphate solution, copper gets deposited on the plate connected to the negative terminal of the battery.
4.    The process of depositing a layer of any desired metal on another material by means of electricity is called electroplating.
 
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 and the solution plays the role of a small cell.
 
3. Name three liquids, which when tested in the manner shown in Fig.14.9, may cause the magnetic needle to deflect.

Answer: Lemon water, vinegar, tap water.
 

4. The bulb does not glow in the setup shown in Fig. 14.10. List the possible reasons. Explain your answer.

Answer: The bulb does not glow because:
•    The solution may not be a good conductor of electricity.
•    The electricity in the circuit was very little.
•    The bulb may be fused.
•    The cells may be used up.
•    The connections of wires may be loose.
 

5. A tester is used to check the 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. 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) Liquid A is a better conductor than liquid B.
 
6. Does pure water conduct electricity? If not, what can we do to make it conducting?
Answer:
Pure water does not conduct electricity. It can be made conducting by adding acid, base or salt into it.
 
7. In case of fire, before the firemen use the water hoses, they shut off the main electrical supply of the area. Explain why they do this.
Answer:
Water is a good conductor of electric current. So, the firemen shut off the electric supply before spraying water to save themselves and other people from electrocution.
 
8. A child staying in the 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
: Drinking water has been processed and purified before supplying it to the houses. Many salts and minerals have been removed from it, so it has decreased its conductivity. On the other hand, seawater is rich in salts, and other acids, and basic substances, that is why it is a better conductor of electricity and deflects the needle more than the purified drinking water.
 
9. Is it safe for the electrician to carry out electrical repairs outdoors during heavy downpours? Explain.
Answer:
No, it is highly dangerous to carry on electric repairs in water, as water is a good conductor of electricity. It can cause electrocution.
 
10. 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:
While it rains, the raindrops get mixed with the suspended particles of the air. So, they do not remain pure. It becomes a mixture of salts and other impurities thus shows the conduction of electricity.
 
11. Prepare a list of objects around you that are electroplated.
Answer:
The object that is electroplated are:
•    Taps of water connection.
•    Parts of the bicycle.
•    Body (parts) of cars, motorcycle, and tractors
•    The handle of the doors, etc
•    Artificial jewellery
•    Metallic almirahs.
•    Buckles of clothes and belts, etc.
•    Utensils
•    Buckets.
 
12. The process that you saw in Activity 14.7 is used for the purification of copper. A thin plate of pure copper and a thick rod of impure copper are used as electrodes, Copper from the impure rod is sought to be transferred to the thin copper plate. Which electrode should be attached to the positive terminal of the battery and why?
Answer:
The impure copper rod should be attached to the positive terminal because the free copper will get drawn towards the negative terminal to be get deposited, so the copper from the impure rod will get collected in the pure copper plate.
Chemical Effects of Electric Current Additional s and Answers
 
1. Why it is very dangerous to operate an electrical appliance with wet hands?
Answer:
If someone operates electrical appliances with wet hands, there is a chance of getting electrocuted.
 
2. Define conductors.
Answer:
Materials which allow an electric current to pass through them are called conductors, e.g., aluminium copper, etc.
 
3. Do liquids also conduct electricity?
Answer:
Yes, tap water, lemon juice, and acids are some of the liquids which conduct electricity.
 
4. When is the circuit of the tester complete and when is it not complete?
Answer
: When the liquid between the two ends of the tester allows the electric current to pass, the circuit of the tester becomes complete. The current flow in the circuit and the bulb glows. When the liquid does not allow the electric current to pass, the circuit of the tester is not complete and the bulb does not glow.
 
5. What effect does the current product when it flows through the conducting solution?
Answer:
The passage of an electric current through a conducting solution causes chemical reactions. As a result, bubbles of gas may be formed on the electrodes. Deposits of metal may be seen on electrodes. Changes in colour of solutions may occur. The reaction would depend on what solution and electrodes are used. These are some of the chemical effects of the electric current.
 
6. What is electroplating?
Answer:
The process of depositing a layer of any desired metal on another material by means of electricity is called electroplating.

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