NCERT Solutions - Chemical Effects of Electric Current Class 8 Notes | EduRev

Science Class 8

Created by: Dr Manju Sen

Class 8 : NCERT Solutions - Chemical Effects of Electric Current Class 8 Notes | EduRev

The document NCERT Solutions - Chemical Effects of Electric Current Class 8 Notes | EduRev is a part of the Class 8 Course Science Class 8.
All you need of Class 8 at this link: Class 8

Question: 1. Fill in the blanks

(a) Most liquids that conduct electricity are solutions of, _______,______and ______.

Answer: Acids, Bases and Salts

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

Answer: Chemical

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

Answer: Negative

NCERT Solutions - Chemical Effects of Electric Current Class 8 Notes | EduRevFig: Electroplating of copper.

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

Answer: Electroplating


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

Answer: The deflection in the magnetic needle is observed, when the electric current flows through the wounded wire. Hence, it means the solution is a good conductor of electricity. This is the reason magnetic needle shows deflection when the free ends of a tester are dipped into a solution.


Question: 3. Name three liquids, which when tested in the manner shown in the figure, may cause the magnetic needle to deflect.

NCERT Solutions - Chemical Effects of Electric Current Class 8 Notes | EduRev

Answer: Acid solution, Salt solution, Solution of a base


Question: 4. The bulb does not glow in the setup shown in the figure. List the possible reasons. Explain your answer.

NCERT Solutions - Chemical Effects of Electric Current Class 8 Notes | EduRev

Answer: The lists of possible reasons for the bulb not glowing are:
(i) The circuit might be incomplete.
(ii) The bulb might be fused.
(iii) Liquid in the beaker might be non-conducting.
(iv) Insufficient charge of battery which might be responsible for bulb not glowing.


Question: 5. 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) liquid A is better conductor than liquid B.


Question: 6. Does pure water conduct electricity? If not, what can we do to make it conducting?

Answer: Pure water does not conduct electricity. By dissolving some salt, such as common salt, pure water can be made a conductor of electricity.


Question: 7. 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: Water is good conductor of electricity. Therefore, firemen shut off the main electrical supply for the area before using of water hoses in the case of fire to prevent them from getting electric shock.


Question: 8. 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: Since, seawater contains more salts dissolved in it, thus in the case of seawater, compass needle of the tester deflects more than the drinking water.


Question: 9. Is it safe for the electrician to carry out electrical repairs outdoors during heavy downpour? Explain.

Answer: No, it is not safe for the electrician to carry out electrical repairs outdoors during heavy downpour because the rain water contains dissolved salts. This makes rain water a good conductor of electricity; hence, it might cause electrical shock to electrician.


Question: 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: Many impurities get dissolved in the rain water while it comes to the ground. Due to the presence of these impurities, rainwater conducts electricity. This explains Paheli’s observation.


Question: 11. Prepare a list of objects around you that are electroplated.

Answer: The following is a list of objects around me which are electroplated:
(i) Cars, buses, etc. are electroplated with chromium to give them shiny appearance.
(ii) Artificial jewellery items are either silver or gold plated.
(iii) Door handles, metal items, etc. are zinc plated.
(iv) Cans are tin plated.
(v) Iron used in building constructions is coated with zinc to prevent corrosion and rusting of iron.


Question: 12. The process that you saw in Activity 14.7 is used for purification of copper. A thin plate of pure copper and a thick rod of impure copper are used as electrodes. Copper from impure rod is sought to be transferred to the thin copper plate. Which electrode should be attached to the positive terminal of battery and why?

Answer: Electrode of impure copper is connected with the positive terminal. Because pure copper metal, which is positively charged, from positive terminal is deposited over the negative terminal of thin copper after dissolving in the solution. 

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