NCERT Science Textbook, Class VIII Chapter 14: Chemical Effects of Electric Current

NCERT Textbook Exercise Questions (Important Only)

Q.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 ____ effect.

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 metallic object, by means of electricity, is called _______.

Ans: (a) acids, bases, salt (b) chemical (c) negative (d) electroplating.

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

Ans: Electric current produces magnetic effect which causes deflection of the magnetic needle of a compass. So, when the free ends of a tester are dipped into a solution which is a good conductor of electricity, the needle shows deflection.

Q.4: The bulb does not glow in the set-up shown in figure. List the possible reasons. Explain your answer.

Ans: There could be several possible reasons for not glowing of the bulb:

(i) The bulb may be fused.

(ii) Even after replacing the bulb if it does not glow, then the connection may be loose or faulty.

(iii) Even after checking and repairing the connections if the bulb does not glow that means the solution does not conduct electricity.

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

Ans: NO, pure water does not conduct electricity. Some salt can be added to make it conductor.

Q.8: A child staying in a coastal region tests the drinking water and also the sea water with his tester. He finds that his tester needle deflects more in case of sea water. Can you explain the reason?

Ans: Drinking water has been processed and purified before supplying to the houses. Many salts and minerals have been removed from it, which will reduce its electricity conducting property considerably. On the other hand the sea water is rich in salts, and other acids and basic substances, that is why is a better conductor of electricity and deflects the needle more than the purified drinking water.

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Short type Questions with their Answers

Q.1: What are conductors?

Ans: Substances which allow the electric current to pass through them are called conductors.

Q.2: What are insulators?

Ans: Substances which does not allow electric current to pass through them are called insulators.

Q.3: Are liquids conductors of electricity?

Ans: Yes, some liquids are conductors of electricity e.g., lemon juice, vinegar, tap water etc.

Q.4: What are the metal rods dipped in liquids to which cells are attached called?

Ans: Electrodes.

Q.5: When we pass current through a conducting solution of water, which gas bubbles will appear near positively charged electrodes?

Ans: Oxygen.

Q.6: Name any chemical effect of electric current.

Ans: Electroplating.

Q.7: To which terminal of the battery the metal meant for electroplating is attached?

Ans: Negative terminal.

Q.8: In which direction does current flow?

Ans: From negative to positive terminal.

Q.9: Which gas will accumulate near negative electrode when electric current is passed through a conducting solution of water?

Ans: Hydrogen.

Long type Questions with their Answers

Q.1: What is LED, why is it the most preferable source of electricity?

Ans: The full form of LED is Light Emitting Diode. It is like a bulb which can glow even at a feeble current supply. Ordinary bulbs can not glow when the current supply is low. So they consume more current and are therefore, costly. Since LED consumes much lower electricity so, they are economical.

LEDs are available in many colours such as, red, green, yellow, blue etc. They find applications for many purposes like in traffic signals, on railway platforms for various indicators etc.

Q.2: How can you prove conducting properties of substances when the current is very small and bulb does not glow?

Ans: When current passing through a conductor is very small, the bulb won’t glow. In such cases we use magnetic compass to detect conduction of current.

Q.3: What is ‘Electroplating’? Describe.

Ans: Electroplating is the process of coating a desired metal on another metal surface using electric current. It is one of the most common applications of chemical effects of electrical current. Metallic plate and the substance requiring coating are dipped in conducting solution with conducting wires. The object to be coated is attached to the negative terminal. When electric current is passed through the solution, the compounds of the solution starts breaking and free metallic particles get deposited on the object at the negative terminal of battery. In this way we can get a coating of desired metal on any object by preparing suitable conducting solution and using suitable electrodes.

Q.4: Give some advantages of electroplating.

Ans: Electroplating is a very useful process and has many advantages:

1. It is used to coat metal surfaces with another metal having desired properties.

2. It saves certain metal surfaces from rusting, corrosion etc.

3. Coating of chromium on other metals give luster to objects and better corrosion resistance.

4. Cheap metals like iron, aluminium etc. can be coated with costly metals like silver, gold etc. to give them rich look as in case of artificial jewellary.

5. With the help of this process we can reactive metals like iron etc. less reactive after electroplating them with tin, zinc etc. to make them more useful for certain purposes.

One Response to “NCERT Science Textbook, Class VIII Chapter 14: Chemical Effects of Electric Current”

  1. tania Says:

    thanks so much it helped me so much……………………

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