CBSE · NCERT · Class 8 Science · Chapter 11

NCERT Solutions: Class 8 Science Chapter 11 - Chemical Effects of Electric Current

12 textbook Q&A12 verifiedFree Content

Chapter-wise NCERT intext questions and exercise answers for Chemical Effects of Electric Current, grounded in the official textbook.

Questions are taken verbatim from the NCERT textbook; answers were grounded against the chapter's content during generation. Items needing review are marked.
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Exercises 12
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1Exercises12 questions
Q.1Fill in the blanks about conducting liquids, chemical effects, copper sulphate and electroplating.v
Answer:

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

Q.2Why does the magnetic needle deflect when tester ends are dipped in a conducting solution?v
Answer:

The solution allows electric current to pass, and current in the tester wire produces a magnetic effect that deflects the needle.

Q.3Name three liquids that may cause the magnetic needle to deflect.v
Answer:

Lemon juice, vinegar and salt solution.

Q.4The bulb does not glow in a tester setup. List possible reasons.v
Answer:

The liquid may be a poor conductor, current may be too weak, the bulb may be fused, cells may be weak, or connections may be loose.

Q.5Tester bulb glows brightly for liquid A and dimly for liquid B. What follows?v
  1. i. liquid A is a better conductor than liquid B
  2. ii. liquid B is a better conductor than liquid A
  3. iii. both are equally conducting
  4. iv. conducting properties cannot be compared
Answer:

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

Q.6Does pure water conduct electricity? If not, how can it be made conducting?v
Answer:

Pure water is a poor conductor. Adding a small amount of salt, acid or base makes it conducting.

Q.7Why do firemen shut off main electrical supply before using water hoses?v
Answer:

Ordinary water conducts electricity. Shutting off supply prevents electric shock.

Q.8Why does seawater deflect the compass needle more than drinking water?v
Answer:

Seawater contains more dissolved salts, so it conducts electricity better.

Q.9Is it safe for electricians to repair outdoors during heavy rain?v
Answer:

No. Rainwater with dissolved salts conducts electricity and increases risk of electric shock.

Q.10Why did rainwater collected by Paheli deflect the tester needle though rainwater is said to be like distilled water?v
Answer:

Rainwater dissolves gases, dust and salts from air and containers, so it can conduct electricity.

Q.11List objects around you that are electroplated.v
Answer:

Chrome-plated taps, bicycle handles, artificial jewellery, tin-plated food cans, and gold- or silver-plated ornaments.

Q.12For copper purification, which electrode should impure copper be connected to and why?v
Answer:

The impure copper rod should be connected to the positive terminal. Copper dissolves from it into solution and deposits on the thin pure copper plate connected to the negative terminal.