NCERT Solutions for Class 7th Science Chapter 3 In-text Questions — Electrical Conductors and Insulators

Book page 36 Updated on2026-09-19

Q1.

Analyse your observations. Did the lamp glow for all materials?

Answer

No. The lamp glowed for some materials only.

That single observation carries the whole idea of the section:

Materials through which electric current can flow easily are called good conductors, or conductors of electricity.
Materials through which current cannot pass are called insulators, or poor conductors of electricity.

Why it happens: In a metal, some of the tiny charged particles are free to move through the whole piece, so they can carry current from end to end. In wood, plastic, glass or rubber the charged particles are held tightly in place and cannot travel, so no current flows.

Q2.

Based on the observations you have recorded in Table 3.3, conclude which materials are conductors of electricity and which are insulators. Note it in Table 3.3.

Table 3.3: Identifying Conductors and Insulators

S.No.	Object	Material it is made up of	Lamp glows (Yes/No)
1.	Stick	Wood	No
2.	Scale	Plastic
3.	Bangle	Glass
4.	Paper strip	Paper
5.	Candle	Wax
6.	Key	Metal
7.	Eraser	Rubber
8.
9.

Table 3.3, page 35 — the recording table for conductors and insulators.

Answer

Sorting the objects of Table 3.3 by material gives a clean division:

Conductors of electricity	Insulators (poor conductors)
Metals — key, coin, spoon, pin, sewing needle, aluminium foil	Wood — stick, wooden block
Pencil lead (graphite)	Plastic — scale, wire covering
	Glass — bangle
	Rubber — eraser, cork
	Paper and cardboard — paper strip
	Wax — candle

The main conclusion is that metals are conductors of electricity, and that is why they are used for making wires. Silver, copper and gold are the best conductors, but wires are mainly made of copper because it costs much less and is available in plenty.

Q3.

From Table 3.3, you would have also realised that plastic, rubber, and ceramics are electrical insulators. Have you now understood why wires are covered with those materials?

Table 3.3: Identifying Conductors and Insulators

S.No.	Object	Material it is made up of	Lamp glows (Yes/No)
1.	Stick	Wood	No
2.	Scale	Plastic
3.	Bangle	Glass
4.	Paper strip	Paper
5.	Candle	Wax
6.	Key	Metal
7.	Eraser	Rubber
8.
9.

Table 3.3, page 35 — the recording table for conductors and insulators.

Answer

Yes. The metal inside carries the current; the plastic or rubber outside makes sure the current cannot reach our hands.

Part of a device	Made of	Because
Wire core, switch contacts, plug pins, socket connectors	Conductors (copper, brass)	Current must flow through them
Wire covering, plug top, switch body, holder	Insulators (plastic, rubber, ceramic)	Current must not flow out of them

Why it happens: Our body is itself a conductor of electricity. Current passing through the body may cause severe injury or even death. The insulating cover is the barrier that stands between the current and the person holding the wire — which is why a wire with cracked or peeled insulation must never be used.

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