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.
Answer
Sorting the objects of Table 3.3 by material gives a clean division:
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?
Answer
Yes. The metal inside carries the current; the plastic or rubber outside makes sure the current cannot reach our hands.
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.