Hinglish

Electrical Conductors and Insulators

Class 7 Science · Chapter 3: Electricity: Circuits and their Components · NCERT Curiosity section 3.4

Learn

Why are wires made of metal and covered in plastic? Ishaan makes a tester: a cell and a lamp with two free wire ends. Touching the ends together lights the lamp. Now he touches the ends to each object in turn.

With a key, a spoon, a coin, aluminium foil or a needle the lamp glows; with plastic, rubber, wood, glass, paper, wax or cork it stays off. Materials that let current flow easily are conductors (good conductors); materials that do not are insulators (poor conductors). Metals are conductors.

Silver, copper and gold conduct best; wires are mostly copper, which is cheaper and plentiful. Plastic, rubber and ceramics are insulators, so they cover wires, plugs and switches to protect us. Both kinds are needed: conductors carry current, insulators keep it where it belongs.

Caution: our body is a conductor. Current through it can cause severe injury or death. Never touch switches or plugs with wet hands, never use electrical things in wet places, and never use equipment with damaged insulation. Cells give DC; wall sockets give AC, which runs big appliances.

Explore: the conduction tester.

  1. Test each object and sort it.

Remember

  • Conductors (metals) let current flow; insulators (plastic, rubber, wood, glass) do not.
  • Insulators cover conductors for safety; our body conducts, so be careful.

Quick check

Why are electric wires made of copper?

  1. copper is a good, affordable conductor
  2. copper is an insulator
  3. copper is the lightest metal
  4. copper never gets hot
Answer

copper is a good, affordable conductor. Copper conducts very well and is cheaper and more plentiful than silver or gold.

Think about it

List objects at home that are only conductors, only insulators, and made of both.

One answer

Conductors only: steel spoon, key, nail. Insulators only: plastic bucket, rubber slipper, wooden spoon. Both: an electric iron, a plug, a screwdriver with a plastic handle, a wire.

Practice

Practise with fresh questions at three levels (easy, medium, hard), some answered hands-on, with hints and worked answers. Get 4 of your last 5 right to finish the topic.