Conductors and insulators

Why are circuit wires made of metal? Build a tester (Activity 3.11): a cell and a lamp with two wire ends left free. Touch the free ends together and the lamp glows. Now touch them to the two ends of different objects: spoons, coins, cork, rubber, glass, keys, pins, a plastic scale, wood, aluminium foil, a candle, a needle, cardboard, paper and pencil lead.

The lamp glows for some materials only.

Silver, copper and gold are the best conductors. Wires are made mainly of copper, because it costs less and there is plenty of it.

We need both. Wires, switches and the pins of plugs and sockets are conductors. Insulators such as plastic, rubber and ceramic cover the wires, plug tops and switches, to protect us from shocks. An electrician wraps black insulating tape round bare wire ends, and a screwdriver has a plastic handle so your hand stays safe.

Caution. Your body is a conductor. Current through your body can cause severe injury or even death. Never touch switches or plugs with wet hands, never use electrical things in wet places, and never use a wire with damaged covering or a broken plug.

One more difference. The electricity from a cell or battery is direct current (DC) and runs small devices. The electricity in a wall socket comes from power plants; it is alternating current (AC), much stronger, and runs larger appliances. That is why you only experiment with cells.