Current has a magnetic effect

At the school science exhibition, Mohini and Aakarsh saw their senior Sumana's model of a lifting crane. Instead of a hook it had an iron nail wrapped in wire and joined to a battery. When Sumana closed the circuit, the nail picked up iron paper clips like a magnet. When she opened it, the clips dropped. And there was no magnet in the model at all, only an electric circuit.

Try it (Activity 4.1). Make a switch as in Grade 7, put a cell in a holder, stretch a wire between two nails on cardboard so it sits just above the surface, and complete the circuit. Put a magnetic compass under the wire.

Switch ON: the compass needle turns away from where it was pointing. Switch OFF: it swings back. Do it a few times and it always happens.

You know from Grade 6 that a compass needle is a tiny magnet. It turns when a magnet comes near, even through something non-magnetic like air or paper in between. So the turning means the wire carrying current is acting on the needle like a magnet. When the current stops, the effect is gone.

The space around a magnet, or around a wire carrying current, where its magnetic effect can be felt (for example by a compass needle turning) is called a magnetic field. Think of a field as an area, like a khet, where the magnet's pull reaches.

So: when current flows through a conductor such as a wire, it makes a magnetic field around it. This is the magnetic effect of electric current. No current, no field.

You have just repeated a discovery made in 1820 by Hans Christian Oersted (1777–1851), a professor in Denmark. During a lecture he noticed that whenever he closed or opened a circuit, a nearby compass needle moved. He tested it until he was sure, then published his findings, so that other scientists could repeat the experiment and check the result.