Forces and Interactions
Magnetic and heating effects of current
Explain how a current makes a magnet and how it makes heat, and say what changes the strength of an electromagnet.
At the school exhibition, Sumana's model had no magnet in it — just an iron nail wrapped in wire and connected to a battery. She closed the circuit and the nail picked up a heap of paper clips. She opened it and they dropped off. Mohini and Aakarsh had learned that iron is attracted by a magnet; here was iron behaving like the magnet.
Two effects of one current
When electric current flows through a conductor it produces a magnetic field around it — the magnetic effect of electric current — and that field disappears when the current stops. The same current also meets resistance in the conductor, and the resistance turns some electrical energy into heat: the heating effect of electric current.
Worked example
A compass is placed beneath a straight wire in a circuit, and the switch is flicked on and off a few times. What does the needle do, and what does it prove?
With the switch on, the needle swings away from the direction it was resting in.
A compass needle is itself a small magnet, so anything that deflects it must be magnetic.
Try it together
A coil of insulated wire is wound on a paper cylinder and connected to a cell. Compasses sit at each end.
A short answer is enough each time.
1.An iron nail is pushed into the middle of the coil. Does the compass deflection get bigger or smaller?
Have a go
Have a go on your own. A current carrying coil that behaves as a magnet has a one-word name. What is it?
Ready to practice?
Eight questions on what you have just read. Nothing is timed, and you can play as many times as you like.