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electromagnetic induction
The phenomenon in which an electric field is generated in an electric circuit when the number of magnetic field lines passing through the circuit changes. Electromagnetic induction was discovered independently by Michael Faraday and Joseph Henry. The voltage induced is proportional to the rate of change of the field, and large voltages can be produced by switching off quite small magnetic fields suddenly. Frequently, the magnetic field is itself generated by an electric current in a coil, in which case the voltage induced is proportional to the rate of change of the current (see inductance).
The principle finds numerous applications in electric generators and motors, transformers, microphones, and engine ignition systems. In the less familiar technique of induction heating, widely used in metal working, an object is heated by currents created in it by the voltage induced by a high-frequency current in a nearby coil; as the coil field will pass through insulators without heating them, the principle can be applied to produce "cold hob" electric stoves.
Related category
• ELECTRICITY AND MAGNETISM
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