Physics – 4.5.1 Electromagnetic induction | e-Consult

Here are the steps that occur when a bar magnet is moved across a stationary coil of wire:

1. Magnet far from coil: The magnetic flux linking the coil is zero. There is no induced e.m.f. or current.
2. Magnet moving towards the coil: As the magnet moves towards the coil, the magnetic flux linking the coil increases.
3. Maximum flux: When the magnet is directly in front of the coil, the magnetic flux linking the coil is at its maximum value. An e.m.f. is induced in the coil.
4. Magnet moving past the coil: As the magnet moves past the coil, the magnetic flux linking the coil decreases.
5. Magnet far from coil again: When the magnet is far from the coil again, the magnetic flux linking the coil is zero. The induced e.m.f. is zero.

The direction of the induced e.m.f. is determined by Lenz's Law. The induced e.m.f. opposes the change in magnetic flux that produced it.

• When the flux is increasing, the induced e.m.f. is in a direction that creates a magnetic field opposing the motion of the magnet.
• When the flux is decreasing, the induced e.m.f. is in a direction that creates a magnetic field opposing the decrease in flux.