Electromagnetic Induction

Moving a magnet towards a coil, Rotating a coil in a magnetic field, Changing the current in a nearby coil

Electromagnetic induction occurs whenever there is a change in magnetic flux. This can happen by moving a magnet relative to a coil, rotating a coil in a magnetic field, or changing the current (and thus magnetic field) in a nearby coil. Keeping both stationary with constant current produces no flux change.

ε = -dφB/dt

Faraday's law states that the induced EMF is equal to the negative rate of change of magnetic flux with time. The negative sign indicates the direction as per Lenz's law, and 'd' represents the differential (rate of change).

ε = Blv

When a conductor of length l moves with velocity v perpendicular to a magnetic field B, the motional EMF induced is ε = Blv. This can be derived from Faraday's law or from the Lorentz force on the charge carriers.

Opposition to change in current

Self-inductance (L) is a measure of a coil's opposition to changes in current flowing through it. It's the electromagnetic analogue of inertia in mechanics, resisting both increase and decrease in current.