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Electromagnetic Induction: Lenz's Law

 

The direction that the induced voltage (and therefore the current) is produced in ALWAYS opposes the field that produces it (so that you have to do work to change kinetic energy into electrical energy).

This is called Lenz's Law - the induced voltage always opposes the change producing it.

Click here for an animation to illustrate this.

Here is a vidclip that illustrates Lenz's law in action.

An aluminium pipe is NOT magnetic but when a magnet is dropped through it it travels slower than it does through a glass tube, Why? Because an electric current is induced in the aluminium pipe that produces a field that opposes the field of the magnet - the repulsion therefore acts to oppose its movement and it falls slowly...