Electromagnetic Induction - The Generator Effect

Click here to download a worksheet on this topic.

This is a very important physics discovery.

Our modern lifestyle would not be possible without electric power generation.... and electromagnetic induction is the process by which wind, wave, tidal, HEP, oil, gas, coal, nuclear and biomass energy is changed into electricity.

If a magnet is moved into a coil of wire which is part of a complete circuit a voltage is induced across the ends of the wire - a current is produced (induced) in the wire.

If the magnet is then moved out of the coil, or the other pole of the magnet is moved into the coil, the direction of the induced voltage (current) is reversed.

See here for an interactive Java application


Click on the graphic to play with an interactive demonstration.

Size of the current produced

The size of the induced voltage depends upon the 'rate of cutting of magnetic flux lines'


If the magnet is stationary with respect to the magnetic field no voltage is induced and therefore no current flows. If the wire 'cuts through' the lines of magnetic flux (crosses through field lines) a current is registered on a sensitive galvanometer (either a voltmeter or ammeter).

The faster the magnet 'cuts the magnetic flux lines' the bigger the voltage and the bigger the current flow. As if you move the magnet faster you cut through more lines of magnetic magnetic flux in a given time and you therefore get a bigger induced current and voltage.

The more turns of the wire that 'cut the magnetic flux lines' (possible if you wind the wire into a coil!) the bigger the voltage and current induced.

If you use a stronger magnet the magnetic flux lines are closer together - therefore as you move the magnet it cuts through more lines in a given time and you get a bigger induced current and voltage.

If the coil face has a bigger area the total flux intercepted by it will be bigger

The direction of the current produced

The direction of the induced current flow can be worked out using Fleming's Right Hand Rule.

Your thumb and first two fingers are held mutually at right angles as shown in the diagram.

Your thuMb represents the direction of the Movement of the wire in the magnetic field.

Your Forefinger represents the direction of the magnetic Field

Your seCond finger represents the direction of the conventional

Current flow.


See here for a page of questions to test your understanding of this.

Practical Application:

The 'shake-to-charge' flashlight

Also see:

Lenz's Law

The Electric Generator

The Microphone