The generator effect

​​In a nutshell

Electromagnetic induction is the production of electricity when a wire moves relative to a magnetic field or experiences a changing magnetic field. This is the generator effect. Microphones use the generator effect to transfer sound waves into electrical signals.

The generator effect (electromagnetic induction)

The generator effect is caused by electromagnetic induction. Electromagnetic induction is the production of a potential difference when a conductor experiences a change in magnetic field. This can be used to create a current if the wire is part of a complete circuit.

There are two ways the generator effect can be shown. The first is by moving a magnet inside a coil of wire. The second is by moving a conductor in a magnetic field. Both methods produce a current in the wire.

	1. Coil of wire 2. Magnet 3. Movement of magnet inside coil
	1. Conductor (long, straight wire) 2. Movement of conductor

Moving the magnet back and forth creates an alternating current, as the potential difference produced keeps swapping directions. Rotating the magnet end-to-end also produces an alternating current. This is because the magnetic field in the coil changes. From this a potential difference is produced. The direction of the magnetic field reverses after the magnet completes a half turn.

The current produced is known as the induced current. 

To increase the size of the induced current:

• The conductor or magnet can be moved faster.
  
• Stronger magnets can be used.
• More turns of wire can be used

Generators

A generator uses a turning force on a coil in a magnetic field to produce an alternating current.

1. Slip rings 2. Brushes 3. Direction the loop of wire spins 4. Direction of the current produced in the wire 5. Alternating potential difference produced

A generator is similar to a motor but doesn't use a split-ring commutator. Instead it uses slip rings to allow the coil to spin, and brushes to create a completed circuit. As the direction of the force is not switched each half turn, an alternating current is produced.

Microphones

A microphone uses the generator effect to transfer sound waves into electrical signals. The generator effect occurs when a coil of wire moves in a magnetic field which generates a current. 

1. Permanent magnet (south pole) 2. Coil wrapped around iron core (north pole) 3. Potential difference produced 4. Diaphragm  5. Sound waves vibrating diaphragm

Sound waves are made up of high pressure areas (compressions) and low pressure areas (rarefactions). A sound wave's compressions cause the diaphragm to move inwards. The sound wave's rarefaction cause the diaphragm to move outwards. 

The movement of the diaphragm causes the coil of wire attached to also move. This produces the generator effect, which generates an alternating current through the coil. 

The variations in pressure of the sound wave causes the coil to move back at forth at different speeds and different distances. This induces different potential differences and therefore produces different signals. 

The frequency of the signal depends on the pitch of the sound. The amplitude of the signal depends on the volume of the sound.