# Electric generators

• An electric generator is essentially the opposite of a motor.
• A motor turns Electrical Potential Energy to Mechanical Energy.
• A generator turns ME to EPE

### Average EMF induced in a coil

Is the same as the Faraday’s law.

### Max EMF induced

EMFaverage = 2NlvB

### Instantaneous induced EMF

EMF instantaneous  = 2NlvBsinθ

Where θ = angle that the normal from the coil makes with the flux

Substitute cosθ if θ = angle the armature makes with the flux

### RMS induced EMF

That is, EMFmax divided by root 2.

### DC generator

• Very similar in design to a DC motor
• Converts mechanical energy to electrical energy
• A mechanical torque is applied to the coil, and it rotates
• This rotation cuts through flux, so induces a voltage
• The EMF produced is always positive, because of the split ring commutator

### AC generator

• Similar to DC
• Coil is fixed to two slip rings which allow the armature to rotate, resulting in an AC
• Since the coil first moves up then down, the EMF switches direction every half turn
• Results in a sine wave if you plot EMF against time