Physics P3 - Generators and Transformers

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  • Created by: RATM33
  • Created on: 27-12-09 16:43

Generators and Transformers

Before reading this, I suggest you read The Motor Effect which is already posted up.

a.c. Generator (

· Generators rotate a coil in a magnetic field (or a magnet in a coil).

· Their construction is much like a motor. As the coil spins, a current is induced in the coil.

· This current changes every half turn.

· Instead of a split-ring commutator, AC generators have slip rings and brushes so the contacts don’t swap every half turn (as AC generators already alternate)

· This means that they produce AC voltage

· All power stations use AC generators to produce electricity; they just get the energy needed to turn the coil or magnetic field.


Dynamos are a slightly different type of generator. They rotate the magnet instead of the coil. This still causes the field through the coil to swap every half turn, so the output is just the same ads for a generator. Dynamos are sometimes used as headlights for Bikes.


Transformers change the voltage. They use electromagnetic induction, so they will only work on AC voltages. A transformer is made from two coils, one on each side of a soft iron core. They either increase or decrease the voltage. There are two types of transformer that you need to know about; Step up and Step down.

Step Up Transformers

Increase the voltage. They have more turns on the secondary coil than on the primary coil.


Step Down Transformers –

Decrease the voltage. They have more turns on the primary coil than the secondary coil.

How they work –

· The Primary coil produces a magnetic field, which stays within the iron core. This means nearly all of it passes


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