Generators · Grade 9
In Grade 9 you learn: generators: kinetic to electrical energy; the generator effect: induced voltage; turns each second from turns a minute.
Moving a wire across a magnetic field, or changing the field through a coil, induces a voltage: the generator effect. A generator spins a coil in a magnetic field, so kinetic energy becomes electrical energy. An alternator gives alternating current through slip rings; a dynamo gives direct current through a commutator. Spinning faster gives a bigger, more frequent output.
Key facts
- The generator effect: moving a wire or coil through a magnetic field, or moving a magnet in a coil, induces a voltage.
- Motor: electrical → kinetic energy. Generator: kinetic → electrical energy.
Worked examples
Example 1
What energy transfer happens in a generator?
Answer: kinetic → electrical
Example 2
A magnet is pushed into a coil joined to a sensitive ammeter, and the needle flicks to the right. What happens when the magnet is pulled out again?
Answer: The needle flicks to the left: the induced current reverses.
Example 3
How can you make a generator give a bigger voltage?
Answer: Spin it faster, use more turns on the coil, or use a stronger magnet.
Example 4
In a moving-coil microphone, what happens when sound hits the diaphragm?
Answer: The coil moves in a magnetic field and a voltage is induced