The generator effect

How is electricity generated?

moving a wire up and down a magnetic field to cause an induced potential difference and current to flow

What is the generator effect?

The induction of a potential difference in a wire that is experiencing a changing magnetic field

How to induce potential difference in a bar magnet?

move it into and out of a coil of wire to create a changing magnetic field

Faraday’s Law

the size of the induced potential difference is proportional to the rate of change of magnetic flux

If you move the magnet faster

the rate of change of magnetic flux will be greater

so the induced potential difference will be greater

Lenz’s Law

the direction of the induced potential difference is such that it opposes the change that is made

When the magnet is moved into the coil of wire

the end of the wire becomes the same pole as the magnet

so it repels the magnet and current is reversed

as the magnet moves away, the end becomes opposite to the pole of the magnet

and attracts it

How can you increase the induced potential difference?

1. Use stronger magnets

2. Increase number of coils on the wire

3. Increase the speed at which you move the magnet

How can you reverse the direction of the potential difference?

1. Reverse the way you move the magnet

2. Reverse the polarity of the magnet

how does the alternator work?

1. As the coil rotates, it move through the magnetic field

2. A potential difference is induced across the coil

3. As there is a complete circuit, a current is induced.

4. Since the coil rotates, the current changes direction every half-turn

5. The slip-rings and brushes ensure that the contact do not swap every half turn

6. An altenating current is produced

Explain this graph

• the pd is greatest when the plane of the coil is parallel to the direction of the magnetic field

• the pd is 0 when the plane of the coil is perpendicular to the direction of the magnetic field since no coils cut through the field

• the pd alternates between the positive and negative terminals as the direction is reversed

How does a Dynamo work?

1. As the coil rotates, it moves through the magnetic field

2. A potential difference is induced across the coil

3. Since there is a complete circuit, a current is induced

4. The single split ring commutator allows the two ends of the coil to swap as each half-revolution from one brush to the other

5. This means that the direction of the induced potential difference does not reverse every half turn

6. Meaning that a direct current flows

Explain this graph

• the pd is greatest when the plane of the coil is parallel to the direction of the magnetic field

• the pd is 0 when the plane of the coil is perpendicular to the direction of the magnetic field since no coils cut through the field

• Since pd only flows in one direction, the pd is always positive

What happens when you increase the frequency of revolutions?

• the amplitude will increase

  since the rate of change of magnetic flux increases

• the frequency will increase, the wavelength will decrease and there will be more peaks

  since the coil makes revolution in half the times

How does a moving coil microphone work?

1. sound waves cause the diaphragm to vibrate

2. the diaphragm causes the coil to vibrate

3. the coil wire moves through the magnetic field of the permanent magnet

4. a potential difference is induced across the ends of the coil