The generator effect, what changes the size and direction of the induced potential difference, alternators and dynamos, and how microphones and loudspeakers work. Physics only content.
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1.What is the generator effect?
When a conductor moves relative to a magnetic field, a potential difference is induced across the conductor.
2.When does an induced current flow?
When the conductor is part of a complete circuit.
3.Give two ways of inducing a potential difference.
Moving a conductor through a magnetic field, or moving a magnet into or out of a coil.
4.What happens if the conductor is stationary in a steady field?
No potential difference is induced, because there is no change.
5.Give three ways to increase the size of the induced potential difference.
Move the magnet or conductor faster, use a stronger magnet, and use more turns on the coil.
6.What happens to the induced potential difference if the direction of motion is reversed?
It is induced in the opposite direction.
7.What happens if the poles of the magnet are swapped?
The induced potential difference is also reversed.
8.What does the induced current do to the original magnetic field?
It produces a magnetic field that opposes the original change.
9.Why does the induced field oppose the change?
If it reinforced the change, energy would be created from nothing, which would break conservation of energy.
10.What is an alternator?
A generator that produces alternating current.
11.What does an alternator use to connect to the circuit?
Slip rings and brushes.
12.Why do slip rings produce alternating current?
Each side of the coil stays connected to the same contact, so the current reverses as the coil turns.
13.What is a dynamo?
A generator that produces direct current.
14.What does a dynamo use to connect to the circuit?
A split ring commutator.
15.Why does a split ring produce direct current?
It swaps the connections every half turn, so the current in the external circuit always flows the same way.
16.Describe the output of an alternator on an oscilloscope.
A wave that alternates above and below zero.
17.Describe the output of a dynamo on an oscilloscope.
A series of pulses all on the same side of zero, never going negative.
18.How does a microphone work?
Sound waves make a diaphragm vibrate, which moves a coil in a magnetic field, inducing a current that varies with the sound.
19.What is the energy transfer in a microphone?
From the kinetic store of the vibrating diaphragm to an electrical output.
20.How is a microphone the reverse of a loudspeaker?
A loudspeaker turns a varying current into movement and sound. A microphone turns sound and movement into a varying current.
21.Why does a bicycle dynamo light dim when you slow down?
A slower rotation means a smaller rate of change, so a smaller potential difference is induced.
22.What must change for a potential difference to be induced in a coil?
The magnetic field through the coil must be changing.
23.Why does holding a magnet still inside a coil induce nothing?
The field through the coil is constant, so there is no change to induce a potential difference.
24.What energy transfer happens in a generator?
Energy is transferred mechanically from whatever turns the coil, and electrically to the circuit.
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