Turning a coil in a field gives a.c. through slip rings or d.c. through a commutator; reading peak, period and frequency off the output graph; and how a moving-coil microphone works.
What you will learn
- Tell an alternator from a dynamo and their output graphs apart
- Read the peak p.d. and period from a graph and work out the frequency
- Explain how a moving-coil microphone turns sound into a signal
Turning a coil in a field
Spin a coil between the poles of a magnet and the field through it keeps changing, so a p.d.
is induced. Each half turn the sides of the coil swap over, so the p.d. reverses.
- Alternator: each end of the coil connects to its own slip ring, so the reversing p.d. reaches the circuit: a.c.
- Dynamo: a split-ring commutator swaps the connections every half turn, so the output never goes below zero: d.c. that rises and falls.
One full turn of the coil gives one cycle, so the frequency in hertz is the number of turns each second (turns per minute ÷ 60).
The rest of this lesson and its 9 practice questions are locked.
In this lesson
- Turning a coil in a field
- Reading the output graph
- The moving-coil microphone
- Try it: Read the graph
9 practice questions, marked as you go; about 20 minutes in all.
Key terms
Slip ring, Split-ring commutator, Diaphragm, Coil
In this unit: Magnetism and electromagnetism
Magnets and field lines, electromagnets, the motor effect and F = BIl, then loudspeakers, generators, microphones and transformers.
- Magnets and magnetic fields
- Electromagnetism
- The motor effect
- Loudspeakers and induced potential difference
- Alternators, dynamos and microphones
- Transformers