AQA GCSE Physics (8463), Higher tier · Magnetism and electromagnetism › Induced potential and transformers
Practise Microphones. 12 exam-style questions on this subtopic, at up to four difficulty levels, with full mark schemes and a progress tracker. Free, no account needed.
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Name the part of the microphone that vibrates when sound waves reach it.
The diaphragm
State what is attached to the diaphragm of a moving-coil microphone.
A coil of wire.
State why a moving-coil microphone contains a permanent magnet.
It produces the magnetic field that the coil moves through.
Sample questions
Written for this site in the style of AQA exam questions. They are not taken from real past papers.
Question 1Easy4 marks
A moving-coil microphone contains a thin diaphragm attached to a coil of wire. The coil is in the magnetic field of a permanent magnet.
(a) What does a microphone do? Tick (✓) one box.[1]
It converts pressure variations in sound waves into variations in current.
It converts variations in current into pressure variations in sound waves.
It converts light into electrical energy.
It makes sounds louder without using electricity.
(b) Which effect does a moving-coil microphone use? Tick (✓) one box.[1]
The generator effect
The motor effect
(c) Name the part of the microphone that vibrates when sound waves reach it.[1]
(d) The microphone is connected to an oscilloscope. The sound becomes louder but its pitch does not change. What happens to the trace on the oscilloscope?[1]
Show the answer and mark scheme
(a)Answer: It converts pressure variations in sound waves into variations in current.
(b)Answer: The generator effect
(c)Answer: The diaphragm
the diaphragm
(d)Answer: The waves on the trace become taller.
the amplitude / height of the trace increases (the frequency stays the same)
Question 2Medium6 marks
A moving-coil microphone contains a diaphragm attached to a coil. The coil is in the magnetic field of a permanent magnet.
(a) Explain how the microphone produces an alternating current when sound waves reach it.[4]
(b) A microphone and a loudspeaker contain similar parts. Describe how the way a microphone works is different from the way a loudspeaker works.[2]
Show the answer and mark scheme
(a)Answer: The sound makes the diaphragm and coil vibrate in the magnetic field, inducing a pd that reverses as the coil changes direction, so an alternating current flows.
the pressure variations of the sound wave make the diaphragm vibrate
the coil (attached to the diaphragm) moves backwards and forwards in the magnetic field
a potential difference is induced across the coil (generator effect), causing a current in the circuit
the induced pd reverses each time the coil changes direction, so the current alternates (at the frequency of the sound)
(b)Answer: A microphone: movement induces a current (generator effect). A loudspeaker: current causes movement (motor effect).
in a microphone, movement of the coil induces a current (generator effect)
in a loudspeaker, a current in the coil causes a force that moves the coil (motor effect)
Question 3Hard3 marks
A sound engineer is recording a very quiet whisper for one part of a film, and a very loud explosion sound effect for another part, using the same type of moving-coil microphone.
Evaluate what the engineer should consider about the microphone's placement and settings for each recording.[3]
Show the answer and mark scheme
Answer: Place the microphone close for the quiet whisper (to get a detectable signal) but further away for the loud explosion (to avoid an excessive, possibly damaging, diaphragm movement), adjusting the recording gain for each.
for the quiet whisper, the microphone should be placed close to the source, since a quiet sound produces only a small diaphragm movement and a small induced potential difference, which is easier to detect clearly close up
for the loud explosion, the microphone can (or should) be placed further away, because a loud sound would move the diaphragm with a large amplitude, and too large a movement close up could distort the signal or even damage the microphone
the recording equipment's amplification (gain) may also need to be increased for the whisper and decreased for the explosion, to keep both signals within a useable range