A moving-coil microphone is connected to an oscilloscope. A sound makes the diaphragm vibrate. The diaphragm is then clamped so that the coil cannot move, while the sound continues unchanged.
What happens to the signal after any brief disturbance?
It remains unchanged because sound still reaches the permanent magnet.
Its frequency doubles because the stationary coil cuts more field lines.
Its amplitude increases because the clamped coil has greater resistance.
It becomes zero because the coil no longer moves through the field.
92 exam-style questions on Edexcel GCSE Physics 13.1 Inducing a current, covering 13.1.1 Producing an electric current by induction, 13.1.2 Factors affecting the induced potential difference, 13.1.3 Alternators and dynamos, and 13.1.4 Microphones and loudspeakers. Each one has a worked solution and a mark scheme showing where the marks go.