A moving-coil microphone uses the generator effect. Sound pressure variations vibrate a diaphragm and attached coil in a magnetic field. The changing field through the moving coil induces an alternating p.d.; in a complete circuit it produces a varying current representing the sound signal. Example: Describe the coil’s movement. It vibrates with the diaphragm within a magnetic field. Distinguish the observation from the explanation, and support any judgement with evidence. Link cause and effect.