LuduminaMG-08 · MG-U3 · Planned
Generators, alternators and microphones
Learning objectives
Explain alternator AC and dynamo DC outputs; interpret p.d.–time graphs; explain moving-coil microphone.
8463 §§4.7.3.2–4.7.3.3 / No Trilogy counterpart
DfE single-science pp.41–42 / Combined pp.34–35. Evidence checked 30 September–1 October 2026. Skills: WS1.4,3.2,3.6; MS4a.
Explanation
An alternator produces alternating p.d.; a dynamo’s connections give unidirectional output which can still vary in magnitude. A moving-coil microphone uses induction to turn sound-driven mechanical motion into an electrical signal, the reverse conversion direction of a loudspeaker.
Concepts, equations and units: Generated p.d. V against time s; AC alternates sign, dynamo unidirectional pulsing DC; microphone pressure→motion→induction.
Prediction, demonstration and game exercise
Predict, observe, explain
Compare rotating-coil connection models and corresponding traces; reverse microphone conversion chain.
Planned learner game exercise
Select an alternator/dynamo for supplied output requirement and order microphone signal stages.
Independent practice
Draw/interpret two generator traces; write a microphone explanation contrasting loudspeaker.
Original practice example · Separate Physics Higher
A generator trace stays nonnegative but rises and falls repeatedly. Can this be DC?
Show working and model answer
Working / reasoning
DC means unidirectional; it need not be a perfectly constant value.
Answer
Yes: a pulsating unidirectional DC output is possible.
Exit check and success criteria
Correct output signs and complete microphone chain, with energy supplied by mechanical input.
During practice, compare the prediction with evidence and give an error-specific prompt. The exit item uses a fresh context or fresh values, answered independently.
Misconceptions, practical links and mastery
Check these misconceptions
Dynamo DC must be perfectly constant; microphone uses motor effect to create sound; generators create charge.
Practical preparation
Optional safe generator/microphone demonstrations; no RP.
Virtual preparation and revision only. Required hands-on activities and school records remain separate.
Proposed mastery
0: not yet evidenced. 1: supported. 2: independent exit criteria met. 3: successful changed-context transfer. Advance at 2; revisit with fresh retrieval. These are not GCSE grades.