Flux and Faraday's law, Lenz's law argued from energy rather than memorised, motional emf, the AC generator and transformer, eddy currents, and self and mutual inductance with ½LI².
Unit 4 carries 9 of the 50 physics marks; with seven chapters sharing them, this one averages a little over one (MEC publishes weights by unit, not by chapter). It is worth more attention than that average suggests, because it feeds directly into Alternating currents — the generator, the transformer and the inductor all start here — and because its questions are mostly reasoning rather than arithmetic.
The MEC scope lines are: Faraday's and Lenz's laws; AC generator, transformer and eddy currents; Self and mutual inductance; energy stored in an inductor. The headings below are those points, in MEC's order.
Three ways it is asked: recall (the unit of inductance, the transformer turns-ratio equation, what laminating a core is for); understanding (why Lenz's law must hold if energy is conserved, why a transformer will not work on direct current, why a magnet falls slowly down a copper pipe); application (an emf from a stated rate of change of flux, Blv for a rod on rails, a turns ratio, ½LI²).
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