Electromagnetic induction · Year 12
When the magnetic field through a coil changes – a magnet moves in or out, or the coil turns in a field – a voltage is induced. This electromagnetic induction is how almost all the world’s electricity is generated, and how transformers, dynamos, induction hobs and contactless chargers work.
Key facts
- A voltage is induced only while the magnetic field (flux) through the circuit is changing.
- Bigger induced e.m.f.: move faster, use a stronger magnet, use more turns.
- Magnetic flux Φ = BA (Wb); flux linkage = NΦ.
- Faraday’s law: ε = NΔΦ ÷ Δt; a straight rod moving across a field: ε = BLv.
- Lenz’s law: the induced current opposes the change that causes it.
- On a flux–time graph, the induced e.m.f. is N × the gradient.