Paper 3 Electromagnetic Induction Drills

Q1 Flux-Time Graph

A coil has $N=120$ turns. The flux per turn changes linearly from $0$ to $5.0\times 10^{-3}\mathrm{Wb}$ in $0.20\mathrm{s}$, remains constant for $0.10\mathrm{s}$, then falls linearly to zero in $0.50\mathrm{s}$.

1. Calculate induced emf during the rising section. [2]
2. State induced emf during the constant-flux section. [1]
3. Calculate induced emf magnitude during the falling section. [2]
4. Explain why the signs of emf in rising and falling sections are opposite. [2]

Q2 Eddy Current Braking

A conducting plate moves through a magnetic field and experiences magnetic braking.

1. Explain how eddy currents are produced. [2]
2. Explain why the plate slows down. [3]
3. State one method of reducing unwanted eddy currents in a transformer core. [1]