Paper 4 Electromagnetic Induction Answers

Q1 Magnet and Coil Investigation

1. Induced emf/p.d. across the coil as a function of time. [1]
2. Flux linkage changes in one direction as the magnet enters and in the opposite direction as it leaves, so induced emf reverses. [2]
3. Use more turns, stronger magnet, faster motion, larger coil area where appropriate, or soft iron core. [2]

Q2 Sliding Rod Practical Model

1. Axes correctly oriented and labelled [1]; sensible scales [1]; all six points plotted accurately [2]; best-fit straight line [1].

2. The gradient is approximately $0.125\mathrm{V}\mathrm{s}{\mathrm{m}}^{-1}$. Accept a value consistent with the candidate’s graph. [2]

3. Since the gradient is $Bl$,

   $$B=\frac{0.125}{0.250}=0.500\mathrm{T}.$$

   [2]

4. The points lie close to a straight line whose intercept is consistent with zero, so they support direct proportionality within experimental scatter. [2]

5. Measure speed with light gates, video analysis or a motion sensor [1]. Keep $B$, active length and orientation fixed; ensure the rod, its velocity and the field are mutually perpendicular; or keep stationary circuit branches outside the field [1].