Physics 9702 · AS & A Level · Electromagnetic induction
Electromagnetic induction — practice question
As illustrated in Fig. 5.1, the two poles of a horseshoe magnet each have dimensions $5.0\text{ cm} \times 2.4\text{ cm}$. The magnetic flux density in the space between the poles is uniform at $89\text{ mT}$. In all regions outside the poles, the magnetic flux density is zero. A rigid copper wire is attached to a sensitive ammeter with resistance $0.12\,\Omega$. The wire is then pushed by a student at a steady speed of $1.8\text{ m s}^{-1}$ through the gap between the poles, moving parallel to the pole faces.
(a)[2]
Calculate the magnetic flux between the poles of the magnet.
(b(i))[3]
Using your answer to (a), determine the e.m.f. induced in the wire as it moves between the magnet poles.
(b(ii))[1]
Show that the ammeter reading is about $70\text{ mA}$.
(c)[3]
Using Lenz’s law, a force is produced on the wire that acts against the direction of motion. The student who moved the wire through the magnetic poles says that no such force was felt. Explain quantitatively why this claim is reasonable.
Worked solution & mark scheme
This 9-mark question has a full step-by-step worked solution and mark scheme. One marking point: “$\Phi = BA = 89\times10^{-3} \times 5.0\times10^{-2} \times 2.4\times10^{-2}$” …