Physics 9702 · AS & A Level · Electromagnetic induction
Electromagnetic induction — practice question
A helicopter in steady hover has four rotors, each measuring $12\,\text{m}$ in length, as shown in the top view in Fig. 7.1. At the helicopter, the vertical part of Earth’s magnetic field points downwards and has a flux density of $0.047\,\text{mT}$. Each rotor turns in the horizontal plane in the direction indicated, with a frequency of $85\,\text{Hz}$.
(a)[2]
State Lenz’s law for electromagnetic induction.
(b(i))[3]
Calculate the magnetic flux $\Phi$ cut by rotor OX in one full rotation. Include a unit in your answer.
(b(ii))[2]
Determine the magnitude of the electromotive force (e.m.f.) induced across rotor OX.
(b(iii))[2]
Use Lenz’s law to explain which end, O or X, of the rotor is at the higher potential.
Worked solution & mark scheme
This 9-mark question has a full step-by-step worked solution and mark scheme. One marking point: “direction in which the induced e.m.f. acts” …