A square coil is situated in a horizontal uniform magnetic field. The coil’s plane is at right angles to the magnetic field. The coil is then turned about an axis passing through point $P$ at a constant rate. The coil turns through $180^{\circ}$. Which diagram shows how the electromotive force (e.m.f.) induced in the coil changes as it turns through $180^{\circ}$?
Physics 5054 · O Level · Electromagnetic induction