JEE Main · 2023 · 06 Apr 2023 · Shift 1 · Electromagnetic Induction

An emf is induced only when the magnetic flux $\varphi =BA\cos \theta$ linking the coil changes with time. Moving a coil with uniform or non-uniform speed entirely within a uniform field leaves $B$, $A$ and $\theta$ unchanged, so the flux is constant and no emf appears. Rotating the coil in the field continuously changes the angle $\theta$, so the flux varies and an emf is induced. Changing the area of the coil in the field directly changes the flux and also induces an emf. The induced emf is therefore produced by rotating the coil and by changing its area.