Initially a rectangular coil with length vertical is moving out with… | MHT CET 2025 (21 Apr, Shift 1)

Q12MHT CET 2025 · 21 APR · SHIFT 1Medium

Motional EMF

Initially a rectangular coil with length vertical is moving out with constant velocity ' $v$ ' in a constant magnetic field ' $B$ ' towards right. Now the same coil is rotated through $90^\circ$ in same plane in same magnetic field B and the coil is moving with same velocity $\mathbf{v}$ . The magnitude of induced e.m.f. is now

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Answer: (a)

Emf of a coil leaving the field: $\varepsilon = B\ell v$ , where $\ell$ is the side perpendicular to $\vec v$ (the vertical side here).
Initially the length $l$ (longer side) is vertical: $\varepsilon_1 = Blv$ .
After rotating by $90^\circ$ the breadth $b$ (shorter side) is vertical: $\varepsilon_2 = Bbv$ .
Since $b < l$ , $\varepsilon_2 < \varepsilon_1$ . So the working gives (b) less than the initial emf.

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