Question-49 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 v. The magnitude of induced e.m.f. is now
(A) greater than initial induced e.m.f.
(B) less than initial induced e.m.f.
(C) equal to initial induced e.m.f.
(D) sometimes greater and sometimes less than initial induced e.m.f.
Answer : (A)
Explanation:
ψ = \vec{B} \cdot \vec{A} = BA \cos \theta
Induced emf = rate of change of flux
= -\frac{d\phi}{dt} = BA \sin \theta \frac{d\theta}{dt}
= BAω sin θ
If θ = 90°, the induced emf is maximum.
After rotating through 90°, θ = 180°.
Hence magnitude of e.m.f produced now is greater than initial induced e.m.f.