A planar loop of wire rotates in a uniform magnetic field. Initially… | JEE Main 2020 (7 Jan, Shift 2)

Q28JEE Main 2020 · 7 JAN · SHIFT 2Medium

Rotating Conductors & AC Generator

A planar loop of wire rotates in a uniform magnetic field. Initially at t = 0, the plane of the loop is perpendicular to the magnetic field. If it rotates with a period of 10 s about an axis in its plane then the magnitude of induced emf will be maximum and minimum, respectively at:

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Answer: (d)

At $t = 0$ the plane is perpendicular to $B$ : $\phi = BA\cos\omega t$ , so $e = BA\omega\sin\omega t$ .
$\omega = \frac{2\pi}{10}$ : $|e|$ is maximum when $\omega t = \frac{\pi}{2}$ , i.e. $t = 2.5\text{ s}$ .
$|e|$ is minimum (zero) when $\omega t = \pi$ , i.e. $t = 5.0\text{ s}$ .
So the answer is (d) 2.5 s and 5.0 s.

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