3. A 800 turn coil of effective area $0.05 m^2$ is kept perpendicular to a magnetic field of $5 \times 10^{-5} T$. When the plane of the coil is rotated by $90^\circ$ around any of its coplanar axis in $0.1 s$, the emf induced in the coil will be: (2019)
Solution:
Initial flux is $\Phi_1 = N B A \cos(0^\circ) = 800 \times (5 \times 10^{-5}) \times 0.05 = 2 \times 10^{-3} Wb$.
After rotating by $90^\circ$, $\Phi_2 = N B A \cos(90^\circ) = 0$.
Magnitude of induced emf is $e = |\frac{\Delta \Phi}{\Delta t}| = \frac{2 \times 10^{-3} - 0}{0.1} = 0.02 V$.
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