Question 15

A coil is placed perpendicular to a magnetic field of $$5000$$ T. When the field is changed to $$3000$$ T in $$2$$ s, an induced emf of $$22$$ V is produced in the coil. If the diameter of the coil is $$0.02$$ m, then the number of turns in the coil is:

$$|emf| = N\frac{d\Phi}{dt} = N \cdot A \cdot \frac{\Delta B}{\Delta t}$$.

$$A = \pi(0.01)^2 = \pi \times 10^{-4}$$. $$\Delta B = 5000-3000 = 2000$$ T. $$\Delta t = 2$$ s.

$$22 = N \times \pi \times 10^{-4} \times 1000 = N \times 0.1\pi$$.

$$N = \frac{22}{0.1\pi} = \frac{220}{\pi} \approx 70$$.

The answer is Option (2): 70.

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