Question

A disc of radius $0.1\ m$ is rotating with a frequency $10\, rev / s$ in a normal magnetic field of strength $0.1\, T$. Net induced emf is

• A. $ 2\pi \times 10^{-2}V $
• B. $ 2\pi^2 \times 10^{-2}V $
• C. $ \frac{\pi }{2}\times 10^{-2}V $
• D. None of these

Answer 1

Answer: (B)

Given : $r =0.1 m \quad v=10 rev / s \quad B =0.1 T$
Area of disc $A =\pi r ^{2}=\pi(0.1)^{2} m ^{2}$
Angular frequency $\quad W =2 \pi v=20 \pi rad / s$
$\therefore$ Emf induced $\quad E = BAw =0.1 \times \pi(0.1)^{2} \times 20 \pi=2 \pi^{2} \times 10^{-2} V$