Question

A wheel having metal spokes of 1 m long between its axle and rim is rotating in a magnetic field of flux density $5\times {10}^{-5}$ T normal to the plane of the wheel. An e.m.f of $\frac{22}{7}mV$ is produced between the rim and the axle of the wheel. The rate of rotation of the wheel in revolutions per seconds is

• A. 10
• B. 20
• C. 30
• D. 40

Answer 1

The correct option is B 20

$e=\frac{1}{2}B{l}^{2}w$
$\pi \times {10}^{-3}=\frac{1}{2}\times 5\times {10}^{-5}\times 1\times 2\pi f$
The frequency of rotation is
$f=\frac{100}{5}=20$