Question

A circular coil of radius $10cm$ is placed in a uniform magnetic field of $3.0\times 10^{-5}T$ with its plane perpendicular to the field initially. It is rotated at constant angular speed about an axis along the diameter of coil and perpendicular to magnetic field so that it undergoes half of rotation in 0.2s. The maximum value of EMF induced (in $\mu V$ ) in the coil will be close to the integer ________.

Answer 1

Answer: 15

$r=0.1m\frac{T}{2}=0.2sec$
$B=3\times 10^{-5}mT=0.4sec$
At any time flux $\varphi =BA\cos \omega t$
$|emf|=\left|\frac{d\varphi }{dt}\right|=|BA\omega \sin \omega t|$
$(emf{)}_{\max }=BA\omega =BA\frac{2\pi }{T}$
$=\frac{3\times 10^{-5}\times \pi \times (0.1{)}^2\times 2\pi }{0.4}$
$=\frac{6{\pi }^2}{4}\times 10^{-6}\left({\pi }^2\simeq 10\text{ take }\right)$
$=15\times 10^{-6}=15\mu V$