A coil has `1,000` turns and `500 cm^(2)` as its area. The plane of the coil is placed at right angles to a magnetic induction field of `2 xx 10^(-5) web//m^(2)`. The coil is rotated through `180^(@)` in `0.2` second. The average emf induced in the coil, in milli volts, is :

Options

A. 5
B. 10
C. 15
D. 20

Answer

B

Explanation

When the plane of a coil is perpendicular to the field the flux linked with the coil is
`phi_1 = NBA cos 0^@ = NBA`
When the coil is turned through `180^@` , the flux linked with the coil is
`phi_2 = NBA cos 180^@ = -NBA" " (because cos 180^@ = -1)`
`therefore ` Change in flux , `Delta phi = phi_2 - phi_1`
`|Delta phi| = 2NBA`
Magnitude of average emf induced is
`|epsi_(av)| = (|Delta phi|)/(Delta t) = (2NBA)/(Delta t ) = (2 xx 1000 xx 2 xx 10^(-5) xx 500 xx 10^(-4))/(0.2)`
`= 10 xx 10^(-3) V = 10mV`