A coil of mean area 500   cm 2 and having 1000 turns is held with its plane perpendicular to a uniform…

At time, $\mathrm{\Delta }t=\frac{1}{10}=0.1 \mathrm{s}$

Coil turned from $\theta =0$ to $180°$

The expression for the change in flux is,

$\mathrm{\Delta }\theta ={\theta }_f-\theta$

$\mathrm{\Delta }\theta =NBA\cos 180°-NBA\cos 0°$

$\mathrm{\Delta }\theta =-2NBA$

The emf induced is,

$E=-\frac{\mathrm{\Delta }\theta }{\mathrm{\Delta }t}$

$E=-\left(\frac{-2NBA}{\mathrm{\Delta }t}\right)$

$E=\frac{2NBA}{\mathrm{\Delta }t}$

Substitute the values in the above equation.
$E=\frac{2\times 1000\times 0.4\times {10}^{-4}\times 0.05}{0.1}$

$=0.04 \mathrm{V}$