In an AC generator, the number of turns in the coil is $2000$ and the area of the coil is $0.1m^2$. The coil is rotated at an angular frequency of $200$ rad/s in a magnetic field of $0.2T$. The induced emf when the plane of the coil makes an angle of 60' with the field is:

Magnetic flux when the normal to the plane of the coil makes angle $\theta$ with the field is

$\varphi =NAB\cos \theta$

Induced emf is given by

$\xi =-\frac{d\varphi }{dt}=NAB\omega \sin \theta$

When the plane of the coil makes angle $60°$with the field, the normal to the plane of the coil makes angle  $\theta =30°$ with the field. The induced emf at this instant is 

$\xi =2000\times 0.1{\mathrm{m}}^2\times 0.2\mathrm{T}\times 200\mathrm{rad}/\mathrm{s}\times$$\sin {30}^{\circ }=4000\mathrm{V}$