The peak value of an alternating emf $e$ given by $e = e_0 \cos \omega t$ is $10\text{ V}$ and its frequency is $50\text{ Hz}$. At time $t = \frac{1}{600}\text{ s}$, the instantaneous e.m.f is $\left[\cos \frac{\pi}{6} = \sin \frac{\pi}{3} = \frac{\sqrt{3}}{2}\right]$