Determine the instantaneous value of a sinusoidal e.m.f of a frequency 50Hz and 100V maximum value, 0.001 seconds after it has passed through its zero value. Determine also the time that elapses before the voltage reaches 50 per cent of its maximum value.

Determine the instantaneous value of a sinusoidal e.m.f of a frequency 50Hz and 100V maximum value, 0.001 seconds after it has passed through its zero value. Determine also the time that elapses before the voltage reaches 50 per cent of its maximum value.