An a.c. source is rated at 220 V - 50 Hz. The time taken for voltage to change from its peak value to zero is

Options

A. 50 sec
B. 0.02 sec
C. 5 sec
D. `5xx10^(-3)` sec

Answer

D

Explanation

Voltage is maximum at zero time.
`therefore V=V_m cos omegat`
Now if V=0 ,
`0=V_m cos omegat`
`0=cos omegat`
`therefore omegat=pi/2`
`therefore 2pif t=pi/2`
`therefore t=1/(2xx25)`
`therefore t=1/(4xx50)`
`therefore` t=0.005
`therefore t=5xx10^(-3)` s