1.

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

Answer»

50 sec
0.02 sec
5 sec
`5xx10^(-3)` sec

Solution :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


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