Question

In A.C. circuit having only capacitor, the current ______.

विकल्प

• lags behind the voltage by `pi/2` in phase

• leads the voltage by `pi/2` in phase

• leads the voltage by `pi` in phase

• lags behind the voltage by `pi` in phase

Answer 1

In A.C. circuit having only capacitor, the current leads the voltage by `pi/2` in phase.

Explanation:

In pure capacitive circuit, let an A.C. voltage be supplied of the form 

e = `e_0` sin `omega`t .... (i)

we know that, C = `"q"/"e"`

`=> "q" = "Ce" = "Ce"_0` sin`omega`t

 `therefore "I" ="dq"/"dt" = "Ce"_0  omega  "cos" omegat"t"`

 `therefore "I" = "I"_0 "cos"  omega"t"`  .... `("taking"  "I"_0 = "Ce"_0 omega)`

`therefore "I" = "I"_0 sin (pi/2 + omega"t")`  .... (ii)

Thus, on comparing (i) and (ii), we see that current leads the voltage by a phase angle of `pi/2`.