Question

A sinusoidal voltage of peak value 283 V and frequency 50 Hz is applied to a series LCR circuit in which `R = 3 ohm`, `L = 25.48 mH` and `C = 796 mu F`. Find (a) the impedance of the circuit (b) phase difference between the voltage across the source and current (c) the power dissipated in the circuit and (d) the power factor.

Answer 1

(a) To find the impedance of the circuit, we first calculate `x_(L)` and `X_(C)`.
`x_(L)=2pivL`
`=2xx3.14xx50xx25.48xx10^(-3)Omega=8Omega`
`x_(c)=(1)/(2pivC)`
`=(1)/(2xx3.14xx50xx796xx10^(-6))=4Omega`
Therefore,
`Z=sqrt(R^(2)+(X_(L)-X_(C))^(2))=sqrt(3^(2)+(8-4)^(2))`
(b) Phase difference, `phi=tan^(-1)(X_(C)-X_(L))/(R)`
`=tan^(-1)((4-8)/(3))=-53.1^(@)`
Sinc `phi` is negative, the current in the circuit lags the across the source.
(c) The power dissipated in the circuit is
`P=I^(2)R`
Now, `l=(t_(m))/sqrt(2)=(1)/sqrt(2)((283)/(5))=40A`
Therefore, `P=(40A)^(2)xx3Omega=4800W`
(d) Power factor `=cosphi=cos(-53.1^(@))=0.6`