The impedance of the network in the figure below is found to

The impedance of the network in the figure below is found to be purely real at f = 400 Hz. What is the value of C? mF

Solution

Impedance Z is completely real : Admittance is completely real

Admittance = 1/(R+jwL) +jwC

Img(Admittance) = wC-wL/(R^2+(wL)^2) = 0

=> C(R^2+(wL)^2) = L

=> C = L/(R^2+(wL)^2) = 15.6uF