An alternating current of frequency 'f ' is flowing in a circuit containing a resistance R and a choke L in series. The impedance of this circuit is
R+ 2πfL
R2+4π2f2L2
R2+L2
R2+2πfL
Z=R2+XL2, XL=ωL and ω=2πf
∴Z=R2+4π2f2L2