Question

The power of factor L-R circuit is objective answer

Answer 1

The variation of impedance (Z) in any RL circuit is shown below. The inductive reactance (XL) may vary either through a change in L or change in frequency as XL=2πfL=ωL

From the diagram θ=atan(XLR) so power factor is Cos(θ) or

PF=Cos(θ)=Cos(atan(XLR))=Cos(atan(2πfLR))