In a series L-R circuit, XL = R and power factor of the circuit is P1. When a capacitor with capacitance C such that XL = XC is put in series, the power factor becomes P2. Find P1/ P2 .

In a LC-R Circuit, Impedence , Z = ( R2 + (XL- Xc)2)1/2 and Power Factor , P = R/Z

Case 1:-When XL = R, Z = (2R2)1/2  = (2)1/2R and so P1= R/ (2)1/2R => P1= 1/ (2)1/2

Case 2 :- WHen XL = XC, Z = R AND SO   Power Factor P2 = R/R = 1

So Ratio is P1 : P2 = 1/(2)1/2 : 1

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