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Asked in GSEB Board July 2018 · Power factor
The power factor is cos φ, where φ is the phase angle between the source voltage and the current.
In an LR circuit the voltage across R is in phase with the current and the voltage across L leads it by 90°.
The impedance triangle has sides R and X_L at right angles and hypotenuse Z=√R²+X_L².
cos φ=R/Z=R/(√R²+X_L²).
So the power factor is R/(√R²+X_L²).
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