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# Power factor of resonance LCR circuit is

$(a)\;1 \\(b)\;0.1 \\ (c)\;\frac{1}{4} \\ (d)\;\frac{2}{6}$

$\cos \phi$ is the power factor
$\cos \phi =\large\frac{R}{\sqrt {[R^2+(Lw -\Large\frac{1}{cw})^2]}}$
at resonance $Lw=\large\frac{1}{cw}$
$\cos \phi=1$
Hence a is the correct answer.