Explanation

(a) Since, current lags behind the voltage in phase by a constant angle, then circuit must contain R and L.
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We find that in R – L circuit, voltage leads the current by a phase angle $\phi$, where
$\tan{\phi = \frac{AK}{OA}} = \frac{OL}{OA}$
$= \frac{V_{L}}{V_{R}} = \frac{I_{0}X_{L}}{I_{0}R}$
$\therefore\ \ \ \ \ \ \ \ \ \ \ \ \ \ \tan{\phi = \frac{X_{L}}{R}}$
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