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  4. Assertion: At resonance, LCR series circuit have a minimum current. Reason: At resonance, in LCR series circuit, the current and e.m.f are not in phase with each other

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Q. Assertion : At resonance, $LCR$ series circuit have a minimum current.
Reason : At resonance, in $LCR$ series circuit, the current and e.m.f are not in phase with each other

AIIMSAIIMS 2016Alternating Current

Solution:

At resonance $X_L = X_C$ or $\omega L=\frac{1}{\omega C} .$
Because of this impedance of LCR series circuit become equal to resistance of circuit
$\left(Z=\sqrt{R^{2}+\left(X_{L}-X_{C}\right)^{2}}\right).$
Therefore from I $=\frac{E}{Z}=\frac{E}{R},$ at resonance, current in LCR series circuit is maximum. Correspondingly phase angle is also equal to zero. Therefore emf and current are in phase in LCR series circuit.