Alternating Current Ques 27
27. An $LCR$ series circuit is connected to a source of alternating current. At resonance, the applied voltage and the current flowing through the circuit will have a phase difference of
[1994]
(a) $\pi$
(b) $\frac{\pi}{2}$
(c) $\frac{\pi}{4}$
(d) $0$
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Answer:
Correct Answer: 27.(d)
Solution:
- (d) At resonance, $\omega L=\frac{1}{\omega C}$. The circuit behaves as if it contains $R$ only. So, phase difference $=0$
At resonance, impedance is minimum $Z _{\text{min }}=R$ and current is maximum, given by
$ I _{\max }=\frac{E}{Z _{\min }}=\frac{E}{R} $
It is interesting to note that before resonance the current leads the applied emf, at resonance it is in phase, and after resonance it lags behind the emf. $LCR$ series circuit is also called as acceptor circuit and parallel $LCR$ circuit is called rejector circuit.
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