Alternating Current - Result Question 31
33. 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
[1992]
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Answer:
Correct Answer: 33. (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.
