Q174 / 180 · COMEDK 2020 · Physics

For a series $L-C-R$ circuit at resonance, which statement is not true?

  • A
    Wattless current is zero.
  • Correct answer
    B
    Power factor is zero.
  • C
    Peak energy stored by a capacitor = peak energy stored by an inductor.
  • D
    Average power = Apparent power.

Solution

In $L-C \cdot R$ series resonance circuit, $X_{L_{L}}=X_{C}$ $\therefore$ Impedance, $Z=\sqrt{R^{2}+\left(X_{L}-X_{C}\right)^{2}}-\sqrt{R^{2}+0^{2}}$ $\Rightarrow \quad Z=R$ $\therefore$ Power factor, cos $\phi=\frac{n}{Z}=\frac{R}{R}=1$ Which is not zero. Since, circuit behaves like a resistive circuit. $\mathrm{So}$, power loss occurs always in this circuits. i.e, wattless carrent is zero.

Hence, the correct answer is option: 'B'.

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