Q86 / 120 · VITEEE 2012 · Physics

A resistor $\mathrm{R}$, an inductor $\mathrm{L}$ and capacitor $\mathrm{C}$ are connected in series to an oscillator of frequency n. If the resonant frequency is $n_{r}$, then the current lags behind voltage, when

  • A
    $n=0$
  • B
    $n < n_{\mathrm{r}}$
  • C
    $n=n_{\mathrm{r}}$
  • Correct answer
    D
    $n>n_{\mathrm{r}}$

Solution

When reactance of inductance is mroe than the reactance of cndenser, the current will lag behind the voltage. Thus $\omega L < \frac{1}{\omega c}$ or $\omega>\frac{1}{\sqrt{L C}}$ or $\mathrm{n}>\frac{1}{2 \pi \sqrt{\mathrm{LC}}}$ or $\mathrm{n}>\mathrm{n}_{\mathrm{r}}$ $\mathrm{n}_{\mathrm{T}}=$ resonant frequency

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

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