Question

A resistor R, inductor L and a capacitor C are connected in series to an oscillator of frequency v. If the resonant frequency is $v_r$, then the current lags behind the voltage, when:

• A. $v=0$
• B. $v<v_r$
• C. $v>v_r$
• D. $v=v_r$

Answer 1

Answer: (C)

$v>v_r$

The current will lag behind the voltage when reactance of inductor is more than the reactance of capacitor i.e.,
$\omega L>\frac{1}{\omega c}$
or $\omega >\frac{1}{\sqrt{LC}}or2\pi v>\frac{1}{\sqrt{LC}}$
$v>\frac{1}{2\pi \sqrt{LC}}orv>v_r$
where $v_r$ is the resonant frequency.