Question

A capacitor, an inductor and an electric bulb are connected in series to an AC supply of variable frequency. As the frequency of the supply is increased gradually from zero, then the brightness of the electric bulb is found to

• A. increase
• B. decrease
• C. increase, reach a maximum and then decrease
• D. show no change

Answer 1

The correct option is C increase, reach a maximum and then decrease

For 0 < $\omega$ < ${\omega }_0$ impedance decreases and current increases, where ${\omega }_0$ is resonant frequency.
At $\omega ={\omega }_0$ impedance is minimum and current is maximum.
For $\omega$ > ${\omega }_0$ impedance increases and current decreases.