Question

An electric bulb and a capacitor, are connected in series with an AC source. On increasing the frequency of the source, the brightness of the bulb will:

• A. Increase
• B. Decrease
• C. Remain unchanged
• D. increase or decrease, depending upon the resistance of the bulb

Answer 1

The correct option is A Increase

In an RC circuit, the brightness of the bulb depends upon the power delivered to it, so,

$\Rightarrow P_{out}=\left(\frac{E_{rms}}{Z}\right)R$

Here, $Z=\sqrt{R^2+{\left(\frac{1}{\omega C}\right)}^2}$

As $\omega$ is increased, $Z$ decreases, so that, $P_{out}$ increases. So, the brightness of the bulb will increase.

Hence, $\left(A\right)$ is the correct answer.