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An AC voltage source of variable angular frequency \(\omega\) and fixed amplitude \(V\) is connected in series with a capacitance \(C\) and an electric bulb of resistance \(R\) (inductance zero). When \(\omega\) is increased:

1. the bulb glows dimmer
2. the bulb glows brighter
3. total impedance of the circuit is unchanged
4. total impedance of the circuit increases

Correct answer: the bulb glows brighter

Solution

As angular frequency increases, capacitive reactance \(X_C=1/(\omega C)\) decreases. Therefore the total impedance of the series circuit decreases, current increases, and the bulb glows brighter.

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