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An AC source of fixed amplitude V0 and variable angular frequency omega is connected in series with a capacitor C and a bulb of resistance R (no inductance). As omega is increased, what happens?

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

Correct answer: The bulb glows brighter

Solution

The series impedance is Z = sqrt(R² + (1/(omega*C))²). Increasing omega reduces the capacitive reactance 1/(omega*C), so Z decreases, the current increases, and the power dissipated in the bulb (I²*R) rises - the bulb glows brighter.

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