Capacitors in AC Circuits

Which statement describes the waveforms in this circuit for the current to lead the voltage?

• When the voltage waveform is crossing zero, the current is at zero.

• When the voltage waveform is crossing zero, the current is at a peak.

• When the voltage waveform is crossing zero, the current is changing most rapidly.

• When the voltage waveform is crossing zero, the current is constant.

What is the capacitive reactance of this circuit? Give your answer in Ω to 1 d.p.

• 10.5 Ω

• 15.2 Ω

• 20.3 Ω

• 25.4 Ω

What is the capacitive reactance (Xc) in the given circuit with a 33 µF capacitor connected to a 70 V, 50 Hz AC supply?

• 10 Ω

• 20 Ω

• 30 Ω

• 40 Ω

What effect does capacitive reactance have on the AC voltage and current applied to it?

• The capacitive reactance has no effect.

• The capacitive reactance increases the supply voltage.

• The capacitive reactance increases the supply current.

• The capacitive reactance opposes the changing supply voltage.

What will happen in this circuit if the 47 µF capacitor is replaced by a 5 Ω resistor?

• The circuit will short circuit.

• The circuit will open circuit.

• The circuit will function normally.

• The circuit will have increased resistance.

Consider the circuit diagram with a 20 V, 675 Hz AC source and a 47 μF capacitor. What will happen to the values of voltage, current, or their phase relationship?

• There will be no change to the values of voltage, or current, or their phase relationship.

• The current will be approximately the same and will be in phase with the supply voltage.

• The current will be approximately the same and will be leading the supply voltage.

• The voltage will double and the current will halve but their phase relationship will be unchanged.