$$X_C = 1/(2\pi \times 100 \times 0.10 \times 10$$^{-6}$$)$$

Question 1

Which of the following best describes an AC circuit?

Accepted Answer

A circuit with an oscillating emf, causing the current to alternate direction.

Question 2

In an AC circuit, the voltage across and the current through a capacitor are:

Accepted Answer

90° out of phase, with current leading voltage.

Question 3

What is the mathematical relationship for the capacitive reactance $$X_C of a $$capacitor in an AC circuit?

Accepted Answer

$$X_C = \frac{1}{\omega C}$$

Question 4

A phasor is best described as:

Accepted Answer

A rotating vector representing an oscillating quantity in AC analysis.

Question 5

In a series RLC circuit, what happens at resonance?

Accepted Answer

The current is maximum.

Question 6

If the capacitance in an AC circuit is doubled, what happens to the capacitive reactance?

Accepted Answer

It is halved.

Question 7

The root-mean-square (rms) value of an AC voltage $$V_{rms} is $$related to the peak voltage $$V_0 by$$:

Accepted Answer

$$V_{rms} = \frac{V_0$}{\sqrt{2}}$$

Question 8

Which of the following is true about the current and voltage in a resistor in an AC circuit?

Accepted Answer

The current and voltage are in phase.

Question 9

In a high-pass RC filter, which frequencies are transmitted?

Accepted Answer

Frequencies $$\omega \u003e \omega_c$$

Question 10

The average power $$P_{avg}$$ dissipated in a resistor in an AC circuit is given by:

Accepted Answer

$$P_{avg} = V_{rms} I_{rms}$$

Question 11

A 0.10 $$\muF $$capacitor is connected to a 100 Hz AC source. What is the capacitive reactance $$X_C$$?

Accepted Answer

$$X_C = 1/(2\pi 	imes 100 	imes 0.10 	imes 10$$^{-6}$$)$$

Question 12

In a series RLC circuit, if the frequency is increased above resonance, what happens to the phase angle between the current and the emf?

Accepted Answer

It becomes positive, indicating current lags emf.

Question 13

Which device is used to change the voltage of AC power for transmission over long distances?

Accepted Answer

Transformer

Question 14

The instantaneous emf of an AC generator can be written as:

Accepted Answer

$$\mathcal{E}(t) = \mathcal{E}_0 \cos(\omega t)$$

Question 15

In a capacitor connected to an AC source, if the frequency is increased, what happens to the capacitive reactance $$X_C$$?

Accepted Answer

It decreases.

Question 16

Which of the following statements about energy in a capacitor in an AC circuit is correct?

Accepted Answer

Energy is stored and released, not dissipated.

Question 17

A 1600 W hair dryer is plugged into a 120 V rms outlet. What is the resistance of the heater element?

Accepted Answer

$$R = \frac{(120)^2$}{1600}$$

Question 18

In a phasor diagram for a resistor, the voltage and current phasors:

Accepted Answer

Point in the same direction.

Question 19

What is the main reason AC power is used for long-distance transmission?

Accepted Answer

Transformers can easily change AC voltage for efficient transmission.

AC Circuits and Phasor Analysis: Study Notes for Chapter 32

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