Deck 24: Alternating-Current Circuits

Question 1

The inductive reactance of an inductor is higher at low frequencies.

Answer 1

False

Question 2

In a series RLC circuit an inductor will be dominant at higher frequencies.

Answer 2

True

Question 3

A resistor and a capacitor are connected in series to an ideal battery of constant terminal voltage. At the moment contact is made with the battery, the voltage across the capacitor is

A) greater than the battery's terminal voltage.
B) equal to the battery's terminal voltage.
C) less than the battery's terminal voltage, but greater than zero.
D) zero.

Answer 3

zero.

Question 4

A pure capacitor is connected to an AC power supply. In this circuit, the current

A) leads the voltage by 90°.
B) lags the voltage by 90°.
C) lags the voltage by 180°.
D) is in phase with the voltage.
E) none of the given answers

Question 5

FIGURE 24-1
Figure 24-1 shows a simple ac circuit composed of a capacitor connected across the terminals of an ac generator. If the frequency of the generator is doubled, what happens to the capacitive reactance of the capacitor?

A) It increases by a factor of 4.
B) It increases by a factor of 2.
C) It increases by a factor of .
D) It decreases by a factor of 2.
E) It decreases by a factor of 4.

Question 6

Which one of the following is the correct expression for the sinusoidal ac voltage?

A) V = V_max sin ωt
B) V = I_max sin ωt
C) V = (V_max /R)sin ωt
D) All of the above answers are correct.
E) None of the above answers is correct.

Question 7

The capacitive reactance of a capacitor is very small at low frequencies.

Question 8

Consider a capacitor connected across the AC supply. The current through the capacitor will ________ as the capacitance is increased.

A) increase
B) remain constant
C) decrease

Question 9

An electric circuit consists of a resistor connected across the terminals of an ac generator. How does the power dissipated in the resistor change as the frequency in the generator decreases?

A) It decreases.
B) It increases.
C) It does not change.
D) It increases or decreases depending on the sign of the phase angle.

Question 10

In a series RLC circuit a capacitor will be dominant at lower frequencies.

Question 11

The capacitive reactance increases with the capacitance.

Question 12

Which of the following is the correct expression for the SI units of the capacitive reactance?

A) Ω∙S
B) Ω/S
C) J∙A/s
D) Ω
E) J/m

Question 13

A resistor is connected to an AC power supply. On this circuit, the current

A) leads the voltage by 90°.
B) lags the voltage by 90°.
C) is in phase with the voltage.
D) leads the voltage by 45°.
E) lags the voltage by 45°.

Question 14

A resistor and a capacitor are connected in series to an ideal battery of constant terminal voltage. At the moment contact is made with the battery, the voltage across the resistor is

A) greater than the battery's terminal voltage.
B) equal to the battery's terminal voltage.
C) less than the battery's terminal voltage, but greater than zero.
D) zero.

Question 15

An ac signal of a certain frequency is applied to a capacitor. The current leads the voltage by 90°.

Question 16

A series RLC circuit connected across an ac voltage source has minimum current flowing through the circuit when operating at the resonant frequency.

Question 17

If you triple the rms voltage in an ac circuit, what happens to the maximum voltage?

A) It increases by a factor of .
B) It decreases by a factor of .
C) It decreases by a factor of 3.
D) It increases by a factor of 3.
E) It increases by a factor of 9.

Question 18

In a pure resistive circuit, the phase angle between current and voltage is

A) 0.
B) π/2 radians.
C) -π/2 radians.
D) π radians.
E) 3π/4 radians.

Question 19

A series RLC circuit connected across an ac voltage source will have a positive value of the phase angle at high frequencies.

Question 20

The capacitive reactance is directly proportional to the frequency of the applied ac signal.

Question 21

Resonance in a series RLC circuit occurs when

A) X_L is greater than X_C.
B) X_C is greater than X_L.
C) (X_L - X_C) is equal to R².
D) (X_L - X_C)² is equal to R².
E) X_C equals X_L.

Question 22

Consider an RLC circuit that is driven by an AC applied voltage. At resonance,

A) the peak voltage across the resistor is equal to the peak voltage across the inductor.
B) the peak voltage across the resistor is equal to the peak voltage across the capacitor.
C) the peak voltage across the capacitor is greater than the peak voltage across the inductor.
D) the current is in phase with the driving voltage.
E) the peak voltage across the inductor is greater than the peak voltage across the capacitor.

Question 23

A 120 V-rms voltage is applied across a 6.0-μF capacitor and a 100-Ω resistor. If the frequency of the generator is 60 Hz, what is the rms value of the current in the circuit?

A) 0.26 A
B) 0.36 A
C) 0.46 A
D) 0.56 A
E) 0.76 A

Question 24

In a RLC circuit, the values of the inductance and capacitance are both halved. In comparison with the resonance frequency of the original circuit, the new resonant frequency will be

A) the same as before.
B) reduced to one-half the original value.
C) reduced to one-quarter the original value.
D) increased by a factor of two.
E) increased by a factor of four.

Question 25

A pure inductor is connected to an AC power supply. In this circuit, the current

A) leads the voltage by 90°.
B) is in phase with the voltage.
C) lags the voltage by 45°.
D) lags the voltage by 90°.
E) leads the voltage by 45°.

Question 26

Consider a series circuit in which the capacitive reactance equals the inductive reactance. What is the phase angle between current and voltage?

A) +180.°
B) +90.°
C) -180.°
D) -90.°
E) 0.°

Question 27

In a RLC circuit, a second capacitor is connected in parallel with the capacitor previously in the circuit. What is the effect of this change on the impedance of the circuit?

A) It increases.
B) It decreases.
C) It does not change.
D) It increases for frequencies below resonance and decreases for frequencies above resonance.
E) It decreases for frequencies below resonance and increases for frequencies above resonance.

Question 28

The circuit power factor of an RL circuit connected across an ac source is one. What would be a good description of the frequency of this source?

A) Low
B) Very low
C) High
D) Very high

Question 29

A 120-V rms voltage is applied across a 6.00-μF capacitor and a 100-Ω resistor. If the frequency of the generator is 60.0 Hz, what is the impedance of this circuit?

A) 153 Ω
B) 453 Ω
C) 353 Ω
D) 253 Ω
E) 553 Ω

Question 30

The capacitive reactance of a 44-μF capacitor in an ac circuit is 6.0 × 10² Ω. What is the frequency of the applied signal?

A) 80 Hz
B) 17 Hz
C) 800 Hz
D) 6.0 Hz
E) 2.2 Hz

Question 31

The maximum voltage of an ac signal is 8.0 V. What is the rms value of this voltage?

A) 2.8 V
B) 5.7 V
C) 6.2 V
D) 4.0 V
E) 16.0 V

Question 32

What is the phase angle between the voltages of the inductor and capacitor in a RLC series circuit?

A) zero
B) 45°
C) 90°
D) 180°
E) 270°

Question 33

A 120-V rms voltage is applied across a 6.0-μF capacitor. If the frequency of the generator is 60 Hz, what is the rms value of the current in the circuit?

A) 0.47 A
B) 0.37 A
C) 0.071 A
D) 0.17 A
E) 0.27 A

Question 34

Consider an RLC series circuit. The impedance of the circuit increases if X_C increases.

A) true only if X_L is greater than or equal to X_C
B) true only if X_L is less than or equal to X_C
C) always true
D) never true

Question 35

In a RLC circuit, the values of the inductance and capacitance are both doubled. In comparison with the resonance frequency of the original circuit, the new resonant frequency will be

A) the same as before.
B) reduced to one-half the original value.
C) reduced to one-quarter the original value.
D) increased by a factor of two.
E) increased by a factor of four.

Question 36

A resistor and a capacitor are connected in series to an ideal battery of constant terminal voltage. When this system reaches its steady-state, the voltage across the resistor is

A) greater than the battery's terminal voltage.
B) equal to the battery's terminal voltage.
C) less than the battery's terminal voltage, but greater than zero.
D) zero.

Question 37

A 120-V rms voltage at 90 Hz is applied across a 20-μF capacitor and a 100-Ω resistor. What is the rms value of the current in that circuit?

A) 0.6 A
B) 0.7 A
C) 0.8 A
D) 0.9 A
E) 1.0 A

Question 38

In a RLC circuit, a second capacitor is connected in series with the capacitor previously in the circuit. What is the effect of this change on the impedance of the circuit?

A) It increases.
B) It decreases.
C) It does not change.
D) It increases for frequencies below resonance and decreases for frequencies above resonance.
E) It decreases for frequencies below resonance and increases for frequencies above resonance.

Question 39

A 6.0-μF capacitor is connected to an ac signal with a frequency of 60 Hz. If the maximum voltage applied to the capacitor is 8.0 V, what is the capacitive reactance?

A) 6.0 Ω
B) 440 Ω
C) 7.5 × 10^-6 Ω
D) 740 Ω
E) 160 Ω

Question 40

FIGURE 24-2
Figure 24-2 shows a simple ac circuit consisting of an inductor connected across the terminals of an ac generator. If the frequency of the ac generator is decreased by a factor of four, what will happen to the inductive reactance on the inductor?

A) It decreases by a factor of four.
B) It decreases by a factor of eight.
C) It increases by a factor of two.
D) It increases by a factor of four.
E) It increases by a factor of eight.

Question 41

A 120-V rms signal at 60 Hz is applied across a 30-mH inductor and a 100-Ω resistor. What is the rms value of the current in this circuit?

A) 0.80 A
B) 1.2 A
C) 1.4 A
D) 1.6 A
E) 1.8 A

Question 42

A total impedance of an RC circuit with a capacitance of 40.0 μF is 800 Ω. If the frequency of the applied ac voltage is 18.0 Hz, what is the resistance of the circuit?

A) 569 Ω
B) 669 Ω
C) 769 Ω
D) 869 Ω
E) 800 Ω

Question 43

A 120-V rms voltage at 60 Hz is applied across an RC circuit. The rms value of the current in the circuit is 0.60 A and it leads the voltage by 60°. What is the value of the resistance in this circuit?

A) 100 Ω
B) 150 Ω
C) 120 Ω
D) 60 Ω
E) 200 Ω

Question 44

The inductive reactance of a 20-mH inductor at a certain frequency is 120 Ω. What is the frequency in rad/s?

A) 2000 rad/s
B) 4000 rad/s
C) 5000 rad/s
D) 6000 rad/s
E) 7000 rad/s

Question 45

A 120-V rms signal at 60.0 Hz is applied across a 30.0-mH inductor and a resistor. If the rms value of the current in this circuit is 0.600 A, what is the value of the resistor?

A) 80.0 Ω
B) 268 Ω
C) 143 Ω
D) 200 Ω
E) 30.0 Ω

Question 46

The total impedance of an RC circuit with a resistance of 200 Ω is 1060 Ω. If the frequency of the applied voltage is 20.0 Hz, what is the value of the capacitance in this circuit?

A) 6.64 μF
B) 7.64 μF
C) 8.64 μF
D) 9.64 μF
E) 200 μF

Question 47

A 120-V rms voltage at 60 Hz is applied across an inductor and a 200-Ω resistor. If the impedance of this circuit is 216 Ω, what is the rms value of the current?

A) 0.336 A
B) 0.446 A
C) 0.556 A
D) 0.667 A
E) 0.767 A

Question 48

The circuit power factor of an RC circuit is 0.620. The rms value of the voltage applied to this signal is 120 V and the impedance is 200 Ω. What is the average power of this circuit?

A) 44.6 W
B) 89.2 W
C) 60.0 W
D) 0.620 W
E) 124 W

Question 49

A capacitor with a capacitive reactance of 40.0 Ω is connected in series with a 100-Ω resistor across an ac source of frequency 60.0 Hz. What is the phase angle?

A) +68.2°
B) -68.2°
C) -21.8°
D) +21.8°
E) 90.0°

Question 50

A 120-V rms signal at 60.0 Hz is applied across a 30.0-mH inductor and a 100-Ω resistor. What is the rms value of the voltage across the resistor?

A) 119 V
B) 60.0 V
C) 100 V
D) 110 V
E) 0.700 V

Question 51

A 120-V rms voltage at 60.0 Hz is applied across a capacitor and a 100-Ω resistor. If the impedance of this circuit is 200 Ω, what is the average power of this circuit?

A) 278 W
B) 72.0 W
C) 36.0 W
D) 100 W
E) 200 W

Question 52

A 120-V rms voltage at 1000 Hz is applied to a resistor and an inductor in series. If the impedance of this circuit is 110 Ω, what is the maximum value of the current?

A) 1.54 A
B) 1.09 A
C) 1.84 A
D) 1.04 A
E) None of the other answers is correct.

Question 53

A 60.0-μF capacitor is in series with a 100-Ω resistor connected across an ac source of frequency 120 Hz. What is the phase angle?

A) -12.4°
B) +12.4°
C) -77.6°
D) +77.6°
E) 90.0°

Question 54

A 100-Ω resistor is connected in series with a 10-mH inductor across an ac source operating at 1000 Hz. What is the impedance of this circuit?

A) 100 Ω
B) 118 Ω
C) 200 Ω
D) 236 Ω
E) 1000 Ω

Question 55

A 120-V rms voltage at 60 Hz is applied across an RC circuit. The rms value of the current in the circuit is 0.60 A and it leads the voltage by 60°. What is the value of the capacitance in this circuit?

A) 13 μF
B) 14 μF
C) 15 μF
D) 16 μF
E) 17 μF

Question 56

What is the inductive reactance of a 20-mH inductor at a frequency of 60 Hz?

A) 7.5 Ω
B) 0.13 Ω
C) 1.2 Ω
D) 1.2 mΩ
E) 7.5 mΩ

Question 57

The inductive reactance of a 20.0-mH inductor at a certain frequency is 120 Ω. What is the frequency in Hz?

A) 120 Hz
B) 167 Hz
C) 478 Hz
D) 6000 Hz
E) 955 Hz

Question 58

A 120-V rms voltage at 60 Hz is applied across a 20-μF capacitor and an unknown resistor. If the rms value of the current in that circuit is 0.60 A, what is the value of the resistor?

A) 60 Ω
B) 120 Ω
C) 180 Ω
D) 150 Ω
E) 200 Ω

Question 59

The power factor of an RL circuit with a 100-Ω resistor and a certain inductor is 0.60. What is the impedance of the circuit?

A) 170 Ω
B) 85 Ω
C) 340 Ω
D) 100 Ω
E) 60 Ω

Question 60

At what frequency will a 20.00-mH inductor have an inductive reactance of 100.0 Ω?

A) 225.4 Hz
B) 654 .8 Hz
C) 795.7 Hz
D) 457.4 Hz
E) None of the other answers is correct.

Question 61

A 120-V rms signal at 60.0 Hz is applied across a 30.0-mH inductor and a 100-Ω resistor. What is the rms value of the voltage across the inductor?

A) 0.700 V
B) 119 V
C) 100 V
D) 13.5 V
E) 120 V

Question 62

A 120-V rms voltage at 60.0 Hz is applied across an inductor, a capacitor, and a resistor in series. If the rms value of the current in this circuit is 0.600 A, what is the impedance of this circuit?

A) 200 Ω
B) 141 Ω
C) 20 4 Ω
D) 120 Ω
E) 100 Ω

Question 63

What inductance must be put in series with a 200-Ω resistor at 4000 Hz to have a total impedance of 240 Ω?

A) 3.28 mH
B) 4.28 mH
C) 5.28 mH
D) 6.28 mH
E) 12 mH

Question 64

An ac signal at a certain frequency is applied across a 40-mH inductor and a 100-Ω resistor. If the power factor of this circuit is 0.40, what is the value of the frequency?

A) 160 Hz
B) 200 Hz
C) 410 Hz
D) 600 Hz
E) 910 Hz

Question 65

A certain ac signal at 1000 Hz is applied across an inductor and a 100-Ω resistor. If the power factor of the circuit is 0.400, what is the impedance of this circuit?

A) 150 Ω
B) 200 Ω
C) 250 Ω
D) 100 Ω
E) 300 Ω

Question 66

A 20.0-mH inductor is connected in series with a 100-Ω resistor at 1000 Hz. What is the phase angle of this circuit?

A) 90.0°
B) 51.5°
C) 38.5°
D) 0°
E) 45°

Question 67

What resistance must be put in series with a 30-mH inductor at 4000 Hz to have a total impedance of 8.0 × 10⁴ Ω?

A) 30 × 10⁴ Ω
B) 5.0 × 10⁴ Ω
C) 6.0 × 10⁴ Ω
D) 7.0 × 10⁴ Ω
E) 8.0 × 10⁴ Ω

Question 68

The phase angle of an RLC series circuit with an inductive reactance of 200 Ω, a resistor of 200 Ω and a certain capacitor at 1000 Hz is 40.0°. What is the value of the capacitance in this circuit?

A) 1.95 μF
B) 2.95 μF
C) 3.95 μF
D) 4.95 μF
E) 5.95 μF

Question 69

A 120-V rms voltage at 60.0 Hz is applied across an inductor, capacitor and a 100-Ω resistor in series. If the maximum value of the current in this circuit is 1.60 A, what is the rms value of the current in this circuit?

A) 1.13 A
B) 2.26 A
C) 1.82 A
D) 1.60 A
E) 2.66 A

Question 70

The phase angle of a series RL circuit with a 100.0-Ω resistor and a 20.00-mH inductor is 70.00°. What is the inductive reactance of this circuit?

A) 100.0 Ω
B) 150.0 Ω
C) 200.0 Ω
D) 174.7 Ω
E) 274.7 Ω

Question 71

A 25.0-mH inductor, a 2.00-μF capacitor, and a certain resistor are connected in series across an ac voltage source at 1000 Hz. If the impedance of this circuit is 200 Ω, what is the value of the resistor?

A) 100 Ω
B) 184 Ω
C) 552 Ω
D) 579 Ω
E) 200 Ω

Question 72

The phase angle of an RLC series circuit with a capacitive reactance of 40 Ω, a resistor of 100 Ω and a certain inductor at 1000 Hz is 40.0°. What is the value of the inductance in this circuit?

A) 11.8 mH
B) 124 mH
C) 212 mH
D) 61.9 mH
E) 19.7 mH

Question 73

The phase angle in a series RL circuit at 1000 Hz with a 200-Ω resistor and a certain inductor is 40.0°. What is the value of the inductance in this circuit?

A) 83.9 mH
B) 73.9 mH
C) 26.7 mH
D) 36.7 mH
E) 57.9 mH

Question 74

A 200-Ω resistor, a 25-mH inductor, and a capacitor are connected in series across an ac voltage source at 1000 Hz. If the impedance of this circuit is 240 Ω, what is the value of the capacitor?

A) 5.5 μF
B) 3.2 μF
C) 4.2 μF
D) 6.5 μF
E) 7.5 μF

Question 75

A 50.0-mH inductor is connected in series with a 2500-Ω resistor. What is the phase angle at 3000 Hz?

A) 20.7°
B) - 20.7°
C) -75.9°
D) 75.9°
E) 90.0°

Question 76

A 200-Ω resistor, 40.0-mH inductor and a 2.00-μF capacitor are connected in series with a 120-V rms source at 1000 Hz. What is the phase angle of this circuit?

A) 49.3°
B) 90.0°
C) 40.7°
D) 0°
E) 45.0°

Question 77

The phase angle of a series RL circuit with a 20.0-mH inductor and a certain resistor at 1000 Hz is 20.0°. What is the value of the resistance in this circuit?

A) 145 Ω
B) 100 Ω
C) 245 Ω
D) 200 Ω
E) 345 Ω

Question 78

The phase angle of an RLC series circuit with an inductive reactance of 200 Ω and a capacitive reactance of 100 Ω is 40.0°. What is the value of the resistor in this circuit?

A) 100 Ω
B) 119 Ω
C) 156 Ω
D) 200 Ω
E) 265 Ω

Question 79

A 200-Ω resistor, a 40.0-mH inductor and a 2.00-μF capacitor are connected in series with a 120-V rms source at 1000 Hz. What is the impedance of this circuit?

A) 164 Ω
B) 120 Ω
C) 264 Ω
D) 200 Ω
E) 364 Ω

Question 80

A certain ac signal at 60 Hz is applied across a 40-mH inductor and a 200-Ω resistor. What is the power factor of this circuit?

A) 0.249
B) 0.497
C) 0.697
D) 0.997
E) None of the other answers is correct.