Deck 21: Alternating Current

Question 1

What is the capacitive reactance of an 8.00 $\mu$ F V capacitor attached to 120 V rms at 60.0 Hz?

A) 166 $\Omega$
B) 332 $\Omega$
C) 663 $\Omega$
D) 480 $\Omega$
E) 960 $\Omega$

Answer 1

332 $\Omega$

Question 2

The voltage supplied to an ac circuit is given by v = 120 sin(377t).What is the voltage at t = 3.00 $\times$ 10^-3 s?

A) 0.00 V
B) 2.37 V
C) 63.0 V
D) 109 V
E) 119 V

Answer 2

109 V

Question 3

A 2.2 k $\Omega$ resistor and a 2.0 $\mu$ F capacitor are in series in an ac circuit.The rms voltages across each are equal.What is the frequency?

A) 23 Hz
B) 15 Hz
C) 72 Hz
D) 36 Hz
E) There is insufficient information to solve.

Answer 3

36 Hz

Question 4

The voltage supplied to an ac circuit is given by v = 120 sin(60t).What are the rms voltage and the frequency?

A) 120 V, 60 Hz
B) 120 V, 380 Hz
C) 170 V, 9.5 Hz
D) 85 V, 9.5 Hz
E) 240 V, 30 Hz

Question 5

A 150 W light bulb is operating on a 120 V rms ac line.What is the rms current in the bulb?

A) 2.50 A
B) 1.67 A
C) 1.50 A
D) 1.25 A
E) 0.883 A

Question 6

The difference between the highest and lowest voltage of a household "120 V emf" is

A) 120 V.
B) 170 V.
C) 240 V.
D) 340 V.
E) 377 V.

Question 7

What is the average power for an 8.00 mF capacitor attached to a 120 V rms 60.0 Hz source?

A) 240 W
B) 120 W
C) 85.0 W
D) 60.0 W
E) 0.000

Question 8

A bulb is designed for 100 W at 130 V rms.What is the power dissipated by this bulb if it is used in a 120 V rms circuit?

A) 169 W
B) 130 W
C) 100 W
D) 85.0 W
E) it will blow out

Question 9

Two 100 W bulbs differ in that one is designed for the American 120 V rms and the other is designed for the European 220 V rms.Which bulb has the greater resistance,and what is that resistance?

A) American,288 $\Omega$
B) American,144 $\Omega$
C) European,484 $\Omega$
D) European,242 $\Omega$
E) they are the same,265 $\Omega$

Question 10

What is the rms current for an 8.0 $\mu$ F capacitor attached to a 120 V rms 60 Hz source?

A) 2.8 A
B) 1.4 A
C) 0.72 A
D) 0.36 A
E) 0.18 A

Question 11

The average value of sin² $\omega$ t for a complete cycle is

A) 1.
B) 0.
C) 0.707.
D) 0.500.
E) 0.250.

Question 12

A lightbulb is connected to a 120 V(rms),60 Hz source.How many times per second does the current reverse directions?

A) 60
B) 130
C) 120
D) 30

Question 13

What is the capacitance of a capacitor with a reactance of 20.0 $\Omega$ at a frequency of 60.0 Hz?

A) 50.0 mF
B) 50.0 $\mu$ F
C) 133 mF
D) 133 $\mu$ F
E) 833 $\mu$ F

Question 14

What is maximum number 150 W light bulbs that can run on a 130 V circuit protected by a 20 amp circuit breaker?

A) 18
B) 16
C) 17
D) 15

Question 15

For a capacitor in and ac circuit,how much energy is stored in the capacitor at the instant when current is zero?

A) 0.707 maximum
B) half
C) zero
D) maximum

Question 16

A 1500 W hair dryer is run on a 120 V rms circuit.If the circuit breaker is chosen from breakers with the ratings below,which is the lowest-rated current breaker of the following that won't open the circuit?

A) 10 A
B) 15 A
C) 20 A
D) 30 A
E) 60 A

Question 17

What is the peak (maximum)power dissipated by a 150 W light bulb attached to a 120 V rms ac line?

A) 301 W
B) 212 W
C) 150 W
D) 106 W
E) 75.0 W

Question 18

In an ac circuit,the current in a capacitor

A) leads the voltage by 90 ^$\circ$ .
B) lags the voltage by 90 ^$\circ$ .
C) is in phase with the voltage.
D) leads the voltage by $\pi$ radians.
E) lags the voltage by $\pi$ radians.

Question 19

A 150 W light bulb is designed for an ac voltage of 120 V rms.What is the resistance of the bulb?

A) 150 $\Omega$
B) 144 $\Omega$
C) 96.0 $\Omega$
D) 68.0 $\Omega$
E) 48.0 $\Omega$

Question 20

What is the period for a frequency of 60 Hz?

A) 60 s
B) (1/60)s
C) 120 s
D) (1/120)s
E) (1/377)s

Question 21

A series RLC ac circuit has a capacitive reactance of 55 $\Omega$ ,and inductive reactance of 25 $\Omega$ ,and a resistance of 40 $\Omega$ .What is the impedance of this circuit?

A) 12 $\Omega$
B) 95 $\Omega$
C) 70 $\Omega$
D) 10 $\Omega$
E) 50 $\Omega$

Question 22

A capacitor is connected to the terminals of a variable frequency oscillator.The peak voltage of the source in kept fixed while the frequency is increased.Which statement is true?

A) The rms current through the capacitor decreases.
B) The rms current through the capacitor increases.
C) The phase angle between the current and source voltage changes.
D) The current becomes zero when the frequency is large enough.

Question 23

What is the inductance for an inductor with a reactance of 20 $\Omega$ at a frequency of 60 Hz?

A) 12 H
B) 19 H
C) 3.0 H
D) 53 mH
E) 27 mH

Question 24

A series RLC circuit has R = 200 $\Omega$ , L = 40.0 mH, and C = 120 pF.What is the impedance of this circuit at resonance?

A) 18.0 k $\Omega$
B) 36.0 k $\Omega$
C) 400 $\Omega$
D) 300 $\Omega$
E) 200 $\Omega$

Question 25

What is the rms current in a 200 mH inductor attached to a 120 V rms 60.0 Hz source?

A) 600 A
B) 12.0 A
C) 1.59 A
D) 100 A
E) 1.00 A

Question 26

In an ac circuit,the current in an inductor

A) leads the voltage by 90 ^$\circ$ .
B) lags the voltage by 90 ^$\circ$ .
C) is in phase with the voltage.
D) leads the voltage by $\pi$ radians.
E) lags the voltage by $\pi$ radians.

Question 27

A series RLC ac circuit has a capacitive reactance of 55 $\Omega$ , and inductive reactance of 25 $\Omega$ , and a resistance of 40 $\Omega$ .What is the phase constant of this circuit?

A) 37 $^{\circ}$
B) -37 $^{\circ}$
C) 53 $^{\circ}$
D) -53 $^{\circ}$
E) 66 $^{\circ}$

Question 28

An ac circuit has a resistance of 120 $\Omega$ and an impedance of 200 $\Omega$ .What is the power factor for this circuit?

A) 53 $^{\circ}$
B) 32 $^{\circ}$
C) 0.60
D) 1.7
E) 1.3

Question 29

At what frequency is the reactance of a 20.0 mH inductor equal to 18.8 $\Omega$ .

A) 75.0 Hz
B) 150 Hz
C) 1500 Hz
D) 15.0 Hz

Question 30

A series LR circuit dissipates 60 W.The circuit is powered by a 120 V rms 60 Hz supply.If the current is 2.0 A rms,what is the circuit resistance?

A) 50 $\Omega$
B) 60 $\Omega$
C) 15 $\Omega$
D) 10 $\Omega$
E) 24 $\Omega$

Question 31

What capacitance is needed in series with a 30 $\Omega$ resistor at 1.0 kHz for a total impedance of 45 $\Omega$ ?

A) 34 $\mu$ F
B) 15 $\mu$ F
C) 4.7 $\mu$ F
D) 0.037 $\mu$ F

Question 32

The capacitive reactance of an RLC circuit is 64 $\Omega$ .If the frequency is doubled,what is the new capacitive reactance?

A) 18 $\Omega$
B) 64 $\Omega$
C) 32 $\Omega$
D) 8.0 $\Omega$
E) 4.0 $\Omega$

Question 33

What is the inductive reactance of a 200 mH inductor attached to a 120 V rms 60.0 Hz source?

A) 12.0 $\Omega$
B) 75.4 $\Omega$
C) 188 $\Omega$
D) 940 $\Omega$
E) 24.0 $\Omega$

Question 34

A series LR circuit dissipates 60 W.The circuit is powered by a 120 V rms 60 Hz supply.If the current is 2.0 A rms,what is the phase constant?

A) 14 $^{\circ}$
B) 25 $^{\circ}$
C) 60 $^{\circ}$
D) 70 $^{\circ}$
E) 76 $^{\circ}$

Question 35

An ac circuit has a 20 $\mu$ F capacitor,an 80 mH inductor,and a 60 $\Omega$ resistor in series.If the voltage source has an angular frequency of 1000 rad/s,what is the phase constant for the circuit?

A) 27 $^{\circ}$
B) 53 $^{\circ}$
C) 45 $^{\circ}$
D) 63 $^{\circ}$
E) 88 $^{\circ}$

Question 36

In an RLC ac circuit the current in the inductor and the current in the resistor are

A) out of phase by 90 $^{\circ}$ with the current in the inductor leading.
B) out of phase by 90 $^{\circ}$ with the current in the resistor leading.
C) in phase with each other.
D) out of phase by an amount proportional to frequency.
E) out of phase by an amount inversely proportional to frequency.

Question 37

For an ideal inductor in an ac circuit,how much energy is stored in the inductor at the instant when the current is zero?

A) maximum
B) 1/2 maximum
C) 0.707 maximum
D) zero

Question 38

A series LR circuit dissipates 60 W.The circuit is powered by a 120 V rms 60 Hz supply.If the current is 2.0 A rms,what is the inductance?

A) 0.10 H
B) 0.15 H
C) 0.20 H
D) 0.25 H
E) 0.30 H

Question 39

A series LR circuit dissipates 60 W.The circuit is powered by a 120 V rms 60 Hz supply.If the current is 2.0 A rms,what is the power factor?

A) 0
B) 0.25
C) 0.50
D) 0.75
E) 1.0

Question 40

If the power factor for a series RLC circuit is 1.00,what is the phase constant?

A) 0.0 $^{\circ}$
B) 30 $^{\circ}$
C) 45 $^{\circ}$
D) 60 $^{\circ}$
E) 90 $^{\circ}$

Question 41

An RLC series circuit has a 400 $\Omega$ resistance, a 2.5 mH inductor,and a capacitor.If the circuit is in resonance at 30 kHz and is attached to a 20 mV rms power supply,what is the rms voltage across the inductor?

A) 20 mV
B) 24 mV
C) 16 mV
D) 48 mV
E) 0.00

Question 42

A series RLC circuit has a resistance of 500 $\Omega$ , and inductance of 20.0 mH,and a capacitance of 2.00 $\mu$ F. The power source provides a voltage of v = (170 sin(377t))V. What is the impedance of this circuit?

A) 0.402 k $\Omega$
B) 1.33 k $\Omega$
C) 1.25 k $\Omega$
D) 1.41 k $\Omega$
E) 2.15 k $\Omega$

Question 43

An RLC series circuit has a 400 $\Omega$ resistance,a 2.5 mH inductor,and a capacitor.If the circuit is in resonance at 30 kHz and is attached to a 20 mV rms power supply,what is the power dissipated by the circuit?

A) 1.0 $\mu$ W
B) 2.0 $\mu$ W
C) 24 mW
D) 1.2 $\mu$ W
E) 1.2 mW

Question 44

What inductance is needed in series with a 4.7 $\mu$ F capacitor for a resonant frequency of 10 kHz?

A) 22 uH
B) 54 uH
C) 0.66 uH
D) 5.3 mH

Question 45

A series RLC circuit has resistance 200 $\Omega$ ,inductance 0.200 H, and capacitance 0.500 $\mu$ F.If the circuit is at resonance with a 120 V rms source,what is the average power dissipated?

A) 144 W
B) 120 W
C) 77.0 W
D) 72.0 W
E) 100 W

Question 46

In a series LRC circuit the rms voltage across the resistor is 80.0 V,across the capacitor is 120 V,and across the inductor is 60.0 V.If 1.50 A rms is flowing in this circuit,what is the average power dissipated?

A) 200 W
B) 120 W
C) 80.0 W
D) 60.0 W
E) 40.0 W

Question 47

The inductive reactance of an RLC circuit is 36 $\Omega$ .If the frequency is doubled,what is the new inductive reactance?

A) 72 $\Omega$
B) 36 $\Omega$
C) 19 $\Omega$
D) 6.0 $\Omega$
E) 3.0 $\Omega$

Question 48

An RLC series circuit has a 400 $\Omega$ resistance,a 2.5 mH inductor,and a capacitor.If the circuit is in resonance at 30 kHz,what is the capacitive reactance?

A) 4.0 $\times$ 10² $\Omega$
B) 6.2 $\times$ 10² $\Omega$
C) 4.7 $\times$ 10² $\Omega$
D) 71 $\Omega$
E) 0.00

Question 49

An RLC series circuit has a 200 $\Omega$ resistance,a 3.00 mH inductor,and a 100 $\mu$ F capacitor.What is the resonant frequency for this circuit?

A) 1.80 kHz
B) 1.80 MHz
C) 290 Hz
D) 290 kHz
E) 11.0 kHz

Question 50

I the inductance and the capacitance both double in an LRC series circuit,the resonate frequency of that circuit will

A) decrease by a factor of 1/2.
B) decrease by a factor of 1/4.
C) increase by a factor of 2.
D) increase by a factor of 4.

Question 51

In a series LRC circuit the rms voltage across the resistor is 80.0 V,across the capacitor is 120 V,and across the inductor is 60.0 V.What is the rms voltage applied to this circuit?

A) 60.0 V
B) 80.0 V
C) 100 V
D) 120 V
E) 140 V

Question 52

What is the resonant frequency of a 1.0 $\mu$ F capacitor and 15 mH coil in series?

A) 15 kHz
B) 1.3 kHz
C) 0.87 kHz
D) 57 kHz

Question 53

An RLC series circuit has a 200 $\Omega$ resistance,a 3.0 mH inductor,and a 100 $\mu$ F capacitor.At resonance,what is the inductive reactance?

A) 21 $\Omega$
B) 5.5 $\Omega$
C) 11 $\Omega$
D) 25 $\Omega$
E) 30 $\Omega$

Question 54

A series RLC circuit has a resistance of 500 $\Omega$ , and inductance of 20.0 mH, and a capacitance of 2.00 $\mu$ F. The power source provides a voltage of v = (170 sin(377t))V. What is the peak current in this circuit?

A) 92.4 mA
B) 101 mA
C) 121 mA
D) 170 mA
E) 240 mA

Question 55

A series RLC circuit has a capacitive reactance of 16 $\Omega$ and an inductive reactance of 4.0 $\Omega$ at 30 Hz.What frequency would result in resonance for this circuit?

A) 12 Hz
B) 60 Hz
C) 15 Hz
D) 7.5 Hz
E) Resonance is not possible in this case.

Question 56

An ideal diode in an ac circuit

A) doubles the current.
B) halves the current.
C) permits the current to flow in only one direction.
D) permits the current to flow in one direction and double the current to flow in the other.
E) permits the current to flow in one direction and half the current to flow in the other.

Question 57

An RLC series circuit has a 22 $\Omega$ resistor,a 3.0 H inductor,and a capacitor.What capacitance would result in resonance at 60 Hz?

A) 55 mF
B) 0.33 F
C) 65 $\mu$ F
D) 15 mF
E) 2.3 $\mu$ F

Question 58

An RLC series circuit has a 400 $\Omega$ resistance,a 2.50 mH inductor,and a capacitor.If the circuit is in resonance at 30.0 kHz and is attached to a 20 mV rms power supply,what is the rms current?

A) 60 $\mu$ A
B) 40 $\mu$ A
C) 30 $\mu$ A
D) 50 $\mu$ A
E) 25 $\mu$ A

Question 59

As the ac frequency in an RLC circuit is increased to very high values,which of the contributions to the impedance dominates?

A) the capacitive reactance
B) the inductive reactance
C) the resistance
D) the combined capacitive reactance and the resistance
E) More information is needed.

Question 60

In a series LRC circuit the rms voltage across the resistor is 80 V,across the capacitor is 120 V,and across the inductor is 60 V.What is the phase constant for this circuit?

A) 27 $^{\circ}$
B) -27 $^{\circ}$
C) 37 $^{\circ}$
D) -37 $^{\circ}$
E) -41 $^{\circ}$

Question 61

The power dissipated in an RLC series circuit is dependent upon:

A) the impedance
B) the capacitive reactance
C) the inductive reactance
D) the resistance

Question 62

As frequency is varied in an RLC series circuit,resonance is reached when

A) the impedance becomes zero.
B) the inductive reactance is equal to the capacitive reactance.
C) the sum of the inductive and capacitive reactances is equal to the resistance.
D) the capacitive reactance is equal to the resistance.
E) the inductive reactance is equal to the resistance.

Question 63

If an AC circuit consists of a 220 mH inductor in series with a 25 pF capacitor and an AC generator with rms voltage of 12 V.At what frequency will the rms voltage drop across the capacitor be equal to that across the inductor?

A) 94 kHz
B) 15 kHz
C) 68 kHz
D) 426 kHz

Question 64

The current in an RLC circuit when driven at resonance depends on

A) the resonance frequency.
B) the resistance.
C) the inductive reactance.
D) the capacitive reactance.
E) More than one of these choices are correct.

Question 65

If an AC circuit consists of a 220 mH inductor in series with a 25 pF capacitor and an AC generator with rms voltage of 12 V.If the frequency of the generator is 55 kHz,what will the rms voltage drop across the inductor be?

A) 5.4 V
B) 11.80 V
C) 6.6 V
D) 0.20 V

Question 66

As frequency is varied in an RLC series circuit,resonance is reached when

A) the voltages V_R,V_L and V_C all become equal.
B) the voltages V_L and V_C become zero.
C) the voltage V_R becomes equal to the source voltage.
D) None of the choices are correct.

Question 67

If an AC circuit consists of a 220 mH inductor in series with a 75 k $\Omega$ resistor and an AC generator with rms voltage of 12 V.At what frequency will the rms voltage drop across the resistor be equal to that across the inductor?

A) 114 kHz
B) 5.5 kHz
C) 875 Hz
D) 18 kHz

Question 68

If an AC circuit consists of a 220 mH inductor in series with a 75 k $\Omega$ resistor and an AC generator with rms voltage of 12 V.If the frequency of the generator is 25 kHz,what is the rms voltage drop across the inductor?

A) 7.0 V
B) 2.6 V
C) 9.4 V
D) 5.0 V

Question 69

A 25 nH inductor is in an AC circuit whose generator has an rms voltage of 12 V.At what frequency must the generator drive the circuit if the rms current is to be 2.0 mA?

A) 0.15 MHz
B) 38 GHz
C) 0.96 MHz
D) 240 GHz

Question 70

If an AC circuit consists of a 220 mH inductor in series with a 25 pF capacitor and an AC generator with rms voltage of 12 V.If the frequency of the generator is 55 kHz,what will the rms voltage drop across the capacitor be?

A) 5.4 V
B) 0.20 V
C) 6.6 V
D) 11.80 V

Question 71

The power factor of an RLC series circuit _______ at resonance.

A) is one
B) has a value that depends upon the ratio of inductive reactance to impedance
C) has a value that depends upon the ratio of capacitive reactance to impedance
D) is zero

Question 72

If an AC circuit consists of a 220 mH inductor in series with a 75 k $\Omega$ resistor and an AC generator with rms voltage of 12 V.If the frequency of the generator is 25 kHz,what is the rms voltage drop across the resistor?

A) 7.0 V
B) 9.4 V
C) 2.6 V
D) 5.0 V

Question 73

In an RLC series circuit,which of the following statements is true?

A) The current is in phase with the voltage across the inductor.
B) The current is in phase with the voltage across the resistor.
C) The current is in phase with the voltage across the capacitor.
D) None of the choices are true.