Deck 24: Alternating-Current Circuits

Question 1

As the frequency of the ac voltage across an inductor approaches zero,the inductive reactance of that coil

A)approaches zero.
B)approaches one.
C)approaches infinity.
D)becomes negative.

Answer 1

approaches zero.

Question 2

If 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

Answer 2

5.7 V

Question 3

What size capacitor must be placed in series with a 40-mH coil so the circuit will oscillate with a frequency of 1000 Hz?

A)0.63 μF
B)0.50 μF
C)0.22 μF
D)0.17 μF

Answer 3

0.63 μF

Question 4

A simple ac circuit is composed of a capacitor connected across the terminals of an ac power source.If the frequency of the source is doubled,what happens to the 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 5

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 are correct.

Question 6

A series circuit contains an 80-μF capacitor,a 0.020-H inductor,and a switch.The resistance of the circuit is negligible.Initially,the switch is open,the capacitor voltage is 50 V,and the current in the inductor is zero.At time t = 0 s,the switch is closed.What is the maximum current in the circuit?

A)2.2 A
B)2.4 A
C)2.8 A
D)3.0 A
E)3.2 A

Question 7

A simple circuit consists only of of a 1.0-μF capacitor and a 15-mH coil in series.At what frequency will this circuit oscillate?

A)15 kHz
B)1.3 kHz
C)0.77 kHz
D)67 Hz

Question 8

A simple ac circuit consists of an inductor connected across the terminals of an ac power source.If the frequency of the ac source is decreased by a factor of four,what happens to the reactance of 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 9

A series circuit contains an 80-μF capacitor,a 0.020-H inductor,and a switch.The resistance of the circuit is negligible.Initially,the switch is open,the capacitor voltage is 50 V,and the current in the inductor is zero.At time t = 0 s,the switch is closed.When the current in the circuit is 1.5 A,what is the charge on the capacitor?

A)2000 µC
B)2500 µC
C)3000 µC
D)3500 µC
E)4000 µC

Question 10

Which of the following statements is true for a series RLC ac circuit in resonance? (There could be more than one correct choice).

A)The inductive reactance and the capacitive reactance are both equal to zero.
B)The inductive reactance is equal to the capacitive reactance.
C)The current in the circuit is a minimum.
D)The current in the circuit is a maximum.
E)The rms current is equal to the peak current.

Question 11

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

A)0°
B)45°
C)90°
D)180°
E)270°

Question 12

In an RLC ac circuit,the values of the inductance and capacitance are both doubled.As a result of this change,the resonance frequency of the circuit is

A)the same as before.
B)reduced to one-half the original value.
C)reduced to one-fourth the original value.
D)twice the original value.
E)four times the original value.

Question 13

A series circuit contains an 80-μF capacitor,a 0.020-H inductor,and a switch.The resistance of the circuit is negligible.Initially,the switch is open,the capacitor voltage is 50 V,and the current in the inductor is zero.At time t = 0 s,the switch is closed.When the potential across the capacitor is 30 V,what is the rate of change of the current?

A)1000 A/s
B)1500 A/s
C)2000 A/s
D)2500 A/s
E)3000 A/s

Question 14

What inductance is needed in series with a 4.7-μF capacitor so the circuit will oscillate at a frequency of 10 kHz?

A)21 μH
B)54 μH
C)4.7 mH
D)5.4 mH

Question 15

In the figure,which of the phasor diagrams represents a series RLC circuit driven at resonance?

A)1
B)2
C)3
D)4
E)5

Question 16

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 17

Consider a capacitor connected across the ac source.As the capacitance is increased,the current through the capacitor will

A)increase.
B)remain constant.
C)decrease.

Question 18

In a RLC circuit,the values of the inductance and capacitance are both halved.As a result of this change,the resonance frequency of the circuit is

A)the same as before.
B)reduced to one-half the original value.
C)reduced to one-fourth the original value.
D)twice the original value.
E)four times the original value.

Question 19

A series circuit contains an 80-μF capacitor,a 0.020-H inductor,and a switch.The resistance of the circuit is negligible.Initially,the switch is open,the capacitor voltage is 50 V,and the current in the inductor is zero.At time t = 0 s,the switch is closed.How long after closing the switch does the magnetic energy in the inductor first reach its maximum value?

A)2.0 ms
B)4.0 ms
C)6.0 ms
D)8.0 ms
E)10 ms

Question 20

What capacitance is needed in series with a 3.7-mH inductor so the circuit will oscillate at a frequency of 1000 Hz?

A)0.15 mF
B)15 μF
C)6.8 μF
D)0.015 μF

Question 21

The current through a 50-Ω resistor is I = (0.80 A) sin(240t),where t is measured in seconds. How much power on average is dissipated in the resistor?

A)16 W
B)32 W
C)45 W
D)64 W

Question 22

What is the rms current through a 0.0010-μF capacitor at 1000 Hz and 5.0 V?

A)5.4 μA
B)31 μA
C)3.1 mA
D)10 mA

Question 23

The reactance of a capacitor is
At a frequency of
What is the capacitance?

A)0.066 μF
B)0.42 μF
C)2.6 μF
D)0.093 μF

Question 24

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 its capacitive reactance?

A)6.0 Ω
B)440 Ω
C)7.5 × Ω
D)740 Ω
E)160 Ω

Question 25

In the circuit shown in the figure,the 60-Hz ac source has a voltage amplitude of 120 V,the capacitive reactance is
The inductive reactance is
And the resistance is
What is the capacitance C of the capacitor?

A)3.2 µF
B)6.3 µF
C)9.4 µF
D)13 µF
E)20 µF

Question 26

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 27

At what frequency will the capacitive reactance of a 0.010-μF capacitor be 100 Ω?

A)1.0 kHz
B)16 kHz
C)0.16 MHz
D)0.31 MHz

Question 28

A 10-Ω resistor is connected to a 120-V ac power supply.What is the peak current through the resistor?

A)12 A
B)17 A
C)0.083 A
D)0.12 A

Question 29

What is the peak voltage in an ac circuit where the rms voltage is 120 V?

A)84.8 V
B)120 V
C)170 V
D)240 V

Question 30

What is the inductive reactance of a 2.50-mH coil at 1000 Hz?

A)2500 Ω
B)796 Ω
C)15.7 Ω
D)2.50 Ω

Question 31

What is the reactance of a 1.0-mH inductor at 60 Hz?

A)0.19 Ω
B)0.38 Ω
C)2.7 Ω
D)5.3 Ω

Question 32

An alternating current is supplied to an electronic component with a rating that the voltage across it can never,even for an instant,exceed 16 V.What is the highest rms voltage that can be supplied to this component while staying below the voltage limit?

A)8 V
B)16 V
C)256 V
D)8 V

Question 33

At what frequency is the reactance of a 20.0-mH inductor equal to 120 Ω?

A)318 Hz
B)637 Hz
C)796 Hz
D)955 Hz
E)1110 Hz

Question 34

The current through a 50-Ω resistor is I = (0.80 A) sin(240t),where t is measured in seconds.What is the rms current?

A)0.57 A
B)0.80 A
C)1.1 A
D)1.6 A

Question 35

The capacitive reactance of a 44-μF capacitor in an ac circuit is 6.0 ×
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 36

A 150-W lamp is placed into a 120-V ac outlet.What is the peak current?

A)0.80 A
B)0.88 A
C)1.2 A
D)1.8 A

Question 37

What is the 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 38

At what frequency does a 10-μF capacitor have a reactance of 1200 Ω?

A)13 Hz
B)42 Hz
C)60 Hz
D)83 Hz

Question 39

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 40

In the circuit shown in the figure,the 60-Hz ac source has a voltage amplitude of 120 V,the capacitive reactance is
The inductive reactance is
And the resistance is
What is the inductance L of the inductor?

A)770 mH
B)1,700 mH
C)2,900 mH
D)3,700 mH
E)4,800 mH

Question 41

A series circuit has a sinusoidal voltage supplied to it at
With a peak voltage of
It also contains a
Resistance,a
Capacitance,and a
Inductance.What is the peak current for this circuit?

A)6.3 μA
B)11 μA
C)26 μA
D)30 μA

Question 42

A 120-V rms signal at 60.0 Hz is applied across a series combination of 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 43

At what frequency will a 14.0-mH coil have 14.0 Ω of inductive reactance?

A)1000 Hz
B)505 Hz
C)257 Hz
D)159 Hz

Question 44

At what frequency will a 20.0-mH inductor have an inductive reactance of 100 Ω?

A)225 Hz
B)655 Hz
C)796 Hz
D)457 Hz
E)None of the other answers is correct.

Question 45

The figure shows a series ac circuit.The inductor has a reactance of 50 Ω and an inductance of 220 mH.An 80-Ω resistor and a capacitor whose reactance is 160 Ω are also in the circuit,and the rms current in the circuit is 2.2 A.What is the voltage amplitude across the capacitor?

A)500 V
B)350 V
C)630 V
D)770 V
E)210 V

Question 46

In the circuit shown in the figure,the 60-Hz ac source has a voltage amplitude of 120 V,the capacitive reactance is
The inductive reactance is
And the resistance is
What is the rms current in the circuit?

A)0.11 A
B)0.13 A
C)0.14 A
D)0.17 A
E)0.20 A

Question 47

What rms current flows in a 60-mH inductor when 120-V rms ac at a frequency of 20 kHz is applied to it?

A)8.0 mA
B)16 mA
C)24 mA
D)32 mA

Question 48

A 120-V rms voltage at 1.0 kHz is applied to a 2.0-mH inductor,a 4.0-μF capacitor and a resistor.If the rms value of the current in this circuit is 0.40 A,what is the value of the resistor?

A)300 Ω
B)95 Ω
C)420 Ω
D)120 Ω
E)240 Ω

Question 49

A 120-V rms signal at 60 Hz is applied across a series combination of 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 50

As shown in the figure,an ac source whose rms voltage is 80 V is in series with a 100-Ω resistor and a capacitor whose reactance is 200 Ω at the frequency of the source.What is the rms voltage across the capacitor?

A)66 V
B)68 V
C)70 V
D)72 V
E)74 V

Question 51

A 120-V rms signal at 60.0 Hz is applied across a series combination of 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 resistance of the resistor?

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

Question 52

A 120-V rms voltage at 2000 Hz is applied to a 6.0-mH inductor,a 2.0-μF capacitor,and a 200-Ω resistor.What is the rms value of the current in this circuit?

A)1.5 A
B)0.48 A
C)2.5 A
D)3.5 A
E)0.59 A

Question 53

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

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

Question 54

The inductor in a radio receiver carries a current of amplitude 0.200 A when an ac voltage of amplitude 2.40 V is across it at a frequency of 1400 Hz.What is the value of the inductance?

A)1.43 mH
B)1.36 mH
C)9.20 mH
D)4.42 mH
E)1.97 mH

Question 55

What is the rms current through a 2.50-mH coil due to a 110-V rms,60-Hz source?

A)0.94 A
B)2.5 A
C)104 A
D)117 A

Question 56

A 120-V rms voltage at 1000 Hz is applied to an inductor,a 2.00-μF capacitor and a 100-Ω resistor.If the rms value of the current in this circuit is 0.680 A,what is the inductance of the inductor?

A)34.2 mH
B)35.8 mH
C)11.4 mH
D)17.9 mH
E)22.8 mH

Question 57

The figure shows a series ac circuit.The inductor has a reactance of 60 Ω and an inductance of 150 mH.A 50-Ω R and a capacitor C whose reactance is 90 Ω are also in the circuit,and the rms current in the circuit is 1.5 A.What is the rms voltage of the source?

A)87 V
B)84 V
C)81 V
D)78 V
E)75 V

Question 58

A 120-V rms signal at 60 Hz is applied across a series combination of a 30-mH inductor and a 100-Ω resistor.What is the rms value of the voltage across the resistor?

A)120 V
B)60 V
C)100 V
D)150 V
E)0.70 V

Question 59

A 120-V rms voltage is applied across a 6.0-μF capacitor and a series combination of a 100-Ω resistor.If the frequency of the power source 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 60

The figure shows a series ac circuit.The inductor has a reactance of 80 Ω and an inductance of 220 mH.A 30-Ω resistor and a capacitor whose reactance is 80 Ω are also in the circuit,and the rms current in the circuit is 2.0 A.What is the capacitance of the capacitor?

A)34 μF
B)37 μF
C)32 μF
D)30 μF
E)27 μF

Question 61

A series circuit has a 50-Hz ac source,a 40-Ω resistor,a 0.70-H inductor,and a 60-μF capacitor,as shown in the figure.The rms current in the circuit is 1.6 A.What is the voltage amplitude of the source?

A)390 V
B)330 V
C)270 V
D)220 V
E)190 V

Question 62

A series circuit has a 100-Ω resistor,a 0.100-μF capacitor,and a 2.00-mH inductor connected across a 120 V rms ac source operating at resonant frequency.What is the rms value of the voltage across the inductor?

A)170 V
B)150 V
C)120 V
D)54.0 V
E)533 V

Question 63

A series ac circuit has a resonance frequency of 9.0 kHz.If the inductor in the circuit has a value of 2.0 H,and the resistance is 75 Ω,what is the capacitance of the circuit?

A)0.16 pF
B)156 pF
C)6.2 pF
D)17.7 pF

Question 64

A resistance of 55 Ω,a capacitor of capacitive reactance 30 Ω,and an inductor of inductive reactance 30 Ω are connected in series to a 110-V rms,60-Hz power source.What rms current flows in this circuit?

A)2.0 A
B)less than 2.0 A
C)more than 2.0 A
D)none of the given answers

Question 65

An ac circuit has a 100-Ω resistor in series with a 4.9-μF capacitor and a 700-mH inductor.At what frequency does the circuit act like a pure resistance?

A)0.29 MHz
B)1.9 MHz
C)12 MHz
D)0.54 kHz
E)86 Hz

Question 66

A series RLC circuit has a 100-Ω resistor,a 0.100-μF capacitor and a 2.00-mH inductor connected across a 120-V rms ac voltage source operating at 1000/π Hz.What is the resonant frequency of this circuit?

A)70.7 kHz
B)17.9 kHz
C)22.5 kHz
D)35.3 kHz
E)11.3 kHz

Question 67

A series circuit has a 100-Ω resistor,a 0.100-μF capacitor,and a 2.00-mH inductor connected across a 120-V rms ac source operating at 1000/π Hz.What is the rms voltage across the inductor?

A)120 mV
B)87.1 mV
C)302 mV
D)96.1 mV
E)200 mV

Question 68

What is the resonance frequency of a series ac circuit consisting of a 40.0 μF capacitor,a 55-Ω resistor,and a 0.030 H inductor?

A)0.15 kHz
B)0.9 kHz
C)6.9 kHz
D)6 kHz

Question 69

A resistance of 55 Ω,a capacitor of capacitive reactance 30 Ω,and an inductor of inductive reactance 30 Ω are connected in series to a 110-V rms 60-Hz power source.What rms current flows in this circuit?

A)more than 4.0 A
B)2.0 A
C)more than 2.0 A but less than 4.0 A
D)4.0 A
E)less than 2.0 A

Question 70

What size capacitor should be placed in series with a 30-Ω resistor and a 40-mH inductive coil if the resonant frequency of the circuit is to be 1.0 kHz?

A)2.0 µF
B)0.63 µF
C)3.3 µF
D)6.0 µF
E)4.5 µF

Question 71

A series circuit consists of a 100-Ω resistor,a 10.0-μF capacitor,and a 0.350-H inductor.The circuit is connected to a 120-V rms,60-Hz power supply.What is the rms current in the circuit?

A)0.42 A
B)0.52 A
C)0.62 A
D)0.72 A

Question 72

A series circuit has a 100-Ω resistor,a 0.100-μF capacitor,and a 2.00-mH inductor connected across a 120-V rms ac source operating at resonant frequency.What is the rms value of the voltage across the capacitor?

A)54.0 V
B)120 V
C)150 V
D)533 V
E)170 V