Deck 21: Alternating-Current Circuits and Electromagnetic Waves

Question 1

What is the effective (rms)current value for an AC current with an amplitude of 15.4 A?

A)15.4 A
B)7.70 A
C)10.9 A
D)3.92 A
E)2.77 A

Answer 1

10.9 A

Question 2

When a 47-μF capacitor is attached to an AC source,its capacitive reactance is 42.0 Ω.If instead a 150-μF capacitor is attached to the same source,what will be its capacitive reactance?

A)75 Ω
B)23 Ω
C)130 Ω
D)13 Ω
E)2.1 Ω

Answer 2

13 Ω

Question 3

An AC voltage source,with a peak output of 114 V,is connected to a 40.0-Ω resistor.What is the effective (or rms)current in the circuit?

A)2.02 A
B)1.43 A
C)2.85 A
D)4.03 A
E)5.70 A

Answer 3

2.02 A

Question 4

In a capacitor in an AC circuit,the voltage:

A)leads the current by 90°.
B)lags the current by 90°.
C)may lead or lag the current depending on the frequency.
D)is in phase with 70.7% of the current.

Question 5

The frequency in an AC series circuit is quadrupled.By what factor does this change the capacitive reactance?

A)1/4
B)1/16
C)4
D)16
E)​1

Question 6

A 400-Ω resistor and a capacitor are connected in parallel across a 300-Hz source.If the amplitude of the current in the resistor is equal to that in the capacitor,what is the value of the capacitance?

A)1.33 μF
B)0.750 μF
C)10.6 μF
D)0.212 F

Question 7

The rms current is equal to the direct current that:

A)produces the same average voltage across a resistor as in an AC circuit.
B)dissipates an equal amount of energy in a resistor at the same rate as in an AC circuit.
C)provides the same average current in a resistor as in an AC circuit.
D)results in the same peak power in a resistor as in an AC circuit.

Question 8

The current in an inductor connected to an AC voltage source lags the voltage.This lag is caused by the:

A)back emf in the coil.
B)voltage across the coil.
C)time required for electrical signals to travel through all the coils of an inductance.
D)resistance of the coil.

Question 9

In an AC series circuit,the current in a pure resistor differs in phase with the applied voltage by what angle?

A)zero
B)45°
C)90°
D)180°

Question 10

An AC voltage source,with a peak output of 72 V,results in dissipation of energy in a resistor at rate of 140 W.What is the value of the resistance?

A)37 Ω
B)26 Ω
C)9 Ω
D)19 Ω
E)52 Ω

Question 11

In the inductor of a 59-Hz AC series circuit,the peak voltage precedes the peak current in each cycle by what time interval?

A)1.7E-2 s
B)4.2E-3 s
C)8.5E-3 s
D)3.4E-2 s
E)6.8E-2 s

Question 12

In the typical household AC voltage of 311 V,what is the peak voltage?

A)622 V
B)440 V
C)311 V
D)220 V
E)156 V

Question 13

The peak voltage of an AC source is 296 V.What is the rms voltage?

A)148 V
B)419 V
C)209 V
D)296 V
E)222 V

Question 14

The rate of heat dissipation in an AC circuit with resistance,R,and effective current,I_rms,is given by which of the following?

A)0.5 × (I_rms)²R
B)(I_rms)²R
C)2.0 × (I_rms)²R
D)4.0 × (I_rms)²R

Question 15

An AC voltage source,with a peak output of 122 V,is connected to a 54.0-Ω resistor.What is the rate of energy dissipated due to heat in the resistor?

A)276 W
B)138 W
C)68.9 W
D)195 W
E)87.7 W

Question 16

In an AC circuit operating at a frequency where the phase angle with respect to the current is 30°,what happens to the phase angle if the capacitance of the circuit is increased?

A)It increases.
B)It decreases.
C)nothing
D)It decreases and can become zero.

Question 17

The peak voltage of an AC source is 400 V.What is the rms voltage?

A)100 V
B)200 V
C)141 V
D)283 V

Question 18

In an AC series circuit the capacitive reactance is 217 Ω and frequency is 56 Hz.What is the capacitance?

A)2.62E-5 F
B)8.23E-5 F
C)1.31E-5 F
D)1.85E-5 F
E)3.71E-5 F

Question 19

In an AC series circuit the inductive reactance is 41.0 Ω and the frequency is 137 Hz.What is the inductance in the circuit?

A)4.8E-2 H
B)1.5E-1 H
C)3.0E-1 H
D)4.7E-1 H
E)2.2E-1 H

Question 20

A 13.7-μF capacitor is connected to an AC source with an rms voltage of 148 V and a frequency of 40.0 Hz.What is the rms current in the capacitor?

A)0.162 A
B)0.255 A
C)0.509 A
D)0.360 A
E)0.720 A

Question 21

In an RL circuit,which of the following is a possible magnitude of a phase angle?

A)45^°
B)315^°
C)225^°
D)135^°

Question 22

In an RLC series circuit the capacitive reactance is 19.5 Ω.If the AC frequency triples,what will be the resulting capacitive reactance?

A)11.3 Ω
B)6.5 Ω
C)33.8 Ω
D)58.5 Ω
E)Additional information is need to find the value.

Question 23

A resistor,inductor,and capacitor are connected in series,each with effective (rms)voltage of 64.0 V,87.6 V,and 69.0 V,respectively.What is the value of the effective (rms)voltage of the applied source in the circuit?

A)82.6 V
B)66.6 V
C)83.7 V
D)220.6 V
E)129 V

Question 24

In an AC series circuit,the voltage in the inductor differs in phase with the voltage in the capacitor by what angle?

A)zero
B)45°
C)90°
D)180°

Question 25

A resistor and capacitor are connected in series with an applied AC voltage source.Separate voltmeter readings across the resistor and capacitor give values of 23 V and 29 V (rms),respectively.What is the effective (rms)voltage of the source?

A)7.2 V
B)47 V
C)37 V
D)26 V
E)18 V

Question 26

An AC circuit consists of a 60-Hz source,a 200-Ω resistor,and a 1.06-H inductor,all in series.What is the impedance of this circuit?

A)400 Ω
B)280 Ω
C)600 Ω
D)450 Ω

Question 27

In an RLC series circuit,if the AC frequency is decreased to a very small value,what value does the phase angle between the current and voltage approach?

A)90°
B)0°
C)-90°
D)45°

Question 28

Consider an AC series circuit containing a coil,capacitor and resistance.Tripling the frequency will change the circuit's impedance by what factor?

A)1/3
B)1.0
C)3
D)Information is insufficient to determine answer.

Question 29

A series circuit has equal values for resistance,capacitive reactance,and inductive reactance.The phase angle for this circuit is:

A)60°.
B)-60°.
C)180°.
D)not given.

Question 30

In an RLC circuit,the maximum current is 1 amp.What is the average current?

A) A
B) A
C)(1/2)A
D)None of the above.

Question 31

What is the impedance of an AC series circuit that is constructed of a 10.0-Ω resistor along with 24.0-Ω inductive reactance and 7.0-Ω capacitive reactance?

A)19.7 Ω
B)11.2 Ω
C)41.0 Ω
D)27.7 Ω

Question 32

In an RLC series circuit,if the AC frequency is increased to a very large value,what value does the phase angle between the current and voltage approach?

A)90°
B)0°
C)-90°
D)45°

Question 33

An AC series circuit has 16.5 Ω resistance,12.8 Ω inductive reactance and 8.27 Ω capacitive reactance.If an effective (rms)emf of 145 V is applied,what is the effective (rms)current value?

A)7.56 A
B)8.47 A
C)0.495 A
D)23.7 A
E)6.89 A

Question 34

What is the phase angle of an AC series circuit that is constructed of a 14.5-Ω resistor along with 16.5-Ω inductive reactance and 9.41-Ω capacitive reactance?

A)26.1°
B)11.9°
C)43.1°
D)35.0°
E)38.7°

Question 35

Consider an AC series circuit containing a coil,capacitor and resistance.Doubling the frequency will change the inductive reactance by what factor?

A)1/2
B)1
C)
D)2
E)1/2.

Question 36

Consider an AC series circuit containing a coil,capacitor,and resistance.Doubling the frequency will change the capacitive reactance by what factor?

A)1/2
B)1
C)
D)2
E)2²

Question 37

In an AC circuit,the ratio of average current to maximum current is:

A)zero.
B)0.5.
C)0.707.
D)1.0.

Question 38

An RLC circuit is connected across an AC power source.How are the maximum and rms voltages from the power source related?​

A)​Δ​V​_max = ΔV​_rms
B)​Δ​V​_max = ΔV​_rms/
C)​Δ​V​_max = 2ΔV​_rms
D)​Δ​V​max = ΔV​rms/2

Question 39

A 400-Ω resistor and an inductor are connected in parallel across a 300-Hz source.If the amplitude of the current in the resistor is equal to that in the inductor,what is the value of the inductance?

A)0.212 H
B)0.666 H
C)1.33 × 10^-6 H
D)0.333 H

Question 40

What is the impedance of an AC series circuit that is constructed of a 12.5-Ω resistor along with 13.6-Ω inductive reactance and 3.43-Ω capacitive reactance?

A)29.5 Ω
B)22.7 Ω
C)18.2 Ω
D)16.1 Ω
E)3.36 Ω

Question 41

A 104-Ω resistor is connected in series with a 14.7-µF capacitor and a 56-Hz,136-V (rms)line voltage.If electrical energy costs 4.8¢ per kWh,about how much does it cost to leave this circuit connected for 24 hours?

A)2¢
B)46¢
C)200¢
D)5¢

Question 42

The power dissipated in an AC series circuit increases as the phase angle approaches what value?

A)zero
B)45°
C)90°
D)180°

Question 43

An electric motor produces 2.0 hp in a V_rms = 120 V circuit.Using 1 hp = 746 W,how long would it take this motor to do 1.0 kWh of work?

A)0.67 min
B)0.67 h
C)1.3 min
D)1.3 h

Question 44

​A series RLC circuit is connected across a 240-Hz AC source,where ΔV_max = 140 V,R = 480 Ω,C = 0.250 μF,and L = 3.25 H.What is the average power delivered to this circuit?

A)​77.9 W
B)​1.78 W
C)​3.56 W
D)​0.890 W

Question 45

​A circuit consists of an AC audio amplifier,a resistor,and a speaker,all in series.The amplifier puts out an alternating voltage of 16.0 V (rms),the resistance of the resistor is 10.0 Ω,and the speaker has a resistance of 11.9 Ω.What is the time-averaged power delivered to the speaker?

A)​21.5 W
B)​30.5 W
C)​6.35 W
D)​8.69 W

Question 46

What is the average power dissipation in an RLC series circuit in which R = 177 Ω,L = 0.060 H,and C = 8.65 µF driven at resonance by a 163-V (rms)source?

A)150 W
B)138 W
C)147 W
D)144 W
E)1 370 W

Question 47

What is the average power dissipation in a series RC circuit if R = 6.35 kΩ,C = 2.64 µF,and V = (192 V)cos 115t?

A)2.29 W
B)5.81 W
C)2.90 W
D)3.23 W
E)6.47 W

Question 48

An AM radio tuning circuit has a coil with an inductance of 3.93 mH and a capacitor set at 5.68 × 10−¹² F.What frequency will it detect?

A)8.90E+5 Hz
B)1.07E+6 Hz
C)1.78E+6 Hz
D)1.70E+5 Hz
E)5.33E+5 Hz

Question 49

An AC series circuit contains a resistor of 30.0 Ω,a capacitor of 1.22 μF and an inductor of 154 mH.What frequency should be used to create a resonance condition in the circuit?

A)3.49E+2 Hz
B)8.48E+2 Hz
C)9.21E+2 Hz
D)3.67E+2 Hz
E)7.35E+2 Hz

Question 50

A resistor,inductor and capacitor are connected in series,each with effective (rms)voltage of 80.0 V,160 V,and 84.0 V,respectively.If the resistor is rated at 15.0 Ω,what is the average power dissipated in the circuit?

A)812 W
B)427 W
C)309 W
D)589 W
E)559 W

Question 51

A series RLC AC circuit is at resonance.It contains a resistor of 18.7 Ω,a capacitor of 0.460 μF and an inductor of 70.9 mH.If an effective (rms)voltage of 41.0 V is applied,what is the effective (rms)current when the circuit is in resonance?

A)1.25 A
B)2.19 A
C)3.84 A
D)0.672 A
E)7.68 A

Question 52

An AC series circuit has 18.9-Ω resistance,21.1-Ω inductive reactance,and 15.5-Ω capacitive reactance.If an effective (rms)emf of 94 V is applied,what is the power output?

A)2.34E+2 W
B)1.60E+2 W
C)4.66E+2 W
D)4.30E+2 W
E)2.32E+2 W

Question 53

Find the resonant frequency for a series RLC circuit where R = 18.0 Ω,C = 9.7 µF,and L = 8.30 mH.

A)1.76E+3 Hz
B)5.61E+2 Hz
C)7.93E+2 Hz
D)1.98E+3 Hz
E)3.51E+2 Hz

Question 54

A series RLC circuit in a radio is in resonance with AM 700 kHz.If the radio station is changed to AM 2100 kHz,by what factor must the capacitance be multiplied to again achieve resonance?

A)​9
B)3
C)1
D)1/3
E)​1/9

Question 55

A resistor,inductor,and capacitor are connected in series,each with an effective (rms)voltage of 63 V,176 V,and 65 V,respectively.What is the magnitude of the phase angle in this circuit?

A)30°
B)64°
C)59°
D)60°
E)69°

Question 56

A 58-Ω resistor,a 0.40-H inductor,and a 10.0-µF capacitor are connected in series to a 106-Hz source.The rms current in the circuit is 3.99 A.Find the rms voltage across the resistor,the inductor,and the capacitor.

A)231 V,1063 V,599 V (all rms)
B)231 V,1063 V,154 V (all rms)
C)599 V,169 V,154 V (all rms)
D)727 V,169 V,599 V (all rms)
E)727 V,1063 V,154 V (all rms)

Question 57

In an LCR series circuit with X_L > X_C,the phase angle between the current and voltage phasors is 30°.If the AC frequency doubles,what is the magnitude of the resulting phase angle?

A)30°
B)less than 30°
C)more than 30°
D)Additional information is needed to reach a determination.

Question 58

An electric motor produces 2.0 hp in a V_rms = 120 V circuit.What is I_rms for this motor? (1 hp = 746 W)

A)12 A
B)6.2 A
C)0.62 A
D)1.6 A

Question 59

An FM radio tuning circuit has a coil with an inductance of 0.0036 mH.What is the value of the capacitance if the set is tuned to 91.3 MHz?

A)3.38E-12 F
B)2.65E-12 F
C)4.84E-13 F
D)8.45E-13 F
E)8.33E-12 F

Question 60

An AC series circuit contains a resistor of 20.0 Ω,an inductor of 74.0 mH and a variable capacitor.If the frequency of the applied voltage is 423 Hz,to what setting should the capacitor be set if resonance is achieved?

A)1.89E-5 F
B)7.66E-6 F
C)5.09E-6 F
D)1.91E-6 F
E)1.91E-5 F

Question 61

Which of the following combinations of circuit components can be used to make a tuner for a radio,to select the desired frequency?

A)fixed inductor,variable resistor
B)fixed resistor,variable inductor
C)fixed inductor,variable capacitor
D)fixed capacitor,variable resistor

Question 62

An AC power generator produces 42.9 A (rms)at 2 970 V.The voltage is stepped up to 6 000 V by an ideal transformer,and the energy transmitted through a long-distance power line with a total resistance of 100 Ω.What is the rms current in the long-distance line?

A)87 A
B)21.2 A
C)42.9 A
D)30.2 A
E)61.0 A

Question 63

Which one of the following scientists made the theoretical prediction that electromagnetic waves travel through a vacuum at the speed of light?

A)Hertz
B)Faraday
C)Maxwell
D)Lenz

Question 64

An RLC circuit is connected across an AC power source.Which statement is correct?​

A)​The voltage across the inductor lags the current by 90°.
B)​ The voltage across the capacitor is in phase with the current.
C)​At resonance,the phase angle $\phi$ between the current and the voltage is 0.
D)​None of the above statements are correct.

Question 65

At what frequency does a 0.32-H inductor have the same reactance as a 0.22-μF capacitor?

A)3.8 × 10³ Hz
B)3.6 × 10⁵ Hz
C)24 Hz
D)6.0 × 10² Hz

Question 66

Resonance occurs in an AC series circuit when which of the following conditions is met?

A)resistance equals capacitive reactance
B)resistance equals inductive reactance
C)capacitive reactance equals inductive reactance
D)capacitive reactance equals zero

Question 67

Maxwell developed his theory of electromagnetism by combining previous discoveries.He added his own original hypothesis that:

A)electric charges produce electric fields.
B)moving electric charges produce magnetic fields.
C)changing electric fields produce magnetic fields.
D)changing magnetic fields produce electric fields.

Question 68

Transmitting power at high voltage, e.g., 400,000 V, reduces the power loss for transmission lines. But such a voltage would destroy electrical devices in household use. How then can such 400,000 V electricity be used in a normal house?

A) The ground prongs on household plugs reduce the voltage to 120 V.
B) Before reaching households, transformers are used to reduce the voltage appropriately.
C) No matter the incoming voltage, a 120-V device only lets 120 V in.
D) The 400,000 V is just theoretical; long distance transmission lines actually use 120 V.

Question 69

Maxwell guessed that visible light was an electromagnetic wave because of its:

A)frequency.
B)wavelength.
C)speed.
D)energy.

Question 70

The primary winding of an electric train transformer has 445 turns,and the secondary has 300.If the input voltage is 118 V(rms),what is the output voltage?

A)175 V
B)53.6 V
C)79.6 V
D)144 V
E)118 V

Question 71

An engineer designed a transformer to convert 120 V (rms) to 6.0 V (rms). The number of turns in the primary is 540, and the secondary current is 610 mA at an output voltage of 6.0 V (rms).
How many turns are in the secondary?

A)90
B)27
C)5
D)3 240

Question 72

A transformer is to be designed to increase the 27-kV (rms)output of a generator to the transmission line voltage of 346 kV (rms).If the primary winding has 95 turns,how many turns must the secondary have?

A)7
B)15600
C)1217
D)26
E)4358

Question 73

An ideal transformer is one that:

A)has a turn ratio,N₂/N₁,equal to 1.
B)works with direct current.
C)experiences no power loss.
D)has an output frequency of 60 Hz.

Question 74

Which one of the following scientists first built and operated devices that could emit and detect human-made electromagnetic radiation?

A)Hertz
B)Ampere
C)Maxwell
D)Lenz

Question 75

When an RLC series circuit is in resonance,its impedance is:

A)zero.
B)equal to its resistance.
C)a maximum.
D)π/2 Ω.

Question 76

A transformer consists of a 780-turn primary coil and a 1 403-turn secondary coil.If the current in the secondary is 3.49 A,what is the primary current?

A)1.94 A
B)4.68 A
C)6.28 A
D)3.49 A
E)2.60 A

Question 77

An LCR circuit has resistance R₀,inductance L₀,and capacitance C₀.If the resistance value is now tripled,which values of inductance and capacitance will result in the same resonant frequency as before?

A)3L₀,C₀
B)L₀/3,C₀/3
C)3L₀,3C₀
D)3L₀,C₀/3

Question 78

A series RLC circuit has an inductive reactance of 5 Ω and a capacitive reactance of 1/5 Ω.By what factor should the AC frequency be changed to put this circuit into resonance?

A)5
B)1/5
C)1/
D)
E)This circuit cannot be made to achieve resonance.

Question 79

An AC power generator produces 27 A (rms)at 4730 V.The energy is transmitted through a long-distance power line,which has a total resistance of 173 Ω.What percentage of the power delivered by the generator is dissipated as heat in the long-distance line if a step-up transformer is not used?

A)1%
B)20%
C)31%
D)99%
E)​98%

Question 80

An engineer designed a transformer to convert 120 V (rms) to 6.0 V (rms). The number of turns in the primary is 540, and the secondary current is 610 mA at an output voltage of 6.0 V (rms).
​What is the current in the primary?

A)​30.5 mA
B)​4.50 mA
C)​32.8 mA
D)​136 mA