Deck 21: Alternating-Current Circuits and Electromagnetic Waves

Question 1

An AC voltage source,with a peak output of 164 V,results in dissipation of energy in a resistor at rate of 139 W.What is the value of the resistance?

A) 193 Ω
B) 137 Ω
C) 48 Ω
D) 97 Ω
E) ​274 Ω

Answer 1

97 Ω

Question 2

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°

Answer 2

180°

Question 3

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.

Answer 3

back emf in the coil.

Question 4

When a 67-μF capacitor is attached to an AC source,its capacitive reactance is 97 Ω.If instead a 402-μF capacitor is attached to the same source,what will be its capacitive reactance?

A) 238 Ω
B) 39.6 Ω
C) 582 Ω
D) 16.2 Ω
E) ​2.57 Ω

Question 5

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 6

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 7

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 8

A 16.8-μF capacitor is connected to an AC source with an rms voltage of 155 V and a frequency of 85.0 Hz.What is the rms current in the capacitor?

A) 0.443 A
B) 0.695 A
C) 1.39 A
D) 0.98 A
E) ​1.97 A

Question 9

What is the impedance of an AC series circuit that is constructed of a 12.60-Ω resistor along with 18.97 Ω inductive reactance and 6.89 Ω capacitive reactance?

A) 38.5 Ω
B) 24.7 Ω
C) 21.7 Ω
D) 17.5 Ω
E) 5.82​ Ω

Question 10

In the inductor of a 74-Hz AC series circuit,the peak voltage precedes the peak current in each cycle by what time interval?

A) 14 × 10−³ s
B) 3.4 × 10−³ s
C) 6.8 × 10−³ s
D) 27 × 10−³ s
E) ​54 × 10−³ s

Question 11

What is the phase angle of an AC series circuit that is constructed of a 13.9-Ω resistor along with 19.06 Ω inductive reactance and 5.41 Ω capacitive reactance?

A) 44.5°
B) 34.5°
C) 52.8°
D) 44.8°
E) 50.5​°

Question 12

An AC voltage source,with a peak output of 206 V,is connected to a 74.0-Ω resistor.What is the rate of energy dissipated due to heat in the resistor?

A) 573 W
B) 287 W
C) 143 W
D) 405 W
E) ​183 W

Question 13

An AC voltage source,with a peak output of 309 V,is connected to a 80.0-Ω resistor.What is the effective (or rms)current in the circuit?

A) 2.73 A
B) 1.93 A
C) 3.86 A
D) 5.46 A
E) ​7.73 A

Question 14

In an AC series circuit the capacitive reactance is 389 Ω and frequency is 65 Hz.What is the capacitance?

A) 12.6 μF
B) 39.5 μF
C) 6.30 μF
D) 8.91 μF
E) ​17.8 μF

Question 15

What is the effective (rms)current value for an AC current with an amplitude of 14 A?

A) 14 A
B) 7.0 A
C) 9.9 A
D) 3.7 A
E) ​2.6 A

Question 16

In an AC series circuit the inductive reactance is 43.0 Ω and the frequency is 160 Hz.What is the inductance in the circuit?

A) 42.8 mH
B) 134 mH
C) 269 mH
D) 422 mH
E) ​207 mH

Question 17

In the typical household AC voltage of 119 V,what is the peak voltage?

A) 238 V
B) 168 V
C) 119 V
D) 84 V
E) ​60 V

Question 18

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 19

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

A) 1/3
B) 1/9
C) 3
D) 9
E) ​1

Question 20

The peak voltage of an AC source is 126 V.What is the rms voltage?

A) 63 V
B) 178 V
C) 89 V
D) 126 V
E) ​95 V

Question 21

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

A) 1/4.0
B) 1.0
C) 2.0
D) 4.0
E) ​0.5

Question 22

A resistor,inductor,and capacitor are connected in series,each with an effective (rms)voltage of 54 V,183 V,and 79 V,respectively.What is the magnitude of the phase angle in this circuit?

A) 27°
B) 68°
C) 60°
D) 63°
E) ​72°

Question 23

An AC series circuit has 10.02-Ω resistance,19.78-Ω inductive reactance,and 7.40-Ω capacitive reactance.If an effective (rms)emf of 111 V is applied,what is the power output?

A) 620 W
B) 230 W
C) 1210 W
D) 490 W
E) ​590 W

Question 24

A resistor,inductor,and capacitor are connected in series,each with effective (rms)voltage of 77 V,164 V,and 90 V,respectively.What is the value of the effective (rms)voltage of the applied source in the circuit?

A) 151 V
B) 107 V
C) 157 V
D) 331 V
E) ​202 V

Question 25

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 26

An AC series circuit has 11.9 Ω resistance,15.57 Ω inductive reactance and 7.29 Ω capacitive reactance.If an effective (rms)emf of 103 V is applied,what is the effective (rms)current value?

A) 5.66 A
B) 7.10 A
C) 0.49 A
D) 17.5 A
E) ​5.10 A

Question 27

The power factor in an AC series circuit is equal to which of the following ratios?

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

Question 28

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 29

A 48-Ω resistor,a 0.42-H inductor,and a 9.7-µF capacitor are connected in series to a 40-Hz source.The rms current in the circuit is 3.43 A.Find the rms voltage across the resistor,the inductor,and the capacitor.

A) 165 V,362 V,1407 V (all rms)
B) 165 V,362 V,236 V (all rms)
C) 1407V,58V,236V (all rms)
D) 517 V,58 V,1407 V (all rms)
E) ​517 V,362 V,236 V (all rms)

Question 30

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 31

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 32

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 62 V and 93 V (rms),respectively.What is the effective (rms)voltage of the source?

A) 155 V
B) 145 V
C) 112 V
D) 79 V
E) ​158 V

Question 33

In an RLC series circuit the capacitive reactance is 43.6 Ω.If the AC frequency doubles,what will be the resulting capacitive reactance?

A) 30.8 Ω
B) 21.8 Ω
C) 61.7 Ω
D) 87.2 Ω
E) ​Additional information is need to find the value.

Question 34

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 35

A 103-Ω resistor is connected in series with a 13.9-µF capacitor and a 88-Hz,225-V (rms)line voltage.If electrical energy costs 3.1¢ per kWh,how much does it cost to leave this circuit connected for 20 hours?

A) 5.0¢
B) 117.4¢
C) 1.22¢
D) 11.7¢
E) ​12.2¢

Question 36

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 37

What is the average power dissipation in a series RC circuit if R = 2.12 kΩ,C = 2.25 µF,and V = (267 V)cos 479t?

A) 14.1 W
B) 33.6 W
C) 16.8 W
D) 20.0 W
E) ​39.9 W

Question 38

A resistor,inductor and capacitor are connected in series,each with effective (rms)voltage of 69 V,184 V and 58 V,respectively.If the resistor is rated at 31 Ω,what is the average power dissipated in the circuit?

A) 666 W
B) 154 W
C) 74 W
D) 320 W
E) ​584 W

Question 39

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

A) 1/3.0
B) 1.00
C) 1.7
D) 3.0
E) ​9.0

Question 40

In an RLC series circuit the phase angle between the current and voltages is 30°.If the AC frequency doubles,what is the resulting phase angle?

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

Question 41

An AM radio tuning circuit has a coil with an inductance of 1.65 mH and a capacitor set at 7.01 × 10−⁶ μF.What frequency will it detect?

A) 1236 kHz
B) 1480 kHz
C) 2470 kHz
D) 236 kHz
E) ​740 kHz

Question 42

An FM radio tuning circuit has a coil with an inductance of 0.0021 mH.What is the value of the capacitance if the set is tuned to 102.7 MHz?

A) 4.6 × 10−⁶ μF
B) 3.6 × 10−⁶ μF
C) 7.4 × 10−⁶ μF
D) 1.14 × 10−⁶ μF
E) ​11.3 × 10−⁶ μF

Question 43

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 44

The primary winding of an electric train transformer has 235 turns,and the secondary has 72.If the input voltage is 191 V(rms),what is the output voltage?

A) 623 V
B) 18 V
C) 59 V
D) 345 V
E) ​191 V

Question 45

A series RLC circuit in a radio is in resonance with AM 500 kHz.If the radio station is changed to AM 1500 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 46

A transformer is to be designed to increase the 41-kV (rms)output of a generator to the transmission line voltage of 388 kV (rms).If the primary winding has 98 turns,how many turns must the secondary have?

A) 10
B) 8776
C) 927
D) 31
E) ​2852

Question 47

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 48

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 49

What is the average power dissipation in an RLC series circuit in which R = 140 Ω,L = 0.38 H,and C = 10 µF driven at resonance by a 102-V (rms)source?

A) 70 W
B) 9 W
C) 15 W
D) 26 W
E) ​92 W

Question 50

A transformer consists of a 705-turn primary coil and a 2757-turn secondary coil.If the current in the secondary is 1.11 A,what is the primary current?

A) 0.28 A
B) 2.20 A
C) 4.34 A
D) 1.11 A
E) ​0.56 A

Question 51

An AC series circuit contains a resistor of 10 Ω,a capacitor of 1.20 μF and an inductor of 110 mH.What frequency should be used to create a resonance condition in the circuit?

A) 139 Hz
B) 1210 Hz
C) 1100 Hz
D) 438 Hz
E) ​877 Hz

Question 52

A series RLC AC circuit is at resonance.It contains a resistor of 23 Ω,a capacitor of 0.25 μF and an inductor of 119 mH.If an effective (rms)voltage of 177 V is applied,what is the effective (rms)current when the circuit is in resonance?

A) 4.2 A
B) 7.7 A
C) 14 A
D) 2.6 A
E) ​28 A

Question 53

An AC power generator produces 60.64 A (rms)at 2195 V.The voltage is stepped up to 104,222 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) 2879 A
B) 1.28 A
C) 60.64 A
D) 8.80 A
E) ​417.9 A

Question 54

Find the resonant frequency for a series RLC circuit where R = 21 Ω,C = 8.4 µF,and L = 2.80 mH.

A) 3260 Hz
B) 1038 Hz
C) 1470 kHz
D) 677 kHz
E) ​650 kHz

Question 55

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

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

Question 56

An AC power generator produces 14 A (rms)at 2103 V.The energy is transmitted through a long-distance power line,which has a total resistance of 145 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) 3%
B) 19%
C) 31%
D) 97%
E) ​93%

Question 57

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 58

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 59

A series RLC circuit has a inductive reactance of 2 Ω and a capacitive reactance of 1/2 Ω.By what factor should the AC frequency be changed to put this circuit into resonance?

A) 2
B) 1/2
C) 1/1.41
D) 1.41
E) This circuit cannot be made to achieve resonance.

Question 60

An AC series circuit contains a resistor of 16 Ω,an inductor of 43 mH and a variable capacitor.If the frequency of the applied voltage is 310 Hz,to what setting should the capacitor be set if resonance is achieved?

A) 60.5 µF
B) 24.5 µF
C) 11.9 µF
D) 6.1 µF
E) ​49.1 µF

Question 61

In order to keep its food hot,a restaurant will place it under which type of lamp?

A) infrared
B) visible light
C) ultraviolet
D) x-ray

Question 62

Determine the amount of energy carried in 1.1 m of a 4.2-mW He-Ne laser beam if the cross-sectional area of the beam is 2.6 × 10−⁶ m².

A) 6.5E-11 J
B) 2.5E-12 J
C) 1.5E-11 J
D) 1.7E-8 J
E) ​5.1E-12 J

Question 63

The Earth is 1.49 × 10¹¹ m from the Sun.If the solar radiation at the top of the Earth's atmosphere is 1 340 W/m²,what is the total power output of the Sun?

A) 7.48 × 10²⁷ W
B) 2.34 × 10³⁰ W
C) 6.62 × 10²⁶ W
D) 3.74 × 10²⁶ W

Question 64

A radar pulse sent out to an airplane at a distance of 24.1 km will return as an echo to the source in what time interval? (c = 3.00 × 10⁸ m/s)

A) 33.3 × 10−⁶ s
B) 80 × 10−⁶ s
C) 161 × 10−⁶ s
D) 40.2 × 10−⁶ s
E) ​482 × 10−⁶ s

Question 65

In order of increasing frequency,which of the following is correct?

A) visible,radio,ultraviolet and x-ray
B) infrared,visible,ultraviolet and gamma
C) visible,gamma,ultraviolet and x-ray
D) infrared,x-ray,visible and gamma

Question 66

A radar pulse returns 2.1 × 10−⁴ seconds after it is sent out,having been reflected by an object.What is the distance between the radar antenna and the object? (c = 3.00 × 10⁸ m/s)

A) 6.3E+4 m
B) 9.9E+4 m
C) 3.2E+4 m
D) 1.1E+4 m
E) ​1.8E+4 m

Question 67

What is the maximum value of the electric field E at 0.9 m from a 55-W light bulb radiating in all directions? (µ₀ = 4π × 10−⁷ T⋅m/A,c = 3.00 × 10⁸ m/s)

A) 64 V/m
B) 3700 V/m
C) 4100 V/m
D) 800 V/m
E) ​290 V/m

Question 68

A solar cell has a light-gathering area of 12 cm² and produces 0.33 A at 0.67 V (dc)when illuminated with sunlight of intensity 858 W/m².What is the efficiency of the solar cell?

A) 21%
B) 1.8%
C) 31%
D) 2%
E) ​47%

Question 69

An electromagnetic wave with a peak electric field component of 1.74 × 10² N/C has what associated peak magnetic field value? (ε₀ = 8.85 × 10−¹² C²/N⋅m²,μ₀ = 4π × 10−⁷ T⋅m/A and c = 3.00 × 10⁸ m/s)

A) 5.22E+10 T
B) 1.72E+6 T
C) 5.80E-7 T
D) 7.29E-13 T
E) ​1.15E+4 T

Question 70

Peak values for a neodymium-glass laser are 600 J for 1.0 nanosecond.If the cross-section of the laser beam is 1.64 cm²,what are the maximum values of E and B? (µ₀ = 4π × 10−⁷ T⋅m/A,c = 3.00 × 10⁸ m/s)

A) 1.7E+9 V/m,1.6 T
B) 4.7E+8 V/m,5.5 T
C) 1.7E+9 V/m,5.5 T
D) 4.7E+8 V/m,1.6 T
E) ​Not enough information.

Question 71

A radio wave signal,which transmits at a frequency of 5.77 MHz,has what wavelength? (c = 3.00 × 10⁸ m/s)

A) 520 m
B) 104 m
C) 52.0 m
D) 163 m
E) ​27.0 m

Question 72

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

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

Question 73

An electromagnetic wave with a peak magnetic field component of 1.68 × 10−⁷ T has an associated peak electric field component of what value? (μ₀ = 4π × 10−⁷ T⋅m/A,ε₀ = 8.85 × 10−¹² C²/N⋅m² and c = 3.00 × 10⁸ m/s)

A) 1.98E-2 N/C
B) 5.60E-9 N/C
C) 50.4 N/C
D) 1.79E+8 N/C
E) ​6.33E-6 N/C

Question 74

If the radiant energy from the Sun comes in as a plane EM wave of intensity 1 340 W/m²,calculate the peak values of E and B.(µ₀ = 4π × 10−⁷ T⋅m/A,c = 3.00×10⁸ m/s)

A) 330 V/m,3.0 × 10−⁴ T
B) 1 010 V/m,3.35 × 10−⁶ T
C) 330 V/m,3.35 × 10−⁶ T
D) 1 010 V/m,3.0 × 10−⁴ T

Question 75

A radio wave transmits 2.99 W/m² average power per unit area.What is the peak value of the associated magnetic field? (μ₀ = 4π × 10−⁷ T⋅m/A and c = 3.00 × 10⁸ m/s)

A) 2.50E-14 T
B) 4.75E+1 T
C) 1.58E-7 T
D) 9.98E-5 T
E) ​1.12E-7 T

Question 76

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 77

Glass panes are opaque to a certain type of radiation,which passes through quartz.What type of radiation is it? This radiation is important in ozone layer reactions.

A) microwave
B) gamma
C) x-ray
D) ultraviolet

Question 78

An electromagnetic wave is made up of which of the following oscillating quantities?

A) electrons only
B) electric fields only
C) magnetic fields only
D) electric and magnetic fields

Question 79

An electromagnetic wave with a peak magnetic field component of 1.06 × 10−⁷ T carries what average power per unit area? (μ₀ = 4π × 10−⁷ T⋅m/A,ε₀ = 8.85 × 10−¹² C²/N⋅m² and c = 3.00 × 10⁸ m/s)

A) 4.21 W/m²
B) 2.68 W/m²
C) 1.34 W/m²
D) 1.27 W/m²
E) ​2.53 W/m²

Question 80

Which condition of motion must be met with regard to a charged particle if it is in the process of emitting electromagnetic radiation?

A) moves at constant velocity
B) accelerates
C) moves at the speed of light
D) moves parallel to a uniform magnetic field