Deck 21: Alternating Current Circuits and Electromagnetic Waves

Question 1

In an AC series circuit the inductive reactance is 50 W and the frequency is 100 Hz.What is the inductance in the circuit?

A)80 mH
B)240 mH
C)500 mH
D)740 mH

Answer 1

80 mH

Question 2

In a capacitor in an AC circuit, the voltage:

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

Answer 2

lags the current by 90 $\degree$ .

Question 3

In an AC series circuit the capacitive reactance is 200 W and frequency is 100 Hz.What is the capacitance?

A)3.2 mF
B)6.28 mF
C)8.0 mF
D)50.0 mF

Answer 3

8.0 mF

Question 4

What is the effective (rms) current value for an AC current with an amplitude of 10 A?

A)28 A
B)3.1 A
C)7.1 A
D)14 A

Question 5

An AC voltage source, with a peak output of 200 V, is connected to a 50-W resistor.What is the rate of energy dissipated due to heat in the resistor?

A)200 W
B)400 W
C)566 W
D)800 W

Question 6

In the typical household AC voltage of 120 V, what is the peak voltage?

A)240 V
B)170 V
C)120 V
D)85 V

Question 7

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 8

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 $\degree$
C)90 $\degree$
D)180 $\degree$

Question 9

What is the phase angle of an AC series circuit that is constructed of a 10.0-W resistor along with 12.00 W inductive reactance and 7.00 W capacitive reactance?

A)26.6 $\degree$
B)18.4 $\degree$
C)87.0 $\degree$
D)63.4 $\degree$

Question 10

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 $\degree$
C)90 $\degree$
D)180 $\degree$

Question 11

In the inductor of a 60-Hz AC series circuit, the peak voltage precedes the peak current in each cycle by what time interval?

A)2.1 * 10^-3 s
B)4.2 * 10^-3 s
C)8.3 * 10^-3 s
D)1.7 * 10^-3 s

Question 12

An AC voltage source, with a peak output of 120 V, results in dissipation of energy in a resistor at rate of 100 W.What is the value of the resistance?

A)144 W
B)120 W
C)100 W
D)72 W

Question 13

An AC voltage source, with a peak output of 200 V, is connected to a 50-W resistor.What is the effective (or rms) current in the circuit?

A)2.8 A
B)4.0 A
C)5.6 A
D)2.0 A

Question 14

A 12.0-mF capacitor is connected to an AC source with an rms voltage of 120 V and a frequency of 60.0 Hz.What is the rms current in the capacitor?

A)1.41 A
B)0.768 A
C)0.543 A
D)0 A

Question 15

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 16

When a 50-mF capacitor is attached to an AC source, its capacitive reactance is 40 W.If instead a 100-mF capacitor is attached to the same source, what will be its capacitive reactance?

A)80 O
B)57 O
C)28 O
D)20 O

Question 17

What is the impedance of an AC series circuit that is constructed of a 10.0-W resistor along with 12.0 W inductive reactance and 7.0 W capacitive reactance?

A)37.0 W
B)27.7 W
C)27.1 W
D)11.2 W

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 doubled.By what factor does this change the capacitive reactance?

A)1/2
B)1/4
C)2
D)4

Question 20

The peak voltage of an AC source is 200 V.What is the rms voltage?

A)282 V
B)200 V
C)141 V
D)100 V

Question 21

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
B)1.0
C)1.73
D)3.0

Question 22

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

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

Question 23

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 50 V and 75 V (rms), respectively.What is the effective (rms) voltage of the source?

A)25 V
B)63 V
C)90 V
D)125 V

Question 24

A resistor, inductor, and capacitor are connected in series, each with an effective (rms) voltage of 65 V, 140 V, and 80 V, respectively.What is the magnitude of the phase angle in this circuit?

A)22 $\degree$
B)28 $\degree$
C)37 $\degree$
D)43 $\degree$

Question 25

An AC series circuit has 12.0 W resistance, 15.00 W inductive reactance and 10.00 W capacitive reactance.If an effective (rms) emf of 120 V is applied, what is the power output?

A)1 540 W
B)1 300 W
C)1 160 W
D)1 020 W

Question 26

An AC series circuit has 12.0 W resistance, 15.00 W inductive reactance and 10.00 W capacitive reactance.If an effective (rms) emf of 120 V is applied, what is the effective (rms) current value?

A)5.31 A
B)9.23 A
C)10.8 A
D)26.0 A

Question 27

What is the average power dissipation in a series RC circuit if R = 5.00 kW, C = 2.00 µF, and V = (170 V) cos 300t?

A)2.60 W
B)2.74 W
C)28.2 W
D)157 W

Question 28

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 29

A resistor, inductor and capacitor are connected in series, each with effective (rms) voltage of 65 V, 140 V and 80 V, respectively.If the resistor is rated at 24 W, what is the average power dissipated in the circuit?

A)88 W
B)176 W
C)238 W
D)323 W

Question 30

A resistor, inductor, and capacitor are connected in series, each with effective (rms) voltage of 65 V, 140 V, and 80 V, respectively.What is the value of the effective (rms) voltage of the applied source in the circuit?

A)48 V
B)88 V
C)95 V
D)285 V

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 $\degree$
B)0 $\degree$
C)-90 $\degree$
D)45 $\degree$

Question 32

In an RLC series circuit the capacitive reactance is 24 W.If the AC frequency doubles, what will be the resulting capacitive reactance?

A)24 W
B)12 W
C)48 W
D)Additional information is need to find the value.

Question 33

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

A)60 $\degree$ .
B)-60 $\degree$ .
C)180 $\degree$ .
D)not given.

Question 34

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 35

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)3.0
D)Information is insufficient to determine answer.

Question 36

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

A)zero
B)45 $\degree$
C)90 $\degree$
D)180 $\degree$

Question 37

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 38

A 200-W resistor is connected in series with a 10-µF capacitor and a 60-Hz, 120-V (rms) line voltage.If electrical energy costs 5.0¢ per kWh, how much does it cost to leave this circuit connected for 24 hours?

A)62¢
B)31¢
C)5.2¢
D)3.1¢

Question 39

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

A)1/3
B)1.0
C)1.73
D)3.0

Question 40

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 $\degree$
B)0 $\degree$
C)-90 $\degree$
D)45 $\degree$

Question 41

An AM radio tuning circuit has a coil with an inductance of 6.00 mH and a capacitor set at 7.50 * 10^-6 mF.What frequency will it detect?

A)550 kHz
B)750 kHz
C)1 060 kHz
D)1 520 kHz

Question 42

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

A)zero.
B)equal to its resistance.
C)a maximum.
D)p/2 W.

Question 43

The primary winding of an electric train transformer has 400 turns, and the secondary has 50.If the input voltage is 120 V(rms), what is the output voltage?

A)480 V
B)60 V
C)15 V
D)10 V

Question 44

An AC power generator produces 25 A (rms) at 3 600 V.The energy is transmitted through a long-distance power line, which has a total resistance of 100 W.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)0.09%
B)1.8%
C)32%
D)69%

Question 45

A transformer is to be designed to increase the 30-kV (rms) output of a generator to the transmission line voltage of 345 kV (rms).If the primary winding has 80 turns, how many turns must the secondary have?

A)6
B)70
C)920
D)9 200

Question 46

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 47

A series RLC circuit in a radio is in resonance with AM 600 kHz.If the radio station is changed to AM 1 200 kHz, by what factor must the capacitance be multiplied to again achieve resonance?

A)4
B)2
C)1/2
D)1/4

Question 48

An FM radio tuning circuit has a coil with an inductance of 0.003 0 mH.What is the value of the capacitance if the set is tuned to 98 MHz?

A)1.8 * 10^-6 mF
B)12 * 10^-6 mF
C)0.98 * 10^-6 mF
D)0.88 * 10^-6 mF

Question 49

An AC power generator produces 50 A (rms) at 3 600 V. The voltage is stepped up to 100 000 V by an ideal transformer, and the energy transmitted through a long-distance power line with a total resistance of 100 W.What is the rms current in the long-distance line?

A)1.0 A
B)1.8 A
C)24 A
D)1 000 A

Question 50

A transformer consists of a 500-turn primary coil and a 2 000-turn secondary coil.If the current in the secondary is 3.00 A, what is the primary current?

A)0.750 A
B)1.33 A
C)12.0 A
D)48.0 A

Question 51

Find the resonant frequency for a series RLC circuit where R = 20.0 W, C = 10.0 µF, and L = 4.0 mH.

A)507 Hz
B)796 Hz
C)1.59 kHz
D)5.00 kHz

Question 52

An AC series circuit contains a resistor of 20 W, an inductor of 30 mH and a variable capacitor.If the frequency of the applied voltage is 500 Hz, to what setting should the capacitor be set if resonance is achieved?

A)0.8 µF
B)1.6 µF
C)2.4 µF
D)3.4 µF

Question 53

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 54

What is the average power dissipation in an RLC series circuit in which R = 100 W, L = 0.1 H, and C = 10 µF driven at resonance by a 100-V (rms) source?

A)100 W
B)500 W
C)1 000 W
D)2 W

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 series circuit contains a resistor of 20 W, a capacitor of 0.75 mF and an inductor of 120 mH.What frequency should be used to create a resonance condition in the circuit?

A)160 Hz
B)320 Hz
C)640 Hz
D)530 Hz

Question 57

A series RLC AC circuit is at resonance.It contains a resistor of 30 W, a capacitor of 0.35 mF and an inductor of 90 mH.If an effective (rms) voltage of 150 V is applied, what is the effective (rms) current when the circuit is in resonance?

A)3.3 A
B)5.0 A
C)9.4 A
D)16.1 A

Question 58

A series RLC circuit has a inductive reactance of 4 W and a capacitive reactance of 1/4 W. By what factor should the AC frequency be changed to put this circuit into resonance?

A)4
B)1/4
C)1/2
D)This circuit cannot be made to achieve resonance.

Question 59

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 60

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 61

Determine the amount of energy carried in l.0 m of a 3.5-mW He-Ne laser beam if the cross-sectional area of the beam is 5.0 * 10^-6 m².

A)0.012 J
B)4.1 * 10^-8 J
C)1.2 * 10^-11 J
D)1.0 J

Question 62

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 63

An electromagnetic wave with a peak electric field component of 1.2 * 10² N/C has what associated peak magnetic field value? (e₀ = 8.85 * 10^-12 C²/N*m², m₀ = 4p * 10^-7 T*m/A and c = 3.00 * 10⁸ m/s)

A)4.0 * 10^-7 T
B)3.6 * 10¹⁰ T
C)2.5 * 10⁶ T
D)2.8 * 10^-11 T

Question 64

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

Question 65

An electromagnetic wave with a peak magnetic field component of 1.5 * 10^-7 T carries what average power per unit area? (m₀ = 4p * 10^-7 T*m/A, e₀ = 8.85 * 10^-12 C²/N*m² and c = 3.00 * 10⁸ m/s)

A)12 W/m²
B)2.7 W/m²
C)3.0 W/m²
D)1.3 W/m²

Question 66

A radio wave transmits 1.2 W/m² average power per unit area.What is the peak value of the associated magnetic field? (m₀ = 4p * 10^-7 T*m/A and c = 3.00 * 10⁸ m/s)

A)1.0 * 10^-7 T
B)8.4 * 10^-3 T
C)1.2 T
D)30 T

Question 67

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 68

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 69

An electromagnetic wave with a peak magnetic field component of 1.5 * 10^-7 T has an associated peak electric field component of what value? (m₀ = 4p * 10^-7 T*m/A, e₀ = 8.85 * 10^-12 C²/N*m² and c = 3.00 * 10⁸ m/s)

A)0.50 * 10^-15 N/C
B)2.00 * 10^-5 N/C
C)2.20 * 10⁴ N/C
D)45 N/C

Question 70

A radar pulse sent out to an airplane at a distance of 20.0 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)66.7 * 10^-6 s
C)133 * 10^-6 s
D)0.033 3 * 10^-6 s

Question 71

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

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

Question 72

A solar cell has a light-gathering area of 10 cm² and produces 0.20 A at 0.80 V (dc) when illuminated with sunlight of intensity 1 000 W/m².What is the efficiency of the solar cell?

A)16%
B)7%
C)23%
D)4%

Question 73

How is the direction of propagation of an electromagnetic wave oriented relative to the associated and fields?

A)parallel to both and

B)perpendicular to both and

C)parallel to , perpendicular to

D)parallel to , perpendicular to

Question 74

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 75

Peak values for a neodymium-glass laser are 600 J for 1 nanosecond.If the cross-section of the laser beam is 1 cm², what are the maximum values of E and B? (µ₀ = 4p * 10^-7 TF*m/A, c = 3.00 * 10⁸ m/s)

A)2 * 10⁹ V/m, 2 T
B)4 * 10⁸ V/m, 7 T
C)2 * 10⁹ V/m, 7 T
D)4 * 10⁸ V/m, 2 T

Question 76

What is the maximum value of the electric field E at 1.0 m from a 100-W light bulb radiating in all directions? (µ₀ = 4p * 10^-7 T*m/A, c = 3.00 * 10⁸ m/s)

A)77 V/m
B)2 000 V/m
C)4 000 V/m
D)6 000 V/m

Question 77

The electric field, , in an electromagnetic wave is oriented in what direction with respect to its associated magnetic field, ?

A) parallel to

B) anti-parallel to

C) perpendicular to

D) at a 45 $\degree$ angle to

Question 78

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 79

A radio wave signal, which transmits at a frequency of 7.20 MHz, has what wavelength? (c = 3.00 * 10⁸ m/s)

A)41.7 m
B)4.17 m
C)28.8 m
D)2.4 * 10^-2 m

Question 80

A radar pulse returns 3.0 * 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)9.0 * 10⁴ m
B)4.5 * 10⁴ m
C)6.0 * 10⁴ m
D)1.0 * 10⁴ m