AC Ciruits and EM Waves
____
1. In an AC series circuit, the current in a pure resistor differs in phase with the applied voltage by what angle?
a. zero
c. 90°
b. 45°
d. 180°
____
2. The rate of heat dissipation in an AC circuit with resistance, R, and effective current, Irms, is given by which of
the following?
a. 0.5  (Irms)2R
c. 2.0  (Irms)2R
b. (Irms)2R
d. 4.0  (Irms)2R
____
3. The rms current is equal to the direct current that:
a. produces the same average voltage across c.
a resistor as in an AC circuit.
b. dissipates an equal amount of energy in a d.
resistor at the same rate as in an AC
circuit.
provides the same average current in a
resistor as in an AC circuit.
results in the same peak power in a
resistor as in an AC circuit.
____
4. The peak voltage of an AC source is 200 V. What is the rms voltage?
a. 282 V
c. 141 V
b. 200 V
d. 100 V
____
5. In the typical household AC voltage of 120 V, what is the peak voltage?
a. 240 V
c. 120 V
b. 170 V
d. 85 V
____
6. The frequency in an AC series circuit is doubled. By what factor does this change the capacitive reactance?
a. 1/2
c. 2
b. 1/4
d. 4
____
7. In a capacitor in an AC circuit, the voltage:
a. leads the current by 90°.
b.
lags the current by 90°.
c.
d.
may lead or lag the current depending on
the frequency.
is in phase with 70.7% of the current.
____
8. In an AC series circuit, the voltage in the inductor differs in phase with the voltage in the capacitor by what
angle?
a. zero
c. 90°
b. 45°
d. 180°
____
9. 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
c. 1.73
b. 1.0
d. 3.0
____ 10. 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
c. 1.73
b. 1.0
d. 3.0
1
____ 11. 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
c. 3.0
b. 1.0
d. Information is insufficient to determine
answer.
____ 12. The power dissipated in an AC series circuit increases as the phase angle approaches what value?
a. zero
c. 90°
b. 45°
d. 180°
____ 13. Resonance occurs in an AC series circuit when which of the following conditions is met?
a. resistance equals capacitive reactance
c. capacitive reactance equals inductive
reactance
b. resistance equals inductive reactance
d. capacitive reactance equals zero
____ 14. 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
c. 15 V
b. 60 V
d. 10 V
____ 15. An ideal transformer is one that:
a. has a turn ratio, N2/N1, equal to 1.
b. works with direct current.
c.
d.
experiences no power loss.
has an output frequency of 60 Hz.
____ 16. An electromagnetic wave is made up of which of the following oscillating quantities?
a. electrons only
c. magnetic fields only
b. electric fields only
d. electric and magnetic fields
____ 17. An electromagnetic wave with a peak electric field component of 1.2  102 N/C has what associated peak
magnetic field value? (0 = 8.85  1012 C2/Nm2, 0 = 4  107 Tm/A and c = 3.00  108 m/s)
a. 4.0  107 T
c. 2.5  106 T
10
b. 3.6  10 T
d. 2.8  1011 T
____ 18. 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? (0 = 4  107 Tm/A, 0 = 8.85  1012 C2/Nm2 and c = 3.00  108
m/s)
a. 0.50  1015 N/C
c. 2.20  104 N/C
5
b. 2.00  10 N/C
d. 45 N/C
____ 19. An electromagnetic wave with a peak magnetic field component of 1.5  107 T carries what average power
per unit area? (0 = 4  107 Tm/A, 0 = 8.85  1012 C2/Nm2 and c = 3.00  108 m/s)
c. 3.0 W/m2
a. 12 W/m2
2
b. 2.7 W/m
d. 1.3 W/m2
____ 20. A radio wave transmits 1.2 W/m2 average power per unit area. What is the peak value of the associated
magnetic field? (0 = 4  107 Tm/A and c = 3.00  108 m/s)
a. 1.0  107 T
c. 1.2 T
3
d. 30 T
b. 8.4  10 T
2
____ 21. 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 = 4  107 Tm/A, c = 3.00  108 m/s)
a. 77 V/m
c. 4 000 V/m
b. 2 000 V/m
d. 6 000 V/m
____ 22. 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
c. 1.2  10–11 J
–8
b. 4.1  10 J
d. 1.0 J
____ 23. 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
c. 6.62  1026 W
b. 2.34  1030 W
d. 3.74  1026 W
____ 24. If the radiant energy from the Sun comes in as a plane EM wave of intensity 1 340 W/m 2, calculate the peak
values of E and B. (µ0 = 4  107 Tm/A)
c. 330 V/m, 3.35  106 T
a. 330 V/m, 3.0  104 T
6
b. 1 010 V/m, 3.35  10 T
d. 1 010 V/m, 3.0  104 T
____ 25. 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 = 4  107 Tm/A, c = 3.00  108 m/s)
a. 2  109 V/m, 2 T
c. 2  109 V/m, 7 T
8
b. 4  10 V/m, 7 T
d. 4  108 V/m, 2 T
____ 26. 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
c. 6.0  104 m
4
b. 4.5  10 m
d. 1.0  104 m
____ 27. 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
c. 28.8 m
b. 4.17 m
d. 2.4  102 m
____ 28. 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
c. 133  106 s
6
b. 66.7  10 s
d. 0.033 3  106 s
____ 29. The human eye is sensitive to light with wavelength down to 390 nm. What is the frequency of radiation at
this wavelength? (1 nm = 109 m and c = 3.00  108 m/s)
a. 1.8  108 Hz
c. 1.1  1011 Hz
b. 8.5  108 Hz
d. 7.7  1014 Hz
____ 30. An ultraviolet light wave has a wavelength of 300 nm and speed of 2.1  108 m/s through a transparent
medium. What is the frequency of this wave in the medium? (1 nm = 10 9 m and c = 3.00  108 m/s)
c. 7.0  1014 Hz
a. 6.3  102 Hz
b. 9.0  102 Hz
d. 10  1014 Hz
3
____ 31. What value of inductance should be used in a series circuit with a capacitor of 1.8  103 F when designed to
radiate a wavelength of 35 m? (c = 3.00  108 m/s)
a. 3.8 mH
c. 3.8  103 mH
d. 1.9  104 mH
b. 2.6  102 mH
____ 32. What is the wavelength of 100-MHz television EM waves? (c = 3  108 m/s)
a. 0.3 cm
c. 9 km
b. 3 m
d. 10 m
____ 33. Find the frequency of x-rays of wavelength 10 10 m. (c = 3  108 m/s)
a. 3  1018 Hz
c. 6  109 Hz
16
b. 3  10 Hz
d. 3  108 Hz
____ 34. In an RLC circuit, the maximum current is 1 amp. What is the average current?
2A
c. (1/2) A
a.
ÊÁ
ˆ˜
b. ÁÁ 1 / 2 ˜˜ A
d. None of the above.
Ë
¯
____ 35. An RLC circuit has resistance R0, inductance L0, and capacitance C0. If the resistance value is now doubled,
which values of inductance and capacitance will result in the same resonant frequency as before.
a. 2L0, 2C0
c. 2L0, C0/2
d. 2L0, C0
b. L0/2, C0/2
____ 36. What is the effective (rms) current value for an AC current with an amplitude of 10 A?
a. 28 A
c. 7.1 A
b. 3.1 A
d. 14 A
____ 37. An AC voltage source, with a peak output of 200 V, is connected to a 50- resistor. What is the effective (or
rms) current in the circuit?
a. 2.8 A
c. 5.6 A
b. 4.0 A
d. 2.0 A
____ 38. An AC voltage source, with a peak output of 200 V, is connected to a 50- resistor. What is the rate of
energy dissipated due to heat in the resistor?
a. 200 W
c. 566 W
b. 400 W
d. 800 W
____ 39. 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 
c. 100 
b. 120 
d. 72 
____ 40. In an AC series circuit the capacitive reactance is 200  and frequency is 100 Hz. What is the capacitance?
a. 3.2 F
c. 8.0 F
b. 6.28 F
d. 50.0 F
____ 41. 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
c. 8.3  103 s
b. 4.2  103 s
d. 1.7  103 s
4
____ 42. In an AC series circuit the inductive reactance is 50  and the frequency is 100 Hz. What is the inductance in
the circuit?
a. 80 mH
c. 500 mH
b. 240 mH
d. 740 mH
____ 43. What is the impedance of an AC series circuit that is constructed of a 10.0- resistor along with 12.0 
inductive reactance and 7.0  capacitive reactance?
a. 37.0 
c. 27.1 
b. 27.7 
d. 11.2 
____ 44. What is the phase angle of an AC series circuit that is constructed of a 10.0- resistor along with 12.00 
inductive reactance and 7.00  capacitive reactance?
a. 26.6°
c. 87.0°
b. 18.4°
d. 63.4°
____ 45. An AC series circuit has 12.0  resistance, 15.00  inductive reactance and 10.00  capacitive reactance. If
an effective (rms) emf of 120 V is applied, what is the effective (rms) current value?
a. 5.31 A
c. 10.8 A
b. 9.23 A
d. 26.0 A
____ 46. 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
c. 90 V
b. 63 V
d. 125 V
____ 47. 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
c. 95 V
b. 88 V
d. 285 V
____ 48. In an AC circuit, the ratio of average current to maximum current is:
a. zero.
c. 0.707.
b. 0.5.
d. 1.0.
____ 49. A series circuit has equal values for resistance, capacitive reactance, and inductive reactance. The phase angle
for this circuit is:
a. 60°.
c. 180°.
b. –60°.
d. not given.
____ 50. In an RLC series circuit the capacitive reactance is 24 . If the AC frequency doubles, what will be the
resulting capacitive reactance?
a. 24 
c. 48 
b. 12 
d. Additional information is need to find the
value.
____ 51. An AC series circuit has 12.0  resistance, 15.00  inductive reactance and 10.00  capacitive reactance. If
an effective (rms) emf of 120 V is applied, what is the power output?
a. 1 540 W
c. 1 160 W
b. 1 300 W
d. 1 020 W
5
____ 52. The power factor in an AC series circuit is equal to which of the following ratios?
a. resistance to inductive reactance
c. inductive reactance to capacitive
reactance
b. capacitive reactance to inductive
d. resistance to impedance
reactance
____ 53. 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 , what is the average power dissipated in the circuit?
a. 88 W
c. 238 W
b. 176 W
d. 323 W
____ 54. An AC series circuit contains a resistor of 20 , a capacitor of 0.75 F and an inductor of 120 mH. What
frequency should be used to create a resonance condition in the circuit?
a. 160 Hz
c. 640 Hz
b. 320 Hz
d. 530 Hz
____ 55. A series RLC AC circuit is at resonance. It contains a resistor of 30 , a capacitor of 0.35 F 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
c. 9.4 A
b. 5.0 A
d. 16.1 A
____ 56. An AC series circuit contains a resistor of 20 , 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
c. 2.4 µF
b. 1.6 µF
d. 3.4 µF
____ 57. 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
c. 1/2
b. 2
d. 1/4
____ 58. Find the resonant frequency for a series RLC circuit where R = 20.0 , C = 10.0 µF, and L = 4.0 mH.
a. 507 Hz
c. 1.59 kHz
b. 796 Hz
d. 5.00 kHz
____ 59. What is the average power dissipation in an RLC series circuit in which R = 100 , L = 0.1 H, and C = 10 µF
driven at resonance by a 100-V (rms) source?
a. 100 W
c. 1 000 W
b. 500 W
d. 2 W
____ 60. An AM radio tuning circuit has a coil with an inductance of 6.00 mH and a capacitor set at 7.50  106 F.
What frequency will it detect?
a. 550 kHz
c. 1 060 kHz
b. 750 kHz
d. 1 520 kHz
____ 61. 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?
c. 0.98  106 F
a. 1.8  106 F
b. 12  106 F
d. 0.88  106 F
6
____ 62. When an RLC series circuit is in resonance, its impedance is:
a. zero.
c. a maximum.
b. equal to its resistance.
d. /2 .
____ 63. A series RLC circuit has a inductive reactance of 4  and a capacitive reactance of 1/4 . By what factor
should the AC frequency be changed to put this circuit into resonance?
a. 4
c. 1/2
b. 1/4
d. This circuit cannot be made to achieve
resonance.
____ 64. 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
c. 12.0 A
b. 1.33 A
d. 48.0 A
____ 65. 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 .
What is the rms current in the long-distance line?
a. 1.0 A
c. 24 A
b. 1.8 A
d. 1 000 A
____ 66. 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 . 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%
c. 32%
b. 1.8%
d. 69%
____ 67. 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
c. 920
b. 70
d. 9 200
7
ID: A
AC Ciruits and EM Waves
Answer Section
MULTIPLE CHOICE
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A
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B
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ID: A
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