# Gibilisco - Power And Resonance In Alternating-current Circuits

20 Questions | Total Attempts: 400  Settings  .

• 1.
The power in a pure reactance is
• A.

• B.

True.

• C.

Imaginary.

• D.

Apparent.

• 2.
Which of the following is not an example of true power?
• A.

Power in the form of heat, produced by dc flowing through a resistor

• B.

Power in the form of electromagnetic fields, radiated from a radio antenna

• C.

The product of the rms ac through a capacitor and the rms voltage across it

• D.

Power in the form of heat, produced by losses in an RF transmission line

• 3.
Suppose the apparent power in a circuit is 100 W, and the imaginary power is 40 W. What isthe true power?
• A.

92 W

• B.

100 W

• C.

140 W

• D.

It is impossible to determine from this information.

• 4.
Power factor is equal to
• A.

Apparent power divided by true power.

• B.

Imaginary power divided by apparent power.

• C.

Imaginary power divided by true power.

• D.

True power divided by apparent power.

• 5.
Suppose a circuit has a resistance of 300 Ω and an inductance of 13.5 µH in series, and isoperated at 10.0 MHz. What is the power factor?
• A.

0.334

• B.

0.999

• C.

0.595

• D.

It cannot be determined from the information given.

• 6.
Suppose a series circuit has Z = 88.4 Ω, with R = 50.0 Ω. What is the power factor, expressed as a percentage?
• A.

99.9 percent

• B.

56.6 percent

• C.

60.5 percent

• D.

29.5 percent

• 7.
Suppose a series circuit has R = 53.5 Ω, with X = 75.5 Ω. What is the power factor, expressed as a percentage?
• A.

70.9 percent

• B.

81.6 percent

• C.

57.8 percent

• D.

63.2 percent

• 8.
The phase angle in an ac circuit is equal to
• A.

Arctan (Z/R).

• B.

Arctan (R/Z).

• C.

Arctan (R/X).

• D.

Arctan (X/R).

• 9.
Suppose an ac ammeter and an ac voltmeter indicate that there are 220 W of VA power in acircuit that consists of a resistance of 50 Ω in series with a capacitive reactance of −20 Ω. What is the true power?
• A.

237 W

• B.

204 W

• C.

88.0 W

• D.

81.6 W

• 10.
Suppose an ac ammeter and an ac voltmeter indicate that there are 57 W of VA power in acircuit. The resistance is known to be 50 Ω, and the true power is known to be 40 W. What is the absolute-value impedance?
• A.

50 Ω

• B.

57 Ω

• C.

71 Ω

• D.

It is impossible to determine on the basis of this data.

• 11.
Which of the following should be minimized in an RF transmission line?
• A.

• B.

• C.

The line loss

• D.

The transmitter power

• 12.
Which of the following does not increase the loss in a transmission line?
• A.

Reducing the power output of the source

• B.

Increasing the degree of mismatch between the line and the load

• C.

Reducing the diameter of the line conductors

• D.

Raising the frequency

• 13.
Which of the following is a significant problem that standing waves can cause in an RFtransmission line?
• A.

Line overheating

• B.

Excessive power loss

• C.

Inaccuracy in power measurement

• D.

All of the above

• 14.
Suppose a coil and capacitor are in series. The inductance is 88 mH and the capacitance is1000 pF. What is the resonant frequency?
• A.

17 kHz

• B.

540 Hz

• C.

17 MHz

• D.

540 kHz

• 15.
Suppose a coil and capacitor are in parallel, with L = 10.0 µH and C = 10 pF. What is fo?
• A.

15.9 kHz

• B.

5.04 MHz

• C.

15.9 MHz

• D.

50.4 MHz

• 16.
Suppose you want to build a series-resonant circuit with fo = 14.1 MHz. A coil of 13.5 µH isavailable. How much capacitance is needed?
• A.

0.945 µF

• B.

9.45 pF

• C.

94.5 pF

• D.

945 pF

• 17.
Suppose you want to build a parallel-resonant circuit with fo = 21.3 MHz. A capacitor of22.0 pF is available. How much inductance is needed?
• A.

2.54 mH

• B.

254 µH

• C.

25.4 µH

• D.

2.54 µH

• 18.
A 1⁄4-wave section of transmission line is cut for use at 21.1 MHz. The line has a velocityfactor of 0.800. What is its physical length in meters?
• A.

11.1 m

• B.

3.55 m

• C.

8.87 m

• D.

2.84 m

• 19.
What is the fourth harmonic of 800 kHz?
• A.

200 kHz

• B.

400 kHz

• C.

3.20 MHz

• D.

4.00 MHz

• 20.
Suppose you want to build a 1⁄2-wave dipole antenna designed to have a fundamentalresonant frequency of 3.60 MHz. How long should you make it, as measured from end to end in feet?
• A.

130 ft

• B.

1680 ft

• C.

39.7 ft

• D.

515 ft

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