Gibilisco - Power And Resonance In Alternating-current Circuits

20 Questions | Total Attempts: 400

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Gibilisco - Power And Resonance In Alternating-current Circuits

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Questions and Answers
  • 1. 
    The power in a pure reactance is
    • A. 

      Radiated.

    • 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. 

      The load impedance

    • B. 

      The load resistance

    • 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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