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  • Question
  • A 120 Ω resistor is in parallel with a capacitor with a capacitive reactance of 40 Ω. Both components are across a 12 V ac source. What is the magnitude of the total impedance?


  • Options
  • A. 37.9 Ω
  • B. 3.7 Ω
  • C. 14,400 Ω
  • D. 4,800 Ω

  • Correct Answer
  • 37.9 Ω 


  • RC Circuits problems


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    • 1. When the frequency of the voltage applied to a series RC circuit is increased, the phase angle

    • Options
    • A. increases
    • B. decreases
    • C. remains the same
    • D. becomes erratic
    • Discuss
    • 2. In a series RC circuit, when the frequency and the resistance are halved, the impedance

    • Options
    • A. doubles
    • B. is halved
    • C. is reduced to one-fourth
    • D. cannot be determined without values
    • Discuss
    • 3. A 2 kΩ resistor is in series with a 0.015 µF capacitor across a 15 kHz ac source. What is the magnitude of the total impedance and the phase angle?

    • Options
    • A. 73.4 Ω and ? = ?19.5°
    • B. 707 Ω and ? = ?19.5°
    • C. 2121 Ω and ? = ?19.5°
    • D. 734 Ω and ? = ?38.9°
    • Discuss
    • 4. A capacitor with 150 Ω of capacitive reactance is across an ac source. The impedance, expressed in polar form, is

    • Options
    • A. Z = 150
    • B. Z = 150∠90°Ω
    • C. Z = 150 ∠?90°Ω
    • D. Z = 150∠180°Ω
    • Discuss
    • 5. What is the value of the hypotenuse of a right triangle whose sides are 12 and 18?

    • Options
    • A. 4.24
    • B. 3.46
    • C. 2.16
    • D. 21.63
    • Discuss
    • 6. The voltages in Problem 4 are measured at a certain frequency. To make the capacitor voltage greater than the resistor voltage, the frequency

    • Options
    • A. must be increased
    • B. must be decreased
    • C. is held constant
    • D. has no effect
    • Discuss
    • 7. A certain series resonant circuit has a bandwidth of 2 kHz. If the existing coil is replaced with one having a higher value of Q, the bandwidth will

    • Options
    • A. increase
    • B. remain the same
    • C. decrease
    • D. be less selective
    • Discuss
    • 8. A 200 Ω resistor, a coil with 30 Ω of reactance, and a capacitor of unknown reactance are in series across an ac source. The circuit is at resonance. Circuit impedance

    • Options
    • A. is 230 Ω
    • B. is 170 Ω
    • C. is 200 Ω
    • D. cannot be determined
    • Discuss
    • 9. Referring to Problem 20, what is the total parallel resistance (Rp(tot))?

    • Options
    • A. 4.99 Ω
    • B. 499 Ω
    • C. 4,992 Ω
    • D. 6,800 Ω
    • Discuss
    • 10. A resonant circuit has a lower critical frequency of 7 kHz and an upper critical frequency of 13 kHz. The bandwidth of the circuit is

    • Options
    • A. 7 kHz
    • B. 13 kHz
    • C. 20 kHz
    • D. 6 kHz
    • Discuss


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