Alternating Current and Voltage — Engineering Board Exam Practice Questions

25 free engineering board exam reviewer questions on Alternating Current and Voltage (AC Circuits), each with the correct answer and a worked solution.

  1. Two currents i1=10 t A and i2=10 ( t+120°) A flow into a junction and add. What is the peak value of the total current?
  2. How long does it take a 400 Hz sine voltage, starting at zero, to reach 70.7% of its peak value for the first time?
  3. A sinusoidal voltage has an rms value of 120 V. At what angle in the first quadrant of the cycle does its instantaneous value equal 100 V?
  4. The rectangular pulse train shown has a period of 10 ms and is at 20 V for the first 4 ms of each period and zero for the rest. Find its…
  5. The voltage shown is a sine wave riding on a dc level (it swings between -10 V and +30 V). Find its rms value.
  6. Two series-connected sources produce v1=30 t V and v2=40 ( t+90°) V. What is the peak value of the total voltage?
  7. A sinusoidal voltage with a peak value of 100 V is applied across a 50, resistor. What average power does the resistor dissipate?
  8. How long does a 60 Hz sine wave take to go from zero to 45° of its cycle?
  9. Given v=100 ( t+20°) V and i=8 ( t-40°) A, which statement is correct?
  10. A voltage is given by v=311 (377t) V. What is its frequency?
  11. The waveform shown is a full-wave rectified sine voltage. Find its average (dc) value.
  12. The waveform shown is a half-wave rectified sine voltage. Find its average (dc) value over a complete cycle.
  13. Find the rms value of the triangle wave shown.
  14. What is the rms value of the symmetrical square wave shown?
  15. Two sinusoids of the same frequency are plotted below: a voltage v (solid) and a current i (dashed). Use the time axis (milliseconds, one…
  16. The voltage v (solid) and the current i (dashed) plotted below have the same frequency. What is their phase relationship? (The time axis…
  17. The sinusoidal voltage shown has a period of 12 ms and a peak value of 50 V. What is its instantaneous value at t=1.5 ms?
  18. Which expression describes the voltage waveform shown?
  19. What is the average value of a sine wave over one complete cycle?
  20. A sinusoidal voltage has a peak value of 311 V. What is its rms value?
  21. A voltmeter reads 120 V on an ac line. What is the peak value of the voltage?
  22. Find the angular frequency of a 50 Hz source.
  23. What is the period of a 60 Hz ac voltage?
  24. What is the rms value of the sinusoidal voltage shown in the plot?
  25. The sinusoidal voltage shown is plotted against time in milliseconds. Find its frequency.