M3 Cat A M3.13 AC Theory

What is the main characteristic that distinguishes AC from DC?

• In AC the amount (size) of voltage remains constant.

• In AC the direction (polarity) of current remains constant.

• In AC the amount (size) of both voltage and current changes with time.

• In AC the direction (polarity) of both voltage and current changes with time.

Which statement accurately describes common AC?

• The changes in voltage and current never repeat.

• The average voltage and current are always positive.

• The voltage and current vary sinusoidally with time.

• The current remains constant over time.

What does the term "phase difference" refer to?

• The difference in size between voltage and current.

• The time it takes for a wave to complete one cycle.

• The relative displacement between two points in a cycle of two waveforms.

• The amount of current flowing through a circuit.

What is the unit of frequency?

• Hertz (Hz)
• Volt (V)

• Watt (W)

• Seconds (s)

What is the amplitude of an AC waveform?

• The average value of voltage or current over a full cycle.

• The peak value of voltage or current.

• The instantaneous value of voltage or current.

• The root mean square value of voltage or current.

What is the instantaneous value of an alternating voltage or current?

• The peak value of the voltage or current
• The average value of the voltage or current
• The root mean square value of the voltage or current
• The value at a particular instant, which may vary between zero and the peak value.

How is the average voltage over one half cycle of an AC waveform calculated?

• By dividing the peak voltage by π.

• By summing equally spaced instantaneous values of the half cycle and dividing by the number of mid-ordinates.

• By taking the square root of the peak voltage.

• By finding the difference between peak and peak-to-peak voltage

What does RMS value represent in AC voltage or current?

• The maximum value of voltage or current.

• The average value of voltage or current over a full cycle.

• The difference between peak and peak-to-peak voltage.

• The value which, when applied to a resistance, will produce the same power output as an equivalent DC current or DC voltage.

What defines a square waveform?

• It rises quickly to a particular amplitude, remains constant for a time period, and drops fast at the end.

• It is a waveform with a symmetrical shape and equal rise and fall times.

• It oscillates between positive and negative peak values.

• It has a steady rate of change of voltage over each half cycle.

What is the characteristic duty cycle of a square waveform?

• 50%
• 10%

• 75%
• 25%