Which quantity represents the peak voltage of an AC waveform?

• A. E(rms)
• B. E(average)
• C. E(max)
• D. E(inst)

Answer: (C)

Peak voltage is the amplitude—the maximum value the waveform reaches during a cycle. For a sinusoidal voltage, v(t) = Vp sin(ωt), the largest magnitude is Vp, which is the peak voltage.

RMS, or E(rms), is the effective value that gives the same heating effect in a resistor and for a sine wave equals Vp/√2, not the peak. The average value over a full cycle, E(average), is zero for a symmetric AC signal because positive and negative halves cancel out; it doesn’t represent the waveform’s maximum. The instantaneous value, E(inst), is the voltage at a specific moment in time and varies from moment to moment—only at the moment when sin(ωt) is ±1 do you hit the peak.

So the quantity that represents the peak voltage is the maximum value, E(max).