What is equivalent to the root-mean-square value of an AC voltage?

The root-mean-square (RMS) value of an AC voltage is defined as the effective value of that voltage, which is equivalent to the DC voltage that would deliver the same power to a load (like a resistor) over time. This means that if you have an AC voltage waveform, the RMS value represents that constant DC voltage which, when applied to a resistive load, would result in the same amount of heat being produced as the AC voltage does over one cycle.

In practical terms, using the RMS value allows you to evaluate the power effectively without having to deal with the varying nature of AC voltages, which oscillate between positive and negative peaks. Hence, the RMS calculation smooths the computation to provide a single value that simplifies the analysis of power.

The other options do not correctly relate to the concept of RMS value. The peak value and the maximum voltage refer to the highest point in the waveform, which does not provide an indication of effective power. Similarly, the average value of the AC voltage does not yield the same heating effect in a resistor as the RMS value does, particularly for non-sinusoidal waveforms.