How is AC voltage indicated on a voltmeter?

AC voltage is typically indicated as the RMS (Root Mean Square) value on a voltmeter because this measurement provides a value that accurately represents the effective voltage or power of an alternating current (AC) system. The RMS value is significant because it allows for a comparison between AC voltage and DC (direct current) voltage in terms of how much work can be done by the electrical energy.

Unlike various other methods of measuring AC voltage, RMS takes into account the variations in the waveform over time, providing a measurement that corresponds to the amount of heat produced in a resistor by the AC signal, as if it were a direct current. This makes it particularly useful in practical electrical applications where calculations of power and energy consumption are necessary.

The peak value represents the maximum instantaneous voltage, while the average value reflects an average over the cycle and does not accurately convey the effective voltage in terms of work done. Similarly, the max value may indicate an extreme point in the waveform but lacks the context of power comparison needed for effective measurement in most real-world scenarios. Thus, the RMS value is the most informative and practical way to indicate AC voltage on a voltmeter.