A DC voltmeter is capable of measuring a maximum of300 volts. If it is used to measure the voltage across a device operating at 220-volt AC supply, the reading of the voltmeter will be

A DC voltmeter, typically a moving-coil instrument, is designed to measure the average value of the voltage applied across its terminals [t4]. In a standard 220-volt AC supply, the voltage is sinusoidal, meaning it alternates symmetrically between positive and negative peaks [t4][t5]. The average value of a sinusoidal waveform over a complete cycle is exactly zero because the positive half-cycle cancels out the negative half-cycle [t1][t4][t8]. Since the frequency of a standard AC supply (typically 50Hz) is much higher than the mechanical response time of a DC voltmeter's needle, the instrument cannot track the instantaneous changes and instead settles at the mean value [t3]. Consequently, despite the 220V RMS value and the 311V peak value of the AC supply [t4][t7], the DC voltmeter will show a reading of 0 volts [t1][t3].