A voltmeter having a range of 150 volts and an internal resistance of 150 000 ohms is to be extended to read 750 volts. The required multiplier resistor would have a value of:

First, determine the full-scale current of the original voltmeter using Ohm's Law (I = E / R). Dividing 150 volts by 150,000 ohms gives a full-scale current of 1 mA (0.001 amps). To measure a new full-scale voltage of 750 volts, the total resistance of the circuit must be calculated using the same current: R = 750 V / 0.001 A = 750,000 ohms. Because the meter already provides 150,000 ohms of resistance internally, the new series multiplier resistor needed is the difference between the total needed resistance and the existing resistance. Subtracting 150,000 from 750,000 yields the required multiplier of 600,000 ohms.