Question 3-74L3

A voltmeter measures voltage by passing a small current through a sensitive meter movement. Each meter movement has a specific full-scale deflection (FSD) current and a corresponding internal resistance, which means it can only directly measure a very limited voltage range. To measure higher voltages, a resistor, known as a series multiplier, is placed in series with the meter movement. According to Ohm's Law ($V = I \times R$), adding this series resistance increases the total resistance of the voltmeter circuit. For the same FSD current to flow, a proportionally higher total voltage must be applied across the entire series combination (multiplier + meter movement). The multiplier resistor "drops" the majority of this higher voltage, leaving only the safe FSD voltage across the meter movement itself. Thus, the meter can indicate a much higher total voltage, effectively *increasing* its voltage-indicating range. Option B is incorrect because series multipliers are essential components in multi-range voltmeters. Option C is incorrect; adding series resistance increases, rather than decreases, the voltage range. Option D describes a "shunt" resistor, which is placed in *parallel* with an ammeter movement to increase its current-indicating range, a different application.