To measure the voltage drop in a circuit, the voltmeter should be connected in the circuit by:

• A. Disconnecting power, removing the wire leading to the device in question, and wiring the meter in its place.
• B. Placing the test leads in parallel with the device in question.
• C. Removing all but the device in question and measuring the voltage through it.
• D. By placing an ammeter in series with the device.

Answer: (B)

Voltage is the potential difference between two points, so to measure the voltage drop across a device you need to expose those two points to the meter. Placing the voltmeter’s test leads across the device—connecting it in parallel—reads the same voltage difference that exists across the device. The voltmeter is designed with very high input resistance, so it draws only a tiny current and doesn’t disturb the circuit. If the meter were placed in series, it would become part of the current path and would alter the circuit, giving an incorrect reading. The other approaches either replace a wire with the meter or measure current with an ammeter, neither of which properly measures the device’s voltage.