A voltmeter is connected to measure voltage in a circuit. In which configuration should it be connected?

• A. In series
• B. In parallel
• C. Across the conductor
• D. Across the source

Answer: (B)

To measure voltage, place the voltmeter across the two points where the voltage is defined so it can read the potential difference between them. A voltmeter has a very high resistance, so when connected in parallel with the component or across the points of interest, it draws only a tiny current and samples the voltage without significantly disturbing the circuit. If you put the voltmeter in series, it becomes part of the current path and its high resistance would alter the circuit’s operation, leading to an inaccurate reading. While you could measure the source voltage by placing the meter across the source, the general practice for measuring a component’s voltage is to connect the voltmeter in parallel with that component or across the two points where the voltage is defined.