What is the correct way to connect a test voltmeter in a circuit for measuring the voltage across a component?

• A. In series with a unit.
• B. Between source voltage and the load.
• C. Across the supply rails.
• D. In parallel with a unit.

Answer: (D)

To measure the voltage across a component, connect the voltmeter across the two terminals of that component. A voltmeter is designed to measure potential difference, so it must form a parallel path with the component it’s measuring, not a series path.

Why parallel? The voltmeter has a very high internal resistance, so when placed in parallel, only a tiny (negligible) current flows through it. This means it draws almost no current from the circuit and does not disturb the circuit’s operation or the voltage across the component. The reading you see then truly reflects the potential difference between the component’s two points.

If you connect the voltmeter in series, it would become part of the current path, introduce a large resistance, and change how current flows. The voltmeter would not be measuring a voltage drop anymore in the sense of across the component; instead, it would skew the circuit and give an inaccurate reading.

So, place the meter’s leads across the component’s two terminals (positive to the higher-potential terminal, negative to the lower one for DC). This is the correct approach to measure the voltage across a component.