Where would the voltmeter read full source voltage in a single-load circuit?

Where would the voltmeter read full source voltage in a single-load circuit?

• A. After the load
• B. Across the load
• C. Across the source
• D. Before the load

Answer: (D)

The voltmeter reads the potential difference between its two leads, and you want to see the entire source emf. To do that, connect the voltmeter across the source’s terminals, i.e., at the point before the current enters the load. In a single-load circuit, the full voltage the source can supply appears across its terminals, so measuring there gives you the full source voltage. If you measure across the load (or after it), you’re measuring the drop across the load (or what remains after any internal drops), which may not show the full source emf, especially in real sources with internal resistance.

The voltmeter reads the potential difference between its two leads, and you want to see the entire source emf. To do that, connect the voltmeter across the source’s terminals, i.e., at the point before the current enters the load. In a single-load circuit, the full voltage the source can supply appears across its terminals, so measuring there gives you the full source voltage. If you measure across the load (or after it), you’re measuring the drop across the load (or what remains after any internal drops), which may not show the full source emf, especially in real sources with internal resistance.