Units and Measurement of Potential Difference

Steps:

• Potential difference (pd) is the energy transferred per unit charge between two points in a circuit.
• The SI unit of pd is the volt (V), defined as one joule per coulomb (J/C).
• Pd is measured across a component by connecting the instrument in parallel to avoid altering the circuit.
• The voltmeter, with high resistance, is the instrument used to measure pd without drawing significant current.

Why D is correct:

• The volt is the standard unit for pd, as per the definition V = W/Q (work per charge), and the voltmeter measures it accurately in parallel.

Why the others are wrong:

• A: Ampere is the unit of current, not pd; ammeter measures current in series.
• B: Ampere is incorrect for pd; voltmeter is right but mismatched with unit.
• C: Volt is correct for pd, but ammeter measures current, not pd.

Final answer: D