Basic measurement instruments: Which device is most commonly used to measure electrical potential difference (voltage) across two points in a circuit?

Introduction / Context:
Electric circuits are characterized by voltage, current, resistance, and power. Accurate measurement of these quantities is essential for troubleshooting, design validation, and safety. Identifying the right instrument for each quantity is foundational knowledge.

Given Data / Assumptions:

• We want the instrument that measures potential difference (voltage).
• Measurement is across two nodes in a circuit.
• Standard bench instruments are considered.

Concept / Approach:
A voltmeter measures voltage; it is connected in parallel with the component or nodes of interest and should have a high internal resistance to minimize circuit loading. An ammeter measures current (series connection, low internal resistance). An ohmmeter measures resistance (usually with an internal source). A wattmeter measures power (both voltage and current, often with two elements).

Step-by-Step Solution:
Identify the target quantity: voltage.Select instrument designed for parallel measurement with high input impedance.Answer: Voltmeter.

Verification / Alternative check:
Digital multimeters (DMMs) combine these functions; the “V” mode corresponds to voltmeter operation with high input impedance (e.g., 10 MΩ).

Why Other Options Are Wrong:
Ohmmeter: measures resistance, not live circuit voltage.Ammeter: measures current in series.Wattmeter: measures power, a product of voltage and current.

Common Pitfalls:
Connecting a meter in the wrong configuration (e.g., placing an ammeter in parallel can blow a fuse). Always verify meter mode and leads before measuring.

Final Answer:
Voltmeter