Instrumentation basics: which instrument is most commonly used to measure the opposition to current flow (i.e., electrical resistance) in a circuit?

Introduction / Context:
Accurate electrical measurements are fundamental to diagnostics and design. Resistance—the opposition to current flow—is one of the three cornerstone quantities alongside voltage and current. This question checks recognition of the proper instrument used to measure resistance in circuits and components.

Given Data / Assumptions:

• The task is to identify the instrument that measures resistance.
• We assume standard bench or handheld meters.
• No unusual measurement setups (e.g., Kelvin connections for very low resistance) are implied.

Concept / Approach:
An ohmmeter measures resistance directly, usually by sourcing a small known current and measuring the resulting voltage drop, then computing R using R = V / I. Modern digital multimeters integrate ohmmeter, ammeter, and voltmeter functions in one device, but the resistance mode is specifically the ohmmeter function.

Step-by-Step Solution:
1) Define the quantity: resistance represents opposition to current, measured in ohms (Ω).2) Recall instrument associations: ammeter → current, voltmeter → voltage, ohmmeter → resistance, wattmeter → power.3) Select the instrument designed to measure resistance directly: the ohmmeter.

Verification / Alternative check:
Inspect a DMM: the “Ω” setting corresponds to the ohmmeter mode. When activated, the meter injects a test signal and displays the calculated resistance value.

Why Other Options Are Wrong:

• Ammeter: Measures current (A), not resistance.
• Voltmeter: Measures potential difference (V), not resistance.
• Wattmeter: Measures power (W), not resistance.
• None of the above: Incorrect because “Ohmmeter” is correct.

Common Pitfalls:
Attempting to infer resistance from separate voltage and current readings is valid (R = V / I) but indirect; an ohmmeter provides a direct and safer measurement for passive components.

Final Answer:
Ohmmeter.