Instrument function: An ammeter is used in electrical measurements to determine which quantity in a circuit?

Introduction / Context:
Accurate measurement is central to electrical diagnostics. Instruments are designed for specific quantities: voltmeters for voltage, ammeters for current, and ohmmeters for resistance. Misusing instruments can lead to incorrect readings or equipment damage. This question checks the basic purpose of an ammeter.

Given Data / Assumptions:

• The ammeter is a standard series-connected instrument with low internal resistance.
• We are considering conventional bench or handheld meters (digital or analog).
• Measurement is in DC or AC as supported by the meter.

Concept / Approach:

An ammeter measures current and must be placed in series with the circuit branch so that all the branch current flows through it. Its internal shunt design minimizes voltage drop. By contrast, a voltmeter has high internal resistance and is placed in parallel across components. Ohmmeters inject a small test current to infer resistance with the circuit de-energized.

Step-by-Step Solution:

Verification / Alternative check:

Use Ohm’s law cross-check: if you also know the voltage across a known resistor, I = V / R should match the ammeter reading (within meter tolerances).

Why Other Options Are Wrong:

Voltage is measured by a voltmeter, resistance by an ohmmeter or DMM resistance mode. 'None of the above' is incorrect because the ammeter’s role is well-defined.

Common Pitfalls:

Connecting an ammeter across a voltage source (parallel) can cause a short circuit; always insert in series. Selecting the wrong range can overload the meter.

Final Answer:

current