Electrical measurements – Core instrument function: An ammeter is designed and connected in a circuit to measure which electrical quantity?

Introduction / Context:
In basic electrical engineering, each instrument has a specific purpose. Understanding what an ammeter measures is fundamental to safe and correct circuit testing and troubleshooting.

Given Data / Assumptions:

• Standard passive or digital ammeter is considered.
• Conventional connection method: series insertion in the circuit branch.
• Ideal ammeter has negligible internal resistance.

Concept / Approach:
Current is the rate of flow of electric charge through a conductor. An ammeter must be placed in series so that the branch current passes through the meter. Its internal resistance must be very low to minimize voltage drop and avoid altering the circuit behavior.

Step-by-Step Solution:
Identify the electrical quantity associated with series measurement and low internal resistance: current.Select the option that states current.

Verification / Alternative check:
Contrast with a voltmeter that is connected in parallel across elements and has high internal resistance to measure voltage without drawing significant current. An ohmmeter measures resistance and must not be connected to a live circuit.

Why Other Options Are Wrong:

• Voltage: measured by a voltmeter in parallel, not by an ammeter.
• Resistance: measured by an ohmmeter or multimeter in resistance mode.
• All of the above: a single-purpose ammeter does not measure multiple quantities simultaneously.
• Power: requires voltage and current; not a direct ammeter reading alone.

Common Pitfalls:
Connecting an ammeter across a source directly, which can cause a short circuit due to very low meter resistance.

Final Answer:
Current