An ammeter is best described as which of the following?

• A. A device that measures voltage across a circuit.
• B. An instrument installed in series with a load to measure current.
• C. A device that measures air density.
• D. A device that calibrates compass heading.

Answer: (B)

An ammeter measures the flow of electric current in a circuit. To do this accurately, it must be installed in series with the load so the same current that powers the load flows through the meter. Its very low internal resistance minimizes any voltage drop and prevents significantly altering the circuit. Placing it in parallel would create a near-short circuit path and distort readings or cause damage.

Other instruments perform different tasks: a device used to measure voltage is connected in parallel across a component; a device that measures air density isn’t electrical instrumentation; a device that calibrates compass heading relates to navigation, not electrical current.