Which instrument measures electrical current?

• A. Voltmeter
• B. Ammeter
• C. Ohmmeter
• D. Wattmeter

Answer: (B)

To measure electrical current, you need an instrument that the current can flow through, because current is the rate of charge flow in a conductor. An ammeter is designed for this job; it’s placed in series with the circuit so all the current goes through it. It has very low internal resistance, which minimizes the voltage drop and makes the circuit behave as if the meter weren’t there, so the reading reflects the true current. In contrast, a voltmeter is connected in parallel across a component to measure voltage and is designed with high internal resistance to avoid drawing current. An ohmmeter measures resistance by applying a small current when the circuit is de-energized, and a wattmeter measures power by combining measurements of voltage and current. So, for measuring how much current is flowing, the instrument used is the ammeter.