Which device is used to measure electrical current?

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

Answer: (A)

Measuring electrical current requires an instrument that sits in the path of the current so every amp flows through it. The ammeter is designed for this purpose; it’s connected in series with the circuit and has very low internal resistance so it doesn’t appreciably change the current or voltage in the circuit. It directly reads amperes, the unit of current.

Voltmeter, by contrast, is used to measure voltage and is connected in parallel with a component because it needs to measure the potential difference without drawing significant current. An ohmmeter measures resistance by applying a small current and observing the resulting voltage, typically when circuits are de-energized. A wattmeter measures power by combining voltage and current (and sometimes power factor).

So, for measuring current specifically, the ammeter is the correct instrument.