Which instrument measures current in amperes when placed in series with a circuit?

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

Answer: (A)

Measuring current requires inserting the instrument directly in the path of the circuit so the same current flows through it as through every component in that path. An ammeter is built for this purpose and is connected in series; it has very low internal resistance so it doesn’t significantly alter the circuit current.

Other meters are designed for different quantities. An ohmmeter measures resistance and is used across a component (often with the circuit de-energized), not in series with a live circuit. A voltmeter measures potential difference and is wired in parallel with the component, and it has high resistance to avoid drawing current. A multimeter can measure multiple quantities, including current, but when measuring current it must be placed in series and configured to current mode.

So, the instrument that measures current in amperes when placed in series with a circuit is the ammeter.