Which instrument uses an electromagnet to measure electric current?

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

Answer: (D)

Measuring current with a magnetic deflection method relies on a coil that forms an electromagnet when current flows. In a galvanometer, this coil sits in a steady magnetic field from a permanent magnet. The current through the coil creates torque in the magnetic field, causing a needle to deflect. The amount of deflection is proportional to the current, and with calibration it reads the current directly. That direct, electromagnet-based current sensing is what makes the galvanometer the instrument designed to measure electric current in this way. Voltmeter and multimeter are primarily used for voltage (and other quantities in the case of a multimeter), and an ammeter is typically a galvanometer with a low-resistance shunt to handle larger currents, but the device fundamentally built around the electromagnet deflection to sense current is the galvanometer.