Which device is commonly used for measuring electric current?

The device commonly used for measuring electric current is the ammeter. This instrument is specifically designed to measure the flow of electric current in a circuit, which is expressed in amperes (A). It works by being connected in series within the circuit, allowing it to gauge the amount of current flowing through that part of the circuit without significantly affecting the circuit's operation.

In contrast, the voltmeter is used to measure voltage across two points in a circuit, indicating the potential difference rather than the flow of current. The megger is primarily used for insulation resistance testing and is not designed to measure current. The oscilloscope is a tool for visualizing waveforms of electrical signals, providing a graphical representation of varying voltages over time rather than directly measuring current. Hence, the ammeter stands out as the appropriate choice for measuring electric current.