What instrument is used to measure the flow of electrical current in amperes?

The instrument used to measure the flow of electrical current in amperes is an ammeter. Ammeters are specifically designed to be connected in series within an electrical circuit, allowing them to measure the current flowing through the circuit accurately. This device provides a reading in amperes, which is the standard unit for measuring electric current.

In contrast, a voltmeter measures the potential difference (voltage) across two points in a circuit and is connected in parallel, while an ohmmeter measures the resistance of a component and is not applicable for current measurement. A thermometer is used to measure temperature and does not relate to electrical measurements. Therefore, the ammeter is the appropriate instrument for determining the flow of electric current.