Ampermeter

An ampermeter (or ammeter) is an instrument that measures electric current in amperes through a conductor. The ammeter is placed in series with the component through which current is to be measured, and is constructed with a low internal resistance in order to prevent the reduction of that current as it flows through the instrument itself. Ampere is the amount of electric charge per unit time. So, an ampermeter is an instrument for measuring electric current whose unit is the ampere.

An ampermeter uses magnetic deflection, where current passing through a coil causes the coil to move in a magnetic field. The voltage drop across the coil is kept to a minimum to minimize resistance across the ammeter in any circuit into which it is inserted.