The ammeter is an instrument used for measuring electric current. The current is measured in amperes. There are three main kinds of ammeters: (i) moving coil ammeter (ii) moving iron ammeter and (iii) a hot-wire ammeter.
The moving coil ammeter is like a galvanometer. It has a strip of soft iron which causes to move in the magnetic field created by the current flowing coil.
The moving-iron ammeter has two pieces of iron inside a coil. One of the iron pieces can move. The other piece cannot move. The current passing through the coil produces a magnetic field. The force of the field moves one piece of iron away from the other. A needle attached to the moving piece on a scale indicates the current. These ammeters can measure both direct and alternating current.
A hot-wire ammeter measures the heat produced by an electric current passing through it. The electric current heats a wire, causing it to expand. A needle is attached to indicate how much the wire expands.
The ammeters are used where electrical power is in use. They are common in automobiles and appliances as well as in large machines that use electricity.