Ammeter
An ammeter is an instrument that is used to measure the current.
It is usually in the form of a small box with two sockets to connect wires to an electric circuit. There would either be a pointer and scale, or a digital screen, to show the reading.
In order to use it, it must be connected in series in a circuit. This means that we must first cut a wire in the circuit, or replace that wire by two separate wires. Then we connect the open end of each wire to the leads (wires) from the ammeter.
Depending on the type of circuit, the current can be quite big, or quite small. So it is convenient to have the option to select different ranges for the reading.
On a digital ammeter, there is usually a knob to turn, so you can select a certain range. For example, if you turn the knob to point at label 'A', it could only be able to show readings from 0.01 to 10 A.
To measure currents smaller than 0.01 A, you have to turn the knob to point to 'mA'. 1 mA = 0.001 A. Then it could read from 0.1 to 10 mA.
To make it easy to draw a circuit, we usually use a symbol with the letter 'A' in circle to represent an ammeter.
