An ammeter is an instrument used to measure electric current, which is the flow of electric charge. While an ammeter measures the current, it does not directly measure the flow of individual electrons. Instead, it measures the overall rate of charge flow through a conductor.
The working principle of an ammeter is based on the fact that an electric current passing through a conductor creates a magnetic field around it. The ammeter utilizes this principle to measure the strength of the magnetic field, which is directly proportional to the current flowing through the conductor.
Typically, an ammeter is connected in series within a circuit, meaning the current being measured passes through the ammeter itself. Inside the ammeter, there is a coil of wire, known as a current sensing coil or shunt, which is made of a material with low resistance. When current flows through the circuit, it also flows through this coil.
The current passing through the coil creates a magnetic field around it. The strength of this magnetic field is directly proportional to the current flowing through the circuit, as described by Ampere's law. The ammeter is designed such that the magnetic field produced by the current in the coil interacts with a permanent magnet or a set of fixed coils, generating a torque or force.
The torque or force deflects a needle or a pointer on a scale, indicating the value of the current being measured. In digital ammeters, the torque or force is converted into an electrical signal and displayed numerically on a digital screen.
So, while an ammeter does not directly measure the flow of individual electrons, it measures the overall current by detecting the magnetic field generated by the flow of electric charge through a conductor.