What is a Galvanometer
A Galvanometer is an instrument that is used for the detection of electric currents and voltages. Its working is based on the electromagnetic principle which states that a coil suspended in a magnetic field experiences a torque when an electric current passes through it. This is due to the interaction of the magnetic field in which the coil is suspended with the magnetic field generated around the coil because of the current passing through it. The direction of this torque can easily be found by using Fleming’s right hand rule.
A simple Galvanometer consists of a pair of permanent magnets providing a magnetic field in the horizontal plane. In this magnetic field, a coil wounded over an iron core is suspended on the vertical axis. The two ends of the coil are connected to the outer contacts of the Galvanometer. The Galvanometer is then connected in series in the circuit branch in which the current is to be detected. If an electric current is present, then it will flow through the electric coil of the galvanometer. This coil will then experience a torque and rotate around its vertical axis. This rotation will cause the pointer to deflect from its original position as it is connected to the coil system. An opposing torque, known as the damping torque will also be generated in the coil system by the spring and due to the generation of the eddy currents in the iron core. The pointer will reach a steady state when the two opposing torques reach an equilibrium.
One of the important parameters of a galvanometer is its sensitivity which should be high in order to detect small currents. This is why an iron core is used in a galvanometer as it provides a path of low reluctance to the magnetic field thereby increasing the amount of torque that the coil experiences for the same amount of current than in case of an air core. Another alternative arrangement that can be used to increase this sensitivity is to use an air core but decrease the radius of the coil, thereby decreasing its moment of inertia.
The practical application of Galvanometer is in potentiometer bridges that are used for the measurement of resistance values. Here the galvanometer is used for the detection of the null current condition. A Galvanometer can also be used for the measurement of the amount of current passing through it by calibrating the deflection of the pointer.