08-12-2017, 10:39 AM
The tangent galvanometer was first described in an 1837 article by Claude-Servais-Mathias Pouillet (1790-1868), who later used this sensitive form of galvanometer to verify Ohm's law. To use the galvanometer, it is first configured on a level surface and the coil is aligned with the north-south magnetic direction. This means that the needle of the compass in the middle of the coil is parallel to the plane of the coil when it is not carrying current. The current to be measured is now sent through the coil, and produces a magnetic field, perpendicular to the plane of the coil, and directly proportional to the current. The magnitude of the magnetic field produced by the coil is B; the magnitude of the horizontal component of the earth's magnetic field is B '. The compass needle is aligned along the vector sum of B and B 'after rotating through an angle Ø from its original orientation. The vector diagram shows that tan Ø = B / B '. Since the magnetic field of the earth is constant, and B depends directly on the current, the current is therefore proportional to the tangent of the angle through which the needle has rotated.
A galvanometer is an electromechanical instrument to detect and indicate electrical current. A galvanometer works like an actuator, producing a rotating deflection (of a "pointer"), in response to electrical current flowing through a coil in a constant magnetic field. Early galvanometers were not calibrated, but their later developments were used as measuring instruments, called ammeters, to measure the current flowing through an electrical circuit.
The galvanometers were developed from the observation that the needle of a magnetic compass is deflected near a cable that has an electric current flowing through it, first described by Hans Oersted in 1820. They were the first instruments used to detect and measure small amounts of electric currents. André-Marie Ampère, who gave mathematical expression to the discovery of Ørsted and appointed him by the Italian electricity researcher Luigi Galvani, who in 1791 discovered the principle of the frogs galvanoscope, that electric current would cause the legs of a dead frog to shake.
