galvanometer

A galvanometer is an instrument for detecting and measuring small electric currents by the deflection of a pointer. It operates on the principle that a current-carrying coil placed in a magnetic field experiences a torque that tends to rotate the coil; the resulting angular deflection is proportional to the current, within a usable range.

Most common form is the moving-coil galvanometer, also known as the d'Arsonval movement. A coil of fine wire is suspended in a strong, uniform magnetic field produced by permanent magnets. The coil rotation is resisted by a restoring torque from springs, yielding a nearly linear response and high sensitivity.

Other forms include moving-iron galvanometers, in which a soft-iron vane deflects within the field of a coil, allowing larger currents at the expense of linearity and speed. These were more common in earlier instruments.

Applications include detecting and measuring small currents in laboratories, and serving as the sensitive element in voltmeters and ammeters when used with shunts or multipliers. Modern practice often uses digital meters, but galvanometer movement remains in teaching labs and certain sensor applications.

History: the galvanometer arose in the 19th century for current measurement. The moving-coil variant was refined in the late 19th century by Jacques-Arsène d'Arsonval, giving a highly sensitive and linear instrument that later formed the basis of many traditional meters.