A galvanometer is an instrument used to detect and measure small electrical currents. It operates based on the principle of electromagnetic induction and the interaction between a current-carrying conductor and a magnetic field. Here's how a galvanometer works to measure small electrical currents:
Basic Structure: A galvanometer typically consists of a coil of wire suspended between the poles of a permanent magnet. The coil is usually wound around a lightweight frame or spindle, allowing it to rotate freely.
Magnetic Field: The permanent magnet provides a steady magnetic field between its poles. This magnetic field is usually uniform and perpendicular to the plane of the coil.
Current Carrying Coil: When a small electrical current passes through the coil, the coil becomes an electromagnet. The direction of the magnetic field produced by the coil is determined by the direction of the current flowing through it, following the right-hand rule for magnetic fields around a current-carrying conductor.
Interaction with Magnetic Field: The interaction between the magnetic field produced by the coil and the permanent magnetic field causes a torque to act on the coil. This torque causes the coil to rotate around its axis. The rotation is proportional to the strength of the current flowing through the coil.
Restoring Mechanism: The coil is attached to a spring or a torsion mechanism that provides a restoring force. This force opposes the rotation caused by the torque. As the coil rotates, the restoring force increases until it reaches an equilibrium point where the torque and the restoring force balance each other.
Calibration: The galvanometer is calibrated to relate the angle of rotation to the current passing through the coil. This involves applying known currents to the galvanometer and measuring the corresponding angles of rotation. A scale or a pointer is used to indicate the angle of rotation, which in turn provides information about the magnitude of the current.
Sensitive Design: Galvanometers are designed to be extremely sensitive to small currents. This sensitivity is achieved by using lightweight coil assemblies and strong permanent magnets. Additionally, the coil may be wound with many turns of fine wire to increase the magnetic field strength produced by the current.
It's important to note that while galvanometers are excellent at detecting small currents, they are not typically used for accurate measurements in modern applications due to their susceptibility to environmental factors and mechanical limitations. However, they serve as the basis for more advanced instruments like ammeters and voltmeters, which are used for accurate current and voltage measurements in various contexts.