The Moving Coil Galvanometer
Galvanometer is an electromechanical instrument which is used for the detection of electric currents through electric circuits. Being a sensitive instrument, Galvanometer cannot be used for the measurement of heavy currents. However we can measure very small currents by using galvanometer but the primary purpose of galvanometer is the detection of electric current not the measurement of current.The galvanometer consists of a coil, with many turns, free to rotate about a fixed axis in a uniform radial magnetic field. There is a cylindrical soft iron core which not only makes the field radial but also increases the strength of the magnetic field. When a current flows through the coil, a torque acts on it.
where the symbols have their usual meaning. Since the field is radial by design, we have taken sin θ = 1 in the above expression for the torque. The magnetic torque NIAB tends to rotate the coil. A spring S provides a counter torque kφ that balances the magnetic torque NIAB; resulting in a steady angular deflection φ . In equilibrium.
Where k is the torsional constant of the spring .
