Explain construction and principle of moving coil galvanometer.

Explanation

1. Moving coil galvanometer is as shown in diagram.

2. The galvanometer consists of a coil with many turns, free to rotate about a fixed axis in a uniform radial magnetic field.
3. There is a cylindrical soft iron core which not only makes the field radial but also increases the strength of the magnetic field.
4. Magnetic field is uniform between space of two pole so it always be `90^(@)` between area of the coil and `vecB` (magnetic field)
`therefore(theta=90)`
So, torque on loop is,
`tau=NBIAsintheta` which is maximum. So coil rotate.
5. A spring `S_(p)` provides a counter torque `K_(phi)` that balances the magnetic torque, NIAB resulting in a steady angular deflection.
6. The deflection is indicated on the scale by a pointer attached to the spring which measure the value of electric current.
7. Principle : A current carrying coil placed in a magnetic field experience a current dependent torque which tends to rotate the coil and produces angular deflection.