Question

What is special about a radial magnetic field? Why is it useful in a moving coil galvanometer?

Answer 1

A radial magnetic field is one in which the magnetic field lines remain parallel to the plane of the coil for every position of the moving coil.

Therefore, the angle between the magnetic field \[\vec B\] and the normal to the coil is always 90°. Hence,

τ = NIAB sin 90°

So, the deflecting torque is directly proportional to the current II.

This is useful in a moving coil galvanometer because it gives a uniform scale, i.e. equal changes in current produce equal changes in deflection.