Question

The magnetic field is made radial in a galvanometer
(A) To make field stronger
(B) To make field weaker
(C) To make scale linear
(D) To reduce its resistance

Answer 1

Hint: The magnetic field is made radial in a galvanometer to concentrate the field in a circular region uniformly in all directions and hence, make it linear in angular direction.

Complete step by step solution
Let us briefly recap what the purpose and design goal of a galvanometer is and what is the purpose of the radial magnetic field in it. The moving coil galvanometer consists of a rectangular coil with a huge number of windings of a thin insulated copper wire. This coil is suspended between the poles of a permanent magnet having hemispherical poles (like in a horseshoe magnet). The purpose of making the poles hemispherical is to apply a uniform radial magnetic field over the coil.
Had the magnetic field not been radial, the magnetic field and eventually, the magnetic flux through the coil would vary at different angular positions of the coil. Hence there would be unnecessary spikes and unresponsiveness in the galvanometer. We need the rotation to be smooth i.e. the angle of rotation should increase linearly with increase in the current.

Therefore, option (C) is the correct option.

Note: Here is a diagram of a moving coil galvanometer for better understanding.


As you can see from the diagram, a radial magnetic field will ensure that there is always a component of magnetic field perpendicular to the plane of the coil to ensure maximum magnetic flux/field/torque.