What is the importance of radial magnetic field in a moving coil galvanometer?

To produce a constant torque on the coil because if we dont apply a radial magnetic field the relation between current and the angle is non linear thus current cant be measured easily and conveniently in terms of deflection in coil because we will get the observation in terms of deflection! 

max torque will be experienced such that it is uniform in all orienttions of the coil which facilitates an increase in the sensitivty of the mcg

it keeps angle zero so the value of sin of angle is zero wich is helfull in determining the value of torque torque is given by NIAB

CBSE BOARD ANSWER: The radial magnetic field is always parallel to the plane of the coil of the galvanometer, and provides constant torque irrespective of the rotation of the coil. This makes the deflection directly proportional to the current, and facilitates easy calibration of the galvanometer scale. [Taken from offician marking scheme.]

As field is radial to the coil means it is parallel to field and we know that area vector of coil is perpendicular to it`s plane and hence the magnetic moment is also perpendicular. Since field and plane of coil are parallel then the field and magnetic moment will also perpendicular giving max torque.....

It is parallel to the magnetic field and it is necessary to produce constant torque and to increase the sensitivity of the galvanometer

Dear student,

 

The radial magnetic field is applied to produce a constant torque on the coil. It gives the relation between the current and the angle which is non-linear such that the current cannot be measured easily. This makes the deflection directly proportional to the current, and facilitates easy calibration of the galvanometer scale.

 

Hope it helps

Thanks and regards,

Kushagra