what is the function of the soft iron core in a moving coil galvanometer
Your friend has answered this question very well. Keep it up Asmita!
The soft iron core is spherical if the coil is circular and cylindrical if the coil is rectangular. It makes the magnetic field linked with the coil to be a radial field ie the plane of the coil in all positions remains parallel to the direction of magnetic field.
see the diagram of the moving coil galvanometer below:
. Therefore torque produced = NIBAcos Ө,
where Ө =00.
ie maximum torque is produced.
Also the retentivity of soft iron core is low, which increases the sensitivity of the galvanometer ie the moment current becomes 0 , the galvanometer will show 0 deflection.
By increasing the permeability of the core the mageic dipole moment of the core can be increased when the current flows through the galvanometer. This increases the sensitivity of the galvanometer, Since the soft iron has low retentivity as soon as the current stops the magnetic power of the core is lost.
(i) The uniform radial magnetic field keeps the plane of the coil always parallel to the direction of the magnetic field. That is, the angle between the plane of the coil and the magnetic field is zero in all the orientations of the coil.
(ii) The soft iron core increases the strength of the magnetic field.