Why are pole pieces of galvanometer made concave?

Why are pole pices of galvanometer made concave?

Why is the pole pieces of a magnet are concave shaped in a moving coil galvanometer ? What is the role of soft iorn cylinder kept within the coil of the moving coil of the galvanometer ?

Why are pole pieces of.a moving coil galvanometer made concave ?

Why are poles of field magnet of moving coil galvanometer made concave inshape?

Why are the pole pieces of a horseshoe magnet in a moving coil galvanometer made cylinddrical in shape?