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

Explanation

Poles of field magnet of moving coil galvanometer are made concave due to the fact that radial field between the two circular [or concave] poles, the field is always normal to the surface of the coil. Hence, magnatic field is always normal , whatever be the position of coil i.e.,` theta = 0^(@).`
Deflectiong torque, `tau = IBn A cos 0^(@)`
`tau = IBn A =` maximum
for all positions of the coil within magnetic field.