Why should the spring/suspension wire in a moving coil gavanometer have a low torsional constant?

Why should an ammeter have a low resistance?

Why is the core of moving coil galvanometer laminated?

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 can we not use the ordinary moving coil galvanometer for measureing a.c. current and voltage?

A rectangular coil of area 5.0xx10^(-4) m^2 and 60 turns is pivoted about one of its vertical sides. The coil is in a radial horizontal field of 90 G (radial here means the field liners are in the plane of the coil for any rotation). What is the torsional constant of the hair spring connected to the coil if a current of 2.0 mA produces an angular deflection of 18^@ ?