Since
the field is radial by design, we have taken sin q = 1 in
the above expression for the torque The magnetic
torque NIAB tends to rotate the coil A spring Sp
provides a counter torque kf that balances the
magnetic torque NIAB; resulting in a steady angular
deflection f In equilibrium
kf = NI AB
where k is the torsional constant of the spring; i