10 A planar loop carrying a current I, having N closely wound turns, and
an area A possesses a magnetic moment m where,
m = N I A
and the direction of m is given by the right-hand thumb rule : curl
the palm of your right hand along the loop with the fingers pointing
in the direction of the current The thumb sticking out gives the
direction of m (and A)
When this loop is placed in a uniform magnetic field B, the force F on
it is:  F = 0
And the torque on it is,
t = m × B
In a moving coil galvanometer, this torque is balanced by a counter-
torque due to a spring, yielding
kf = NI AB
where f  is the equilibrium deflection and k the torsion constant of
the spring 11