This is because the perpendicular distance
between the forces of the couple has decreased Figure 4 19(b) is a view
of the arrangement from the AD end and it illustrates these two forces
constituting a couple The magnitude of the torque on the loop is,
1
2
sin
sin
2
2
a
a
F
F
τ
θ
θ
=
+
= I ab B sin q
   = I A B sin q
(4