The torque of a
force about an axis is measured by the product of the force and the perpendicular
distance of its line of action from the axis of rotation.
Ʈ
= r ×
F
This applies to rotatory motion. Here an electric
dipole also experiences torque in the uniform electric field. An electric dipole
means two equal and opposite charges separated by a small distance constitute
an electric dipole. For instance, CO is a dipole molecule. Suppose an electric
dipole of dipole moment is placed in the uniform electric field whose field lines are
equally spaced and point in the same direction.
The charge +q experienced a force +qE in the direction of the
field and charge –q experienced a force –qE in a direction opposite to the
field. Since the external field E is uniform the force acting on the dipole is
zero. Already the charges experienced force between them and the external
uniform field is also acting on the charges, so that both forces acting at different points will constitute a couple and the dipole experienced a torque. In
case the electric field is not uniform, the force experienced by +q is
different from that experienced by –q. In addition to the torque, there will be a net force acting on the dipole.
Tags
physics