Electric Dipole in an External Electric Field

" When you look at yourself from a universal standpoint, something inside always reminds or informs you that there are bigger and better things to worry about."
Albert Einstein

We have already considered the electric field created by an electric dipole. Now we consider the behavior of an electric dipole placed in a uniform (constant) electric field.

elec dip in external field

Note that since the force on each of the charges are equal in magnitude but opposite in direction there is no net force on the dipole.

However, since the two forces are not concurrent, there is a non-zero torque about the center of the dipole given by,

Using the definition of the work done by a torque (rotational force), it can be shown that the electrical potential energy stored by a dipole in an external field is given by,

A dipole placed in a uniform electric field will rotate until it is aligned "-" to "+" along the field - this is the lowest energy configuration.

If the external field is not uniform, the net force will not be zero.

What is a quantum particle? The dreams that stuff is made of!

Dr. C. L. Davis
Physics Department
University of Louisville
email: c.l.davis@louisville.edu