Where do we use an electric dipole or what is the use/significance of the dipole moment?
An electrical dipole is a couple of two electrical charges identical in amplitude but opposite in sign, say +q and -q (q>0), separated by a distance d.
This is for istance the electrical model of polar molecules.
see also
http://en.wikipedia.org/wiki/Electric_dipole_moment
If you calculate potential due to a dipole at a distance which is
large compared to d, then leading term in the potential cancels
due to the presence of both +q and -q, but there is a sub leading
term in the expression for potential proportional to 1/r^2. Therefore
for a single charge electric field falls as 1/r^2 for dipole potential
falls as 1/r^2. Dipole potential, thus, falls off quickly and corresponding
electric field falls of as 1/r^3, which is even faster. Dipole interaction,
consequently, is a short distance phenomenon. This phenomenon
is manifested in nature at many places. A prominent place being
the interaction of two atoms, where each atom is a dipole and the
mutual interaction is a dipole-dipole interaction. This interaction is
thus very fundamental to our own existence.
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