Final answer:
An electric dipole in a uniform electric field experiences no net force because the equal and opposite forces on the two charges of the dipole cancel out, although a net torque may exist.
Step-by-step explanation:
To show that an electric dipole held in a uniform electric field experiences no net force, we can consider the dipole as two point charges of equal magnitude but opposite sign, +2q and -2q, separated by a distance d. In a uniform electric field, these charges experience forces of equal magnitude but in opposite directions. Since the electric field is uniform, the magnitudes of these forces are the same, hence they cancel out, leaving the dipole with a net force of zero. However, there will be a net torque on the dipole, which tends to align the dipole with the direction of the field.
Despite the presence of a third charge, if the scenario kept the electric field uniform and the dipole moment correctly aligned, the previous analysis holds true with zero net force on the dipole.
The net electric field can be considered as the sum of the fields due to the dipole's charges and the external field. Additionally, the phenomenon that dipoles in a dielectric align with an external electric field, which does not lead to a net force within the dielectric, supports this conclusion from a molecular perspective.