When a molecule of a dielectric material is placed in an electric field, the molecule acquires an electric dipole moment. Why?
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2 Answers
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An atom may be neutral as a whole but its parts aren't. The electric field applies opposite forces to the negatively-charged electron cloud and the positively-charged nucleus, resulting in a net separation of charge. This results in a dipole moment.
This is covered in section 4.1.2 of Griffiths' Introduction to Electrodynamics.
answered Apr 29 at 21:08
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The molecule doesn't "acquire" a dipole moment from the electric field. The electric dipole moment is a measure of the separation of positive and negative charges within a system, i.e., a measure of the system's overall polarity. See https://en.wikipedia.org/wiki/Electric_dipole_moment#Energy_and_torque
That said, an object with an electric dipole moment acquires a torque when placed in an external electric field equal to the cross product of the dipole moment and the electric field.
Hope this helps.
