EMinMatter03.pptVIP

EM Fields in Matter * YUNNAN NORMAL UNIVERSITY College of Physics and Electronic information YUNNAN NORMAL UNIVERSITY College of Physics and Electronic information The external electric field will align the dipole moments of the molecules inside the matter. Electric Field in Matter E Due to the thermal fluctuation, the microstructure of the dipoles is impossible to know. But we only concern about the macro properties (the average) of the matter. YUNNAN NORMAL UNIVERSITY College of Physics and Electronic information E0 - - - - - - + + + + + E’ The effect of an external electric field on the matter is to produce resisting electric field The total electric field inside the matter is is generated by all the dipole moments; it is an average effect. YUNNAN NORMAL UNIVERSITY College of Physics and Electronic information E One average quantity is suitable to describe the polarized matter: polarization is very small, but at least contains hundreds of dipoles YUNNAN NORMAL UNIVERSITY College of Physics and Electronic information Why polarization? Polarization measures how much the matter is affected (polarized) by electric field. It is determined by the external field and the property of the matter. The individual dipole moments in the matter are intractable. But it is possible to investigate the statistical average of them, which determines the macro-property of the matter YUNNAN NORMAL UNIVERSITY College of Physics and Electronic information Bound charges The potential of a dipole moment origin where The average potential of all dipoles inside the matter: Note: the average potential is related to polarization which itself is an average quantity. YUNNAN NORMAL UNIVERSITY College of Physics and Electronic information The potential due to the dipoles is actually generated by the bound charges. We can find these bound charges through the potential. Use this relation YUNNAN NORMAL UNIVERSITY College of Physics and Electronic information Integration by parts Accordi