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Lecture_04 - Polarization of Atoms Force due to E created...

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+ E Force due to E created by positive charge shifts electron cloud and nucleus in opposite directions: electric dipole . An atom is said to be polarized when its electron cloud has been shifted by the influence of an external charge so that the electron cloud is not centered on the nucleus . Polarization of Atoms it is not a permanent dipole • an induced dipole is created when a neutral object is polarized by an applied electric field An applied electric field creates induced dipoles: α - “ polarizability” of a material Note the “p” direction! p = qs = α E
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r r q E ˆ 4 1 2 1 0 1 πε = r r q p ˆ 4 1 2 1 0 α πε = r r q E ˆ 2 4 1 5 1 2 0 2 α πε = r r q F ˆ 2 4 1 5 2 1 2 0 1 α πε = 1) 2) 3) 4) r r q F ˆ 2 4 1 5 2 1 2 0 2 α πε = 5) Neutral atoms are attracted by charges! Interaction strength ~ 1/r 5 A Neutral Atom and a Point Charge
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Interaction of Charged Objects Attraction: can happen also for like-charged objects! Repulsion: can happen only for like-charged objects! r r q N r q q F ˆ 2 4 1 4 1 5 2 1 2 0 2 2 1 0 = α πε πε Intervening matter does not “block” the E field The resulting field is a superposition of two fields: Field of the other charge plus the field of induced dipoles.
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Clicker Question The force of one of the permanent dipoles on the other is: A)Attractive B)Repulsive
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