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Unformatted text preview: Lecture 32 Electric field lines. The electric dipole. Example: The electric dipole +- d + Q-Q Definition: Electric dipole moment p Q d = G G Direction: From to + p G What happens to a dipole in an external electric field? An electric dipole is placed in a uniform electric field E ext . +- F = QE ext F = QE ext E ext ext sin into the page net d Q E = ext net p E = G G G The CM of the dipole does not move but the dipole rotates. d net F = E ext p +- When the dipole rotates an angle d , the work done by the electric field is: dW d = For a finite displacement: = = + = ext ext sin (cos cos ) f i i f W p E d p E U E ext ext sin into the page pE = p ext sin p E d = d is out of the page ext ext cos U p E p E = = G G Dipole in a uniform electric field: ext ext net p E U p E = = G G G G G ext ext sin cos net pE U p E = = G E ext- + p E ext- + p E ext- + p ext MAX 180 U pE U = = = =...
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- Fall '06