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Question:

A system of three charges are placed as shown in the figure: If D>>d, the potential energy of the system is best given by

14πε0[−q²d−qQd/D²]

14πε0[−q²d−qQd/2D²]

14πε0[+q²d+2qQd/D²]

14πε0[−q²d+qQd/D²]

Solution:

Correct option is D. 14πε0[−q²d−qQd/D²]
Utotal=Uselfofdipole+Uinteraction=−kq²d−(kQq/D²)d=−k[+q²d+qQd/D²]