What is the electric potential energy in II?

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1 Answer
A08
Jul 30, 2018

Electric potential energy between two charges is given by the following expression

#U=1/(4piepsilon)(q_1q_2)/R_12#

For charges in figure I

#W=1/(4piepsilon)((+3q)xx(+2q))/d#
#=>W=1/(4piepsilon)(6q^2)/d# ........(1)

If there are more than two charges in the system, then electric potential energy is calculated for each pair and total energy is found by adding all algebraically.

Therefore, for charges as in figure II

#U_(II)=1/(4piepsilon)((+3q)(+q))/d+1/(4piepsilon)((+q)(-q))/d+1/(4piepsilon)((+3q)(-q))/d#
#=>U_(II)=1/(4piepsilon)[(3q^2)/d-(q^2)/d-(3q^2)/d]#
#=>U_(II)=-1/(4piepsilon)(q^2)/d#

Using (1) we get

#=>U_(II)=-W/6#

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