Electrostatic Potential Energy

In the first configuration (1) as shown in the figure, four identical charges are kept at the corners A, B, C and D of square of side length ' '. In the second configuration (2), the same charges are shifted to mid points and , of the square. If , the difference between the potential energies of configuration (2) and (1) is given by:
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Answer: (d)
- Config (1): 4 sides of length and 2 diagonals :
- Mid-points form a square of side with diagonal .
- Config (2):
- , answer (d).