Potential at center of square (side a) with charges +q, -q, +q, -q at corners (alternating):
A0
Bkq/a
C2kq/a
D-kq/a
Answer & Solution
Correct answer: A. 0
Each corner is at distance a/√2 from center. Total V = (kq/(a/√2))(+1 -1 +1 -1) = 0. The alternating signs cancel exactly.
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