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Four point charges –Q, –q, 2q and 2Q are placed, one at each corner of the square. The relation between Q and q for which the potential at the centre of the square is zero is:
- Q = –q
- Q = –1 / q
- Q = q
- Q = 1 / q
Correct answer: Q = –q
Solution
The potential at the center of the square is the algebraic sum of the potentials due to all four charges. For the potential to be zero, the contributions from the charges must cancel out. Solving the equation for symmetry and charge magnitudes, we find Q = -q.
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