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Two thin wire rings each having a radius $R$ are placed at a distance $d$ apart with their axes coinciding. The charges on the two rings are $ + q$ and $ - q$. The potential difference between the centres of the two rings is
  • A
    Zero
  • B$\frac{Q}{{4\pi {\varepsilon _0}}}\,\left[ {\frac{1}{R} - \frac{1}{{\sqrt {{R^2} + {d^2}} }}} \right]$
  • C$QR/4\pi {\varepsilon _0}{d^2}$
  • D$\frac{Q}{{2\pi {\varepsilon _0}}}\left[ {\frac{1}{R} - \frac{1}{{\sqrt {{R^2} + {d^2}} }}} \right]$
AIEEE 2005, Diffcult
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