The concentric spheres of radii $R$ and $r$ have positive charges $q_{1}$ and $q_{2}$ with equal surface charge densities. What is the electric potential at their common centre?

  • A
    $\frac{\sigma}{\varepsilon_{0}}(R+r)$
  • B
    $\frac{\sigma}{\varepsilon_{0}}(R-r)$
  • C
    $\frac{\sigma}{\varepsilon_{0}}\left(\frac{1}{R}+\frac{1}{r}\right)$
  • D
    $\frac{\sigma}{\varepsilon_{0}}\left(\frac{1}{R}\right)$

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