The electrostatic potential inside a charged spherical ball is given by : $V = b -ar^2$, where  $r$ is the distance from the centre ; $a$ and $b$ are constants. Then, the charge density inside the ball is :
  • A$24\pi \,a{\varepsilon _0}r$
  • B$6\,a{\varepsilon _0}r$
  • C$24\pi \,a{\varepsilon _0}$
  • D$6\,a{\varepsilon _0}$
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