Electrostatics

For a charged spherical ball, electrostatic potential inside the ball varies with \(r\) as \(\mathrm{V}=2ar^2+b\).

Here, \(a\) and \(b\) are constant and r is the distance from the center. The volume charge density inside the ball is \(-\lambda a\varepsilon\). The value of \(\lambda\) is ____________.

\(\varepsilon\) = permittivity of the medium