For a charged spherical ball, electrostatic potential inside the ball varies with $r$ as $V =2 ar ^2+ b$. 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 medium.
A$11$
B$12$
C$6$
D$3$
JEE MAIN 2023, Diffcult
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B$12$
b $E =-\frac{ dV }{ dr }=-4 ar \equiv \frac{\rho r }{3 \varepsilon_0} \text { (compare) }$
Result inside uniformly charged solid sphere.
$\rho=-12 a \varepsilon_0$
$\lambda=12$
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