A solid sphere of radius `R` has a spherical cavity of radius `r` as shown in the figure. If the volume charge density `sigma` is uniformly distributed over the whole volume of the sphere, then electric field strength at the centre of the sphere will be

Options

A. `(R^(3)sigma)/(2piepsilon_(0)(R-r)^(2))`
B. `(Rsigma)/(3piepsilon_(0))`
C. `(1)/(3epsilon_(0))(r^(3)sigma)/((R-r)^(2))`
D. `(rsigma)/(3epsilon_(0)(R-r)^(2))`

Explanation

`E=(1)/(4piepsilon_(0))((4)/(3)pir^(3)sigma)/((R-r)^(2))`
`=(1)/(3epsilon_(0))(r^(3)sigma)/((R-r)^(2))`