Two concentric conducting shells of radius a and b (> a) carry charges Q and -2Q, respectively. The correct variation of electric intensity E as a function of r is given by

The inner face of the outer shell has the charge -Q and its outer face also has the charge -Q.

The final charge distribution on each face of shells is shown in figure. The expression for electric field is

$\mathrm{givenby} \mathrm{E}=\frac{\mathrm{kQ}}{{\mathrm{r}}^2} \mathrm{for} \mathrm{a}<\mathrm{r}<\mathrm{b} (\mathrm{radiallyoutwards})$

$\text{ And }\mathrm{E}=-\frac{\mathrm{kQ}}{{\mathrm{r}}^2}\text{ for }\mathrm{r}>\mathrm{b} \text{ (radially inwards) }$

Note that the field in the outward direction is assumed to be positive.