Diagram Deducing electric field expression (i) To the left of first sheet (ii) To the right of second sheet (iii) Between the two sheets Diagram : Electric field in the region left of first sheet$E_I=E_1+E_2$$E_I=\frac{\sigma}{\varepsilon_0}-\frac{\sigma}{2\varepsilon_0}$$E_I=+\frac{\sigma}{2\varepsilon_0}$ It is towards right, Electric field in the region to the right of second sheet $E_{II}=\frac{\sigma}{2\varepsilon_0}-\frac{\sigma}{\varepsilon_0}$ $E_{II}=-\frac{\sigma}{2\varepsilon_0}$ It is towards left, Electric field between the two sheets $E_{\text{III}}=E_I+E_{\text{II}}$ $E_{\text{III}}=\frac{\sigma}{\varepsilon_0}+\frac{\sigma}{2\varepsilon_0}$ $E_{\text{III}}=\frac{3\sigma}{2\varepsilon_0}$ Electric field is towards the right. OR Diagram Finding the surface charge density in the inner and outer surface of the shell Electric field in the cavity Diagram: The surface charge density on inner surface of the shell is $\sigma_1=-\frac{q}{4\pi r_1^2}$ The surface charge density on outer shell is $\sigma_2=-\frac{Q+q}{4\pi r_2^2}$ (b) Consider a Gaussian surface inside the shell, net flux is zero since $q_{\text{net}}=0$. According to Gauss's law it is independent of shape and size of shell.