Two conducing concentric hollow spheres of radii a and 2a respectively are shown in the diagram.  The inner shell has net charge Q on its surface.  The outer shell is neutral.  If the outer shell is connected to the earth the heat generated through the connecting wire is
 

• A

  Zero

• B

  $\frac{1}{4\mathrm{\pi }{\in }_0}.\frac{{\mathrm{Q}}^2}{2\mathrm{a}}$

• C

  $\frac{1}{4\mathrm{\pi }{\in }_0}.\frac{{\mathrm{Q}}^2}{4\mathrm{a}}$

• D

  $\frac{1}{4\mathrm{\pi }{\in }_0}.\frac{{\mathrm{Q}}^2}{\mathrm{a}}$