The radii of two concentric circles spherical conducting shells are r1 and r2 (r1<r2) .The change on the outer shell is q. The charge on the inner shell which is connected to the earth is
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The charge on the outer one will create a potential V=kq/r2 on its surface and inside. To keep its zero potential the inner sphere has to get a charge -(r1.q/r2) which will create a potential -V on it.