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A charge of $+Q$ is placed on the innermost and outermost of three concentric conducting spherical shells. The middle shell is grounded via a thin wire that passes through an insulated hole in the outer shell and hence has a potential (relative to $\infty$) of 0.

a) Find the charge $Q_s$ on the middle shell in terms of $k$, $Q$, and the given radii $a$, $b$ and $c$.

b) Find the potential at all points in space (in each region where there is a distinct field). You may express your answers algebraically in terms of $Q_s$ to make life a bit simpler (and independent of your answer to part a).