Two cylindrical rods, of different material, are joined as shown. The rods have same cross section `(A)` and their electrical resistivities are `rho_(1) and rho_(2)`. When a current `I` is passed through the rods, a charge `(Q)` gets piled up at the junction boundary. Assuming the current density to be uniform throughout the cross section, calculate `Q`.

Answer

`Q=(rho_(2)-rho_(1))in_(0)I`
Q is negative if `rho_(a) gt rho_(2)`]