Two metal rods are fixed end to end between two rigid supports as shown in figure. Each rod is of length `l` and area of cross-section is `A`. When the systeam is heated up,datermine the condition when the juncation between rods does not shift ? (`Y_(1)` and `Y_(2)` are Young's modulus of materials of rods, `alpha_(1)` and `alpha_(2)` are coefficients of linear expansion)