JEE Main 2020 — Thermal Properties of Matter Question with Solution

Three rods of identical cross-section and length are made of three different materials of thermal conductivity $K_1, K_2$ and $K_3$, respectively. They are joined together at their ends to make a long rod (see figure). One end of the long rod is maintained at $100°\mathrm{C}$ and the other at $0°\mathrm{C}$ (see figure). If the joints of the rod are at $70°\mathrm{C}$ and $20°\mathrm{C}$ in steady and there is no loss of energy from the surface of the rod, the correct relationship between $K_1\mathit{,}\mathit{ }{K}_{\mathit{2}}$ and $K_3$ is :