Two rods \(A\) and \(B\) of different materials are welded together as shown in the figure. Their thermal conductivities are \(K_1\) and \(K_2.\) The thermal conductivity of the composite rod will be:
1. | \(\frac{3(K_1+K_2)}{2}\) | 2. | \(K_1+K_2\) |
3. | \(2(K_1+K_2)\) | 4. | \(\frac{(K_1+K_2)}{2}\) |