Experimental Set-up

The Searle's apparatus to measure the thermal conductivity of a solid is shown in Figure. The solid is taken in the form of a cylindrical rod A B. One end A of the rod goes into a steam chamber through which steam is passed from a boiler. A copper tube is coiled around the other end B of the rod. This end B is cooled by circulating a steady flow of water maintained in the copper tube by constant water level tank. The flow of water is adjusted using pinch cork such that water comes drop by drop from the exit side. Water enters the tube at the end away from the steam chamber and it leaves at the end nearer to it. Thermometers T3 and T4 are provided to measure the temperatures of the outgoing and incoming water. Two holes are drilled in the rod and the temperature of the rod is also measured at these places with the help of thermometers T1 and T2. The whole apparatus is covered properly with layers of an insulating material like wool or felt, so as to prevent any loss of heat from the sides. Steam is passed into the steam chamber and a stream of water is maintained. The temperatures of all the four thermometers rise initially and ultimately become constant when the steady state is reached. The readings θ1, θ2 , θ3 and θ4 are noted in steady state.