Question

Lee's disc method of determine bad conductor

Answer 1

The Lee’s Disc experiment determines an approximate value for the thermal conductivity k of a poor conductor like glass, cardboard, etc. The procedure is to place a disc made of the poor conductor, radius r and thickness x, between a steam chamber and two good conductivity metal discs (of the same metal) and allow the setup to come to equilibrium, so that the heat lost by the lower disc to convection is the same as the heat flow through the poorly conducting disc. The upper disc temperature T2 and the lower disc temperature T1 are recorded. The poor conductor is removed and the lower metal disc is allowed to heat up to the upper disc temperature T2. Finally, the steam chamber and upper disc are removed and replaced by a disc made of a good insulator. The metal disc is then allowed to cool through T1 < T2 and toward room temperature T0. The temperature of the metal disc is recorded as it cools so a cooling curve can be plotted. Then the slope s1 =ΔT/Δt  of the cooling curve is measured graphically where the curve passes through temperature T1.