Heat and Thermodynamics

11.5 Forbes’ Method

It is one of the earliest methods for determination of thermal conductivity of a substance. The experiment is a tedious one. Forbes performed the experiment in 1864.

The principle of the method is that at the steady state, the quantity of heat passing through any section of a bar will be equal to the quantity of heat lost by radiation by the remaining part of the bar. Let l be the length, A be the area of cross section, ρ be the density, c be the specific heat and K be the thermal conductivity of the material of the bar. We consider a section of the bar at a distance x = x₁ from the hot end of the bar; then according to the theory, the quantity of heat passing through the section at x = x₁ per second

 

 

At the steady state, ...