Steady-heat conduction occurs through a homogeneous, isotropic plane wall of thickness
. The thermal conductivity of the wall is a linear function of temperature. The external surfaces of the wall are maintained at constant temperatures t1 and t2 respectively. Assuming temperature to vary only in the direction normal to the wall derive an expression for the temperature at any point in the wall in terms of the wall temperatures, wall thickness and the distance x measured from the high temperature surface in the direction of decreasing temperature.