Ans: Statement of Fourier's law of heat conduction:

*"The rate of heat conduction through a plane wall is proportional to the temperature difference across the layer and heat transfer area, but is inversely proportional to the thickness of the layer"*

Fourier's law in differential form is given by,

Where,

k = thermal conductivity in W/m^2.K

A = area normal to the heat flow in m^2

dT/dx = temperature gradient