Chapter 24, Problem 26P

The heat flux q is the quantity of heat flowing through a unit area of a material per unit time. It can be computed with Fourier's law,

$J=-k\frac{dT}{dx}$

Where J has units of $\text{J}/{\text{m}}^2\text{/s or }\text{W}/{\text{m}}^2$ and k is a coefficient of thermal conductivity that parameterizes the heat-conducting properties of the material and has units of $\text{W}/\left(°\text{C}\cdot \text{m}\right).T=\text{temperature }\left(°\text{C}\right);\text{ and }x=$ distance (m) along the path of heat flow. Fourier's law is used routinely by architectural engineers to determine heat flow through walls. The following temperatures are measuredfrom the surface $\left(x=0\right)$ into a stone wall:

x, cm	0	0.08	0.16
T, $°\text{C}$	20	17	15

If the flux at $x=0\text{is 60 }\text{W}/{\text{m}}^2$, compute k,