Define thermal conductivity. Write its SI unit.

Explanation

If the area of cross section`=1m^2`, temperature difference=1K, Passage of time=1s and distance between the two points is separated by 1m then Q=K
Hence thermal conductivity is numerically equal to the amount of heat conducted across a conductor of length lm, whose ends are maintained with a temperature difference of 1K for a time period of one second and having a Qnit area of cross-section.
The SI unit of thermal conductivity is `Wm^(-1)K^(-1)`