State and explain the laws of thermal conductivity and hence mention the SI unit of coefficient of thermal conductivity.

Explanation

The quantity of heat conducted during the steady state is directly proportional to the,
(i) Area of cross-section of a conductor.
(ii) Temperarture difference between the two points or ends `(theta_1-theta_2)`
(iii) Time of passage of heat (t) and inversely proportional to the thickness or distance between the two ends of the conductor (d)
i.e, `Q=(KA(theta_1-theta_2)/(d))`
where 'K' is thermal conductivity of the material of the conductor.