question_answer

A composite plane wall is made up of two different materials of the same thickness and having thermal conductivities of \[{{k}_{1}}\] and \[{{k}_{2}}\] respectively. The equivalent thermal conductivity of the slab is:

A) \[{{k}_{1}}+{{k}_{2}}\]                     

B) \[{{k}_{1}}{{k}_{2}}\]

C) \[\frac{{{k}_{1}}+{{k}_{2}}}{{{k}_{1}}{{k}_{2}}}\]             

D) \[\frac{2{{k}_{1}}{{k}_{2}}}{{{k}_{1}}+{{k}_{2}}}\]