A wall has two layers A and B, each made of different material. Both the layers have the same thickness. The thermal conductivity of the material of A is twice that of B . Under thermal equilibrium, the temperature difference across the wall is `36^@C.` The temperature difference across the layer A is

Options

A. `6^(@)`C
B. `12^(@)`C
C. `24^(@)`C
D. `18^(@)`C

Answer

B

Explanation

`because K_(A) =2K_(B)`
`therefore R_(A) = R_(B)/2 (R= 1/(KA))`
Suppose, `R_(A) = R, then R_(B) = 2R`
Heat current , `H = 36/(R+2R) = 36/(3R)= 12/R`
`therefore` Temperature difference across A `= HxxR_(A) = 12/R XXR = 12^(@)C`