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. `18^@C`
D. `24^@C`

Answer

B

Explanation

`H=(2kA(T_(1)-T))/(L)=(kA(T-T_(2)))/(L)`

`implies 2T_(1)-3T=T_(1)-T_(2)`
`implies T_(1)-T=(T_(1)-T_(2))/(3)`
`=(36)/(3)=12^(@)C`