A wall has two layers A and B each made of different materials. The layer A is 10cm thick and B is 20 cm thick. The thermal conductivity of A is thrice that of B. Under thermal equilibrium temperature difference across the wall is `35^@C`. The difference of temperature across the layer A is

Options

A. `20^(@)C`
B. `10^(@)C`
C. `15^(@)C`
D. `5^(@)C`

Answer

D

Explanation

`R_(A) = (10)/(3KA)``(therefore R=l/(KA))`

`R_(B) = (20)/(KA) rArr R_(A)/R_(B)=1/6`
so let `R_(A)`=R then `R_(B)` = `1/6`
So let `R_(A)`=R, then `R_(B)` = `5/R`
Now temperature difference across A
`=H xx R_(A)=5/R xx R= 5^(@)C`