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. `28^(@)C`
B. `14^(@)C`
C. `7^(@)C`
D. `5^(@)C`

Answer

D

Explanation

In the state, rate of heat across each layer of the wall is the same.
`(K_(A)A(DeltaT))/(10) = (K_(B)A(35-DeltaT))/(20)`
Using `K_(A) = 3K_(B)`, solving , `Delta T = 5^(@)C`