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

Options

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

Answer

B

Explanation

(2) `R_(A) = (L)/(2KA) = R, R_(B) = (L)/(KA) = 2R`
`R_(eq) = R_(A) + R_(B) = 3R`
In series heat curretn is same
`i = (theta_(1) - theta)/(R_(A)) = (theta_(1) - theta_(2))/(R_(eq))`
`(theta_(1) - theta)/(R ) = (36)/(3R)`
`theta_(1) - theta = 12^(@)C`
Temperature difference between two layers of `A = 12^(@)C`