Figure shows in cross section a wall consisting of four layers with thermal conductivities `K_(1) = 0.06 W // mK, K_(3) = 0.04 W// mK and K_(4) = 0.10 W// mK`. The layer thickness are `L_(1) = 1.5 cm, L_(3) = 2.8 cm and L_(4) = 3.5 cm`. The temperature of interfaces is as shown in figure. energy transfer through the wall is in steady state. the temperature of the interface between layer `3 and 4` is:

Options

A. `-1^(@)C`
B. `-3^(@)C`
C. `2^(@)C`
D. `0^(@)C`

Answer

B

Explanation

In steady state `(DeltaQ)/(DeltaT):|_(layer1)`=`(DeltaQ)/(Deltat):|_(layer4)`
`rArr (0.06 xx A xx (30 - 25))/(1.5 xx 10^(-2)) = (0.10 xx A xx DeltaT)/(3.5 xx 10^(-2))`
`rArr DeltaT = 7^(@)C`
`T_(3) = (-10+7)^(@)C =- 3^(@)C`