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 `(Delta Q)/(DeltaT)|_("layer" 1)` = `(Delta Q)/(Delta t)|_("layer" 4)`
`rArr (0.06xxAxx(30-25))/(1.5xx10^(-2)) = (0.10xxAxxDelta T)/(3.5xx10^(-2))`
`rArr Delta T = 7^(@)C`
`T_(3)=(-10+7)^(@)C = -(3)^(@)C`.