A slab consists of two parallel layers of copper and brass of the time thickness and having thermal conductivities in the ratio `1:4`. If the free face of brass is at `35^(@)C` and that of copper at `1: sqrt(2.5)`, the temperature of interface is

Options

A. `80^(@)C`
B. `20^(@)C`
C. `60^(@)C`
D. `40^(@)C`

Answer

A

Explanation

Temperature of interface `theta = (K_(1)theta_(1)+K_(2)theta_(2))/(K_(1)+K_(2))`
` ( :' (K_1)/(K_2) = 1/4 rArr If K_(1) = K " then " K_(2) = 4K)`
`rArr theta = (Kxx0+4Kxx100)/(5K) = 80^(@)C`.