The temperature of the two outer surfaces of a composite slab consisting of two materials having coefficient of thermal conductivity K and 2K and thickness x and 4x respectively are `T_2` and `T_1(T_2gtT_1)`. The rate of heat transfer through the slab in steady state is `((AK(T_2 -T_1))/x)f`. where, f is equal to
.

Options

A. 1
B. `1//2`
C. `2//3`
D. `1//3`

Answer

D

Explanation

`R_("net") = R_1 + R_2 = (X/(KA)) + (4X)/(2KA) = (3X)/(KA)`
Now, `H = (dQ)/(dt) = (TD)/(R_("net"))`
`=((T_2 -T_1))/((3X//KA)) = [(KA(T_2-T_1))/x] (1/3)`
`:. f = 1/3` .