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

The two slabs are in series
`thereforek_(eq)=(X+4X)/((X)/(K)+(4X)/(2K))=(5K)/(3)rArr"Heat flow rate"=((5K)/(3))(A)/((5X))(T_(2)-T_(1))rArrH=[(kA)/(X)(T_(2)-T_(1))]xx(1)/(3)thereforef=(1)/(3)`