The temperature of the two outer surfaces of a composite slab, consisting of two materails having coefficients of two materails having coefficients of termal conductivity K and 2K and thickness x and 4x, respectively, are `T_2 and T_1(T_1gtT_1)`. The rate of heat transfer through the slab, in a steady state is `((A(T_2-T_1)K)/2)f`, with f equal to

Options

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

Answer

D

Explanation

(d) The thermal resistance
`x/(KA)+(4x)/(2KA)=(3x)/(KA)`
`:. (dQ)/(dt)=(DeltaT)/((3x)/(KA))=((T_2-T_1)KA)/(3x)=1/3{(A(T_2-T_1)K)/x}`
`:. f=1/3`