Question

A parallel-sided slab is made of two different materials. The upper half of the slab is made of material X, of thermal conductivity l; the lower half is made of material Y, of thermal conductivity 2l . In the steady state, the left hand face of the composite slab is at a higher, uniform temperature than the right-hand face, What fraction of the total heat flow through the slab passes through material X ?

• A. $\frac{1}{4}$
• B. $\frac{1}{3}$
• C. $\frac{1}{2}$
• D. $\frac{2}{3}$

Answer 1

Answer: (B)

$\frac{1}{3}$

Answer 2

t = $\frac{(T_{1}–T_{2})3\lambda A}{L}$

t₁ = $\frac{(T_{1}–T_{2})\lambda A}{L}$

$\frac{\tau_{}}{\tau_{1}}$ = 3 Ž t₁ = t/3