Question

$1.56 × 10^5$ J of heat is conducted through a $2\, m^2$ wall of $12\, cm$ thick in one hour. Temperature difference between the two sides of the wall is $20^{\circ} C$. The thermal conductivity of the material of the wall is (in $W \,m^{-1}\, K^{-1}$)

• A. $0.11$
• B. $0.13$
• C. $0.15$
• D. $1.2$

Answer 1

Answer: (B)

Given that $1.56 \times 10^{5} J$ of heat is conducted through a $2\, m ^{2}$ wall having a thickness of $12\, cm$ in a time interval of $1 h$.
Hence, we have $\frac{d Q}{d t}=\frac{K A \Delta T}{x}$
Thus, we get $\frac{1.56 \times 10^{5}}{1 \times 60 \times 60}$
$=\frac{K \times 2 \times 20}{12 \times 10^{-2}}$
So, $K=\frac{1.56 \times 10^{5} \times 12 \times 10^{-2}}{1 \times 60 \times 60 \times 2 \times 20}$
$=\frac{1.56}{12}=0.13$