Question

Two metallic blocks M1 and M2 of the same cross-section area are connected (as shown in the figure). If the thermal conductivity of M2 is K then the thermal conductivity of M1 will be : [Assume steady state heat conduction]

• A. 10K
• B. 8K
• C. 12.5K
• D. 2K

Answer 1

Answer: (B)

8K

Answer 2

Thermal current is same so
$\frac{dQ}{dt}$=$\frac{ΔT_1}{\frac{l_1}{K_1}}$A=$\frac{ΔT_2}{\frac{l_2}{K_2}}$A
or, 2$\frac{20}{16}$×K'=$\frac{80}{8}$×K
⇒K'=8K
The correct option is (B) : 8K