Correct Answer - Option 2 : 2 ∶ 1
CONCEPT:
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Thermal conductivity: It is defined as the property of a given material to transfer heat energy.
It is given by:
\(k = \frac{QL}{AΔ T}\)
Where k is the thermal conductivity (Wm-1K-1), Q is the amount of heat transferred through the material (W), L is the length between two points of the material (m), A is the cross-sectional area perpendicular to heat flow (m2), and ΔT is the change in temperature (K).
CALCULATIONS:
Given that, T1 = 25 min, T2 = 50 min
As from the above formula
\(k = \frac{QL}{AΔ T}\)
Here, the material is different and the quantity is the same
k α 1/T and all other parameters are constant
\(\frac{k_1}{k_2}=\frac{\Delta T_2}{\Delta T_1}=\frac{50}{25}=\frac{2}{1}\)
So the ratio of thermal conductivity is 2:1