Two rods $A$ and $B$ of different materials are welded together as shown in figure.Their thermal conductivities are $K_1$ and $K_2$ The thermal conductivity of the composite rod will be
$\frac{{3{K_1}{K_2}}}{2}$
$\frac{{{K_1} + {K_2}}}{3}$
$\;\frac{{{K_1}{K_2}}}{{3({K_1} + {K_2})}}$
$\;\frac{{{K_1} + {K_2}}}{2}$
Two thin blankets keep more hotness than one blanket of thickness equal to these two. The reason is
For cooking the food, which of the following type of utensil is most suitable
Assertion : The equivalent thermal conductivity of two plates of same thickness in contact is less than the smaller value of thermal conductivity.
Reason : For two plates of equal thickness in contact the equivalent thermal conductivity is given by : $\frac{1}{K} = \frac{1}{{{K_1}}} + \frac{1}{{{K_2}}}$
Figure shows three different arrangements of materials $1, 2$ and $3$ to form a wall. Thermal conductivities are $k_1 > k_2 > k_3$ . The left side of the wall is $20\,^oC$ higher than the right side. Temperature difference $\Delta T$ across the material $1$ has following relation in three cases
On a cold morning, a metal surface will feel colder to touch than a wooden surface because