Two rods of same length and cross section are joined along the length. Thermal conductivities of first and second rod are ${K_1}\,\,{\rm{and}}\,\,{K_2}$. The temperature of the free ends of the first and second rods are maintained at ${\theta _1}\,\,{\rm{and }}{\theta _2}$ respectively. The temperature of the common junction is
$\frac{{{\theta _1} + {\theta _2}}}{2}$
$\frac{{{K_2}{K_2}}}{{{K_1} + {K_2}}}({\theta _1} + {\theta _2})$
$\frac{{{K_1}{\theta _1} + {K_2}{\theta _2}}}{{{K_1} + {K_2}}}$
$\frac{{{K_2}{\theta _1} + {K_1}{\theta _2}}}{{{K_1} + {K_2}}}$
A wall consists of alternating blocks of length $d$ and coefficient of thermal conductivity $K_{1}$ and $K_{2}$ respectively as shown in figure. The cross sectional area of the blocks are the same. The equivalent coefficient of thermal conductivity of the wall between left and right is
A thin paper cup filled with water does not catch fire when placed over a flame. This is because
rod of $40\, cm$ in length and temperature difference of ${80^o}C$ at its two ends. $A$ nother rod $B$ of length $60\, cm$ and of temperature difference ${90^o}C$, having the same area of cross-section. If the rate of flow of heat is the same, then the ratio of their thermal conductivities will be
Snow is more heat insulating than ice, because
The heat is flowing through two cylindrical rods of same material. The diameters of the rods are in the ratio $1 : 2$ and their lengths are in the ratio $2 : 1$ . If the temperature difference between their ends is the same, the ratio of rate of flow of heat through them will be