Rate of flow of heat through a cylindrical rod is $H_1$. The temperatures at the ends of the rod are $T_1$ and $T_2$. If all the dimensions of the rod become double and the temperature difference remains the same,the rate of flow of heat becomes $H_2$. Then:

The end $A$ of a rod $AB$ of length $1\,m$ is maintained at $80\,^{\circ}C$ and the end $B$ at $0\,^{\circ}C$. The temperature at a distance of $60\,cm$ from the end $A$ is......... $^{\circ}C$

The temperature difference between two sides of a metal plate,$3 \ cm$ thick,is $15^{\circ} C$. Heat is transmitted through the plate at the rate of $900 \ kcal$ per minute per $m^2$ at steady state. The thermal conductivity of the metal is:

Mud houses are cooler in summer and warmer in winter because

$A$ 'thermacole' icebox is a cheap and an efficient method for storing small quantities of cooked food in summer in particular. $A$ cubical icebox of side $30 \,cm$ has a thickness of $5.0 \,cm$. If $4.0 \,kg$ of ice is put in the box,estimate the amount of ice (in $kg$) remaining after $6 \,h$. The outside temperature is $45 \,^{\circ}C$,and the coefficient of thermal conductivity of thermacole is $0.01 \,J \,s^{-1} \,m^{-1} \,K^{-1}$. Heat of fusion of water $= 335 \times 10^{3} \,J \,kg^{-1}$.

Copper and iron rods of identical dimensions are coated with wax. The ratio of thermal conductivity of copper to iron is $10:9$. If one end of each rod is placed in hot water,the wax melts. Find the ratio of the lengths of the rods for which the wax melts at the same rate.