Why do some cooking vessels have a copper coating at the bottom?

If the radius and length of a copper rod are both doubled,the rate of flow of heat along the rod increases ....... times.

Two metal rods $P$ and $Q$ have the same length and the same temperature difference between their ends. Their thermal conductivities are $K_1$ and $K_2$,and their cross-sectional areas are $A_1$ and $A_2$ respectively. If the rate of flow of heat through rod $Q$ is three times that in rod $P$,then:

$A$ cylindrical steel rod of length $0.10 \,m$ and thermal conductivity $50 \,Wm^{-1}K^{-1}$ is welded end to end to a copper rod of thermal conductivity $400 \,Wm^{-1}K^{-1}$ and of the same area of cross-section but $0.20 \,m$ long. The free end of the steel rod is maintained at $100^{\circ}C$ and that of the copper rod at $0^{\circ}C$. Assuming that the rods are perfectly insulated from the surroundings,the temperature at the junction of the two rods is ................... $^{\circ}C$.

For cooking the food,which of the following type of utensil is most suitable?

The thermal conductivities of copper,mercury,and glass are $K_c$,$K_m$,and $K_g$ respectively,such that $K_c > K_m > K_g$. If the same amount of heat flows per unit time through a unit cross-sectional area for each,what is the relationship between their temperature gradients $(X_c, X_m, X_g)$?