A cup of tea cools from $80\,^oC$ to $60\,^oC$ in one minute. The ambient temperature is $30\,^oC$. In cooling from $60\,^oC$ to $50\,^oC$. It will take ……. $\sec$

Two rods $A$ and $B$ of different materials but same cross section are joined as in figure. The free end of $A$ is maintained at $100^o C$ and the free end of $B$ is maintained at $0^o C$. If $l_2 = 2l_1, K_1 = 2K_2$ and rods are thermally insulated from sides to prevent heat losses then the temperature $\theta$ of the junction of the two rods is …….. $^oC$

A cylindrical metallic rod in thermal contact with two reservoirs of heat at its two ends conducts an amount of heat $Q$ in time $t$. The metallic rod is melted and the material is formed into a rod of half the radius of the original rod. What is the amount of heat conducted by the new rod, when placed in thermal contact with same two reservoirs in time $t$

Three rods of same dimensions have thermal conductivities $3K,\,2K$ and $K$. They are arranged as shown with their ends at $100\,^oC$, $50\,^oC$ and $0\,^oC$. Temperature of junction is

Which of the following material is most suitable for cooking utensil?