Exercise-1

Three rods of the same dimensions have thermal conductivities $3\mathrm{k},2\mathrm{k}$ and $k$. They are arranged as shown with their ends at $100°\mathrm{C}, 50°\mathrm{C}$ and $0°\mathrm{C}$. The temperature of their junction is:

A cup of tea cools from $80°\mathrm{C} \mathrm{to} 60°\mathrm{C}$ in $\mathrm{one} \mathrm{minute}$. The ambient temperature is $30°\mathrm{C}$. In cooling from $60°\mathrm{C}$ to $50°\mathrm{C}$. It will take:

There is a small hole in a container. At what temperature should it be maintained in order that it emits $\mathrm{one} \mathrm{calorie}$ of energy  $\mathrm{per} \mathrm{second} \mathrm{per} {\mathrm{meter}}^2$:

Two different rods $A$ and $B$ are kept as shown in figure. The variation of temperature of different cross sections with distance is plotted in a graph shown in figure. The ratio of thermal conductivities of $A$ and $B$ is:

The area of cross-section of rod is given by $A=A_0\left(1+\alpha x\right)$ where $A_0 \& \alpha$ are constant and $x$ is the distance from one end. If the thermal conductivity of the material is $K$, what is the thermal resistance of the rod if its length is $l_0$?

Which of the following graph shows the correct variation in intensity of heat radiations by black body and frequency at a fixed temperature:

A red star and a green star radiate energy at the same rate which star is bigger.

Water is used to cool the radiators of engines in cars because