For heat to flow from one end to the other in a solid,it is necessary to have:

Heat is flowing through a conductor of length $l$ from $x = 0$ to $x = l$. If its thermal resistance per unit length is uniform,which of the following graphs correctly represents the variation of temperature $T$ with distance $x$?

Ice starts forming in a lake with water at $0^{\circ}C$ when the atmospheric temperature is $-10^{\circ}C$. If the time taken for $1 \; cm$ of ice to form is $7$ hours,then the time taken for the thickness of ice to change from $1 \; cm$ to $2 \; cm$ is:

The heat is flowing through a rod of length $50 \ cm$ and area of cross-section $5 \ cm^2$. Its ends are respectively at $25^\circ C$ and $125^\circ C$. The coefficient of thermal conductivity of the material of the rod is $0.092 \ kcal/m \cdot s \cdot ^\circ C$. The temperature gradient in the rod is

When the two ends of a metal rod are maintained at different temperatures and after some time every point of the rod attains a constant temperature,then:

What is heat transfer? Write its modes. In which mode,medium is not required?