NCERT Class 11 Physics Solutions: Chapter 12 – Thermodynamics-Part 1

Get unlimited access to the best preparation resource for NSO : fully solved questions with step-by-step explanation- practice your way to success.

Question 12.1:

A geyser heats water flowing at the rate of per minute from . If the geyser operates on a gas burner, what is the rate of consumption of the fuel if its heat of combustion is


Water is flowing at a rate of .

Water is flowing at a rate of

Initial temperature,

Final temperature,

Heat of combustion

Specific heat of water,

Mass of flowing water,

Total heat used,

Question 12.2:

What amount of heat must be supplied to of nitrogen (at room temperature) to raise its temperature by at constant pressure?

(Molecular mass of


Mass of nitrogen,

Rise in temperature,

Molecular mass of

Universal gas constant,

Number of moles,

Molar specific heat at constant pressure for nitrogen

The total amount of heat to be supplied is given by the relation:

Therefore, the amount of heat to be supplied is

Question 12.3:

Explain why

a) Two bodies at different temperatures if brought in thermal contact do not necessarily settle to the mean temperature

b) The coolant in a chemical or a nuclear plant (i.e., the liquid used to prevent the different parts of a plant from getting too hot) should have high specific heat.

c) Air pressure in a car tyre increases during driving. d) The climate of a harbor town is more temperate than that of a town in a desert at the same latitude.



When two bodies at different temperatures are brought in thermal contact, heat flows from the body at the higher temperature to the body at the lower temperature till equilibrium is achieved, i.e., the temperatures of both the bodies become equal. The equilibrium temperature is equal to the mean temperature only when the thermal capacities of both the bodies are equal.


The coolant in a chemical or nuclear plant should have a high specific heat. This is because higher the specific heat of the coolant, higher is its heat-absorbing capacity and vice versa. Hence, a liquid having a high specific heat is the best coolant to be used in a nuclear or chemical plant. This would prevent different parts of the plant from getting too hot.


When a car is in motion, the air temperature inside the car increases because of the motion of the air molecules. According to Charles’ law, temperature is directly proportional to pressure. Hence, if the temperature inside a tyre increases, then the air pressure in it will also increase.


A harbor town has a more temperate climate (i.e., without the extremes of heat or cold) than a town located in a desert at the same latitude. This is because the relative humidity in a harbor town is more than it is in a desert town.