Class 11 Physics Important Chapter 12 Thermodynamics

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Class 11 Physics Important Chapter 12 Thermodynamics

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Thermodynamics

Chapter: 12

IMPORTANT QUESTION AND ANSWER

Answer the Following Questions:

1. What is the Zeroth Law of Thermodynamics?

Ans: The Zeroth Law of Thermodynamics states that if two systems are each in thermal equilibrium with a third system, then they are in thermal equilibrium with each other.

2. What is specific heat capacity?

Ans: Specific heat capacity is the amount of heat required to raise the temperature of a unit mass of a substance by one degree Celsius (or one Kelvin).

3. What does the First Law of Thermodynamics state?

Ans: The First Law of Thermodynamics states that the change in internal energy of a system is equal to the heat supplied to the system minus the work done by the system, i.e., ΔQ = ΔU + ΔW.

4. What is an isothermal process?

Ans: An isothermal process is a thermodynamic process in which the temperature of the system remains constant. In an isothermal expansion or compression, the heat added or removed is completely converted into work.

5. State and explain the second law of thermodynamics.

Ans: The Second Law of Thermodynamics states that the efficiency of a heat engine can never be 100%, and no process is possible whose sole result is the transfer of heat from a colder body to a hotter body.

6. What is the principle of conservation of energy in thermodynamics?

Ans: The principle of conservation of energy states that energy can neither be created nor destroyed, but can only be converted from one form to another. In thermodynamics, this is represented by the First Law, which states that the change in internal energy of a system is equal to the heat supplied minus the work done by the system:

ΔQ = ΔU + ΔW

7. What is the significance of the Carnot cycle?

Ans: The Carnot cycle is a theoretical thermodynamic cycle that provides the maximum possible efficiency for a heat engine working between two temperatures. It consists of two isothermal processes and two adiabatic processes. 

The efficiency of the Carnot engine is given by the formula:

8. What is the work done by an ideal gas in an isothermal process?

Ans: In an isothermal process, the temperature of the gas remains constant, and thus its internal energy does not change. The work done by the gas during an isothermal expansion or compression is given by the equation:

where V₁ and V₂  are the initial and final volumes, n is the number of moles, and T is the constant temperature.

9. What is an adiabatic process, and how is it different from an isothermal process?

Ans: An adiabatic process is one in which no heat is exchanged with the surroundings, i.e., ΔQ = 0. In contrast, an isothermal process occurs at a constant temperature, where heat is transferred to or from the system to maintain constant temperature. In an adiabatic process, the change in internal energy results purely from the work done by or on the system, whereas in an isothermal process, the work done is balanced by the heat added or removed.

10. Explain the concept of quasi-static processes in thermodynamics.

Ans: A quasi-static process is an idealized thermodynamic process that happens infinitely slowly, ensuring the system remains in thermal and mechanical equilibrium with its surroundings at every stage. This process is reversible and involves infinitesimal changes in pressure, volume, or temperature.

11. What is an isobaric process, and how does it differ from an isochoric process?

Ans: An isobaric process is a thermodynamic process in which the pressure of the system remains constant while its volume and temperature change. In contrast, an isochoric process occurs at constant volume, where no work is done on or by the system, and heat added to the system increases its internal energy and temperature.

12. What is the Carnot cycle?

Ans: The Carnot cycle is a theoretical thermodynamic cycle that provides the maximum possible efficiency for a heat engine. It consists of two isothermal processes (heat absorption and heat rejection) and two adiabatic processes (expansion and compression). The efficiency of a Carnot engine depends only on the temperatures of the hot and cold reservoirs and is given by:

where T_1​ and T₂ are the temperatures of the hot and cold reservoirs, respectively.

13. Differentiate between isothermal and adiabatic changes.

Ans: 

Isothermal Change	Adiabatic Change
(i) The temperature of the system remains constant during the process.	(i) The temperature of the system changes during the process.
(ii)  Heat is exchanged with the surroundings to maintain constant temperature.	(ii) No heat is exchanged with the surroundings; the system is thermally insulated.
(iii) The work done by the system is balanced by heat absorbed or released.	(iii) Work done on or by the system results in a change in internal energy, which causes a change in temperature.
(iv) For an ideal gas, the internal energy remains constant as there is no temperature change.	(iv) The internal energy changes due to work done on or by the system, which causes temperature changes.
(v) Expansion or compression of an ideal gas in a piston in contact with a heat reservoir.	(v) Free expansion of gas, or expansion/compression without heat exchange (e.g., a gas in an insulated cylinder).

14. No real engine can have an efficiency greater than that of a Carnot engine working between the same two temperatures. Why?

Ans. A carnot engine is an ideal heat engine due to following reasons:

(i) There is absolutely no friction between the walls of the cylinder and piston.

(ii) The working substance is an ideal gas.

In a real engine, these conditions can not be fulfilled and hence no heat engine working between the same two temperatures can have efficiency greater than that of carnot engine.

15. Explain the significance of the coefficient of performance (COP) of a refrigerator.

Ans: The coefficient of performance (COP) of a refrigerator is a measure of its efficiency, defined as the ratio of the heat removed from the cold reservoir (Qc) to the work input required to transfer the heat (W):

A higher COP indicates a more efficient refrigerator, requiring less work to transfer a given amount of heat.