Question

“Heat cannot flow by itself from a body at lower temperature to a body at higher temperature” and can be done by the supply of external work is

• A. Kelvin Planck statement of second law of thermodynamics
• B. First law of thermodynamics
• C. Zeroth law of thermodynamics
• D. Clausius statement of second law of thermodynamics

Hint:

Distinguish between the two main statements of the Second Law of Thermodynamics: - \textbf{Clausius Statement}: Focuses on the natural direction of heat flow (hot to cold) and the necessity of external work to reverse it (refrigerators/heat pumps). - \textbf{Kelvin-Planck Statement}: Focuses on the impossibility of a perfectly efficient heat engine (i.e., extracting heat from a single reservoir and producing net work without rejecting heat).

Answer 1

The Correct Option is D

Step 1: Understand the fundamental laws of thermodynamics.
Zeroth Law of Thermodynamics: Deals with thermal equilibrium. It states that if two systems are each in thermal equilibrium with a third system, then they are in thermal equilibrium with each other. This law defines temperature.
First Law of Thermodynamics: Deals with the conservation of energy. It states that energy cannot be created or destroyed, only transferred or changed from one form to another. The mathematical expression is typically \( \Delta U = Q - W \).
Second Law of Thermodynamics: Deals with the direction of heat flow and the quality of energy (entropy). It has several equivalent statements.
Step 2: Analyze the given statement.
The statement is: "Heat cannot flow by itself from a body at lower temperature to a body at higher temperature" and "can be done by the supply of external work".
This statement describes the natural direction of heat flow (from hot to cold) and the condition under which heat can flow from cold to hot (i.e., with external work input, as in a refrigerator or heat pump).
Step 3: Relate the statement to the different laws/statements of thermodynamics.
Kelvin-Planck statement of the Second Law: States that it is impossible to construct a device operating in a cycle that produces no effect other than the transfer of heat from a single thermal reservoir and the production of an equivalent amount of work. This is related to the impossibility of a perpetual motion machine of the second kind and focuses on the work-heat conversion efficiency.
First Law of Thermodynamics: Focuses on energy conservation, not the direction of processes.
Zeroth Law of Thermodynamics: Focuses on temperature and thermal equilibrium.
Clausius statement of the Second Law: States that it is impossible to construct a device operating in a cycle that produces no effect other than the transfer of heat from a colder body to a hotter body. This directly addresses the natural direction of heat flow and the requirement of external work for reverse heat transfer. The part "can be done by the supply of external work" further clarifies that this is precisely what a refrigerator or heat pump does, and they require external work. Therefore, the given statement is the direct definition of the Clausius statement of the second law of thermodynamics. The final answer is \( \boxed{\text{4}} \).