The heat flows from a cold body to a hot body with aid of an external source. The statement is given by
Clausius
Heat Flow Principle Explained
Heat transfer is a fundamental concept in thermodynamics, describing how thermal energy moves from one system to another. Naturally, heat flows from a region of higher temperature (a hot body) to a region of lower temperature (a cold body). This spontaneous process is observed in everyday phenomena, such as a hot cup of coffee cooling down or ice melting in a warm room.
Clausius Statement of Thermodynamics
While heat naturally flows from hot to cold, it is possible for heat to flow from a cold body to a hot body. However, this process requires external assistance or an external source of energy. This specific principle is known as the Clausius statement of the Second Law of Thermodynamics. The statement can be formally expressed as:
- It is impossible to construct a device that operates in a cycle and produces no effect other than the transfer of heat from a cooler body to a hotter body.
In simpler terms, to make heat move against its natural gradient (from cold to hot), an external source of work or energy must be supplied. Devices like refrigerators and air conditioners are practical applications of the Clausius statement. They work by extracting heat from a cold space (inside the refrigerator) and releasing it into a warmer space (the room air), but they require an input of work (electrical energy) to operate.
Understanding External Source in Heat Transfer
The "external source" mentioned in the question is crucial. It refers to the work input required to drive the non-spontaneous heat transfer. For instance, in a refrigerator, the compressor performs work to move the refrigerant, enabling it to absorb heat from the cold interior and release it to the warmer surroundings. Without this external work, the transfer of heat from a colder body to a hotter body cannot occur spontaneously.
Why Clausius is the Correct Statement
The question precisely describes the scenario covered by the Clausius statement of the Second Law of Thermodynamics: "The heat flows from a cold body to a hot body with aid of an external source." This distinguishes it from other statements and laws:
- The Clausius statement directly addresses the direction of heat flow when external work is involved.
- It underpins the operation of refrigeration cycles and heat pumps, where work input facilitates heat transfer against a temperature gradient.
Other Scientists and Their Contributions
It is important to differentiate the contributions of other scientists mentioned in the options:
| Scientist | Key Contribution (Related to Thermodynamics) |
|---|---|
| Kelvin | William Thomson (Lord Kelvin) contributed significantly to thermodynamics, including the absolute temperature scale (Kelvin scale) and the Kelvin-Planck statement of the Second Law of Thermodynamics. This statement is about the impossibility of creating a perpetual motion machine of the second kind, which converts heat entirely into work from a single heat reservoir. |
| Joule | James Prescott Joule established the mechanical equivalent of heat, demonstrating that heat and mechanical work are interconvertible forms of energy. His work laid the foundation for the First Law of Thermodynamics (conservation of energy). |
| Clausius | Rudolf Clausius made significant contributions to the foundation of thermodynamics, notably formulating the Second Law of Thermodynamics and introducing the concept of entropy. His statement directly addresses the condition under which heat flows from a cold body to a hot body, requiring an external source. |
| Gay-Lussac | Joseph Louis Gay-Lussac is primarily known for Gay-Lussac's Law, which describes the relationship between pressure and temperature of gases at constant volume. This is part of the ideal gas laws and is not directly related to the Second Law of Thermodynamics' statements on the direction of heat flow with external aid. |
Therefore, based on the description that heat flows from a cold body to a hot body with aid of an external source, the statement accurately reflects the principle put forth by Clausius.
Important Questions from Statements of Second Law of Thermodynamics
Which law of thermodynamics assigns a quality to different form of energy, and also indicates the direction of any spontaneous process?
- The direction of the natural process is defined by ______.
Identify the correct option with respect to the second law of thermodynamics.
I) It gives the concept of temperature
II) It gives the concept of internal energy
III) it gives the concept of entropy
Which of following is true with respect to PMM2?
The statement ‘It is impossible to construct a device that operates in a cycle and produces no effect other than the transfer of heat from a lower-temperature body to a higher-temperature body’ is known as:
