PMM2 Violation Explained: Kelvin-Planck Statement

The question asks which statement is true regarding a Perpetual Motion Machine of the Second Kind (PMM2). Let's analyze the options in the context of thermodynamics.

Understanding PMM2

A Perpetual Motion Machine of the Second Kind (PMM2) is a hypothetical device that operates in a cycle and aims to convert heat energy, sourced from a single thermal reservoir, completely into mechanical work, without any other effects.

The Kelvin-Planck Statement

The Kelvin-Planck statement is a fundamental principle of the Second Law of Thermodynamics. It states:

"It is impossible for any device that operates on a cycle to receive heat from a single reservoir and produce a net amount of work."

In simpler terms, you cannot build a machine that, by itself, cools down a single heat source (like a reservoir) and produces work from that heat alone. Some heat must always be rejected to a colder reservoir.

Analyzing the Options

• Option 1: It violates the Kelvin-Planck statement.

  This is correct. A PMM2, by definition, aims to do exactly what the Kelvin-Planck statement declares impossible: converting heat from a single source entirely into work in a cycle.

• Option 2: It violates Joule's effect.

  Joule's effect relates to the heat produced when current flows through a resistance. This is unrelated to the core principle violated by PMM2.

• Option 3: It violates the concept of temperature.

  PMM2 operates based on temperature differences (heat transfer), but it doesn't violate the fundamental concept or definition of temperature itself.

• Option 4: It violates the statement that the total energy of the universe is constant.

  The statement that total energy is constant relates to the First Law of Thermodynamics (Conservation of Energy). A PMM2 might not necessarily violate energy conservation (it could potentially take in heat energy and output equal work energy), but it fundamentally violates the efficiency limitations and directional constraints imposed by the Second Law of Thermodynamics, as articulated by the Kelvin-Planck statement.

Conclusion

Therefore, the defining characteristic of a Perpetual Motion Machine of the Second Kind (PMM2) is its direct violation of the Kelvin-Planck statement, a core tenet of the Second Law of Thermodynamics.