kelvin planck statement

What is the Kelvin Planck Statement?

The Kelvin Planck statement of the second law of thermodynamics states that it is impossible for any heat engine to have a thermal efficiency of 100%, meaning that it is impossible to convert all of the heat absorbed by the engine into work. In other words, there will always be some heat that is not converted into work and is instead exhausted as waste heat.

kelvin planck statement of second law of thermodynamics

The Kelvin-Planck statement of the second law of thermodynamics states that it is impossible for any heat engine to have a thermal efficiency of 100%, or for any process to have a thermal efficiency of 100%. This means that in any heat engine or thermodynamic process, some energy will inevitably be wasted as heat and cannot be converted into useful work.

Kelvin Planck Statement Example

An example of the Kelvin-Planck statement of the second law of thermodynamics in action is a car engine. The energy from the fuel is used to heat up the engine, which then causes the pistons to move, turning the wheels of the car and producing useful work. However, not all of the energy from the fuel is converted into useful work – some is lost as heat through the exhaust and through friction in the engine. The thermal efficiency of a car engine is typically around 25-30%, meaning that only a quarter to a third of the energy from the fuel is converted into useful work, with the rest being wasted as heat.

Working of Heat Engine

A heat engine is a device that converts heat energy into mechanical energy. It operates on the principle of the Kelvin-Planck statement of the second law of thermodynamics, which states that it is impossible for any heat engine to have a thermal efficiency of 100%.

The basic working of a heat engine can be explained using the Carnot cycle. The Carnot cycle is a theoretical heat engine cycle that consists of four stages:

  1. Isothermal expansion: In this stage, heat is added to the working fluid (usually a gas) at a constant temperature, causing the gas to expand and do work on the surroundings.
  2. Adiabatic expansion: In this stage, the working fluid expands without exchanging heat with the surroundings, causing the temperature of the fluid to decrease.
  3. Isothermal compression: In this stage, heat is removed from the working fluid at a constant temperature, causing the gas to compress and do work on the surroundings.
  4. Adiabatic compression: In this stage, the working fluid is compressed without exchanging heat with the surroundings, causing the temperature of the fluid to increase.

The Carnot cycle is the most efficient heat engine cycle possible, and its thermal efficiency is dependent on the temperature difference between the heat source and the heat sink. The higher the temperature difference, the more efficient the cycle. However, as per the Kelvin-Planck statement of the second law of thermodynamics, the thermal efficiency of a Carnot cycle is always less than 100%.

In reality, the heat engine’s efficiency is lower due to losses such as internal friction, leakage, and other real-world factors.

who is kelvin planck

Lord Kelvin (William Thomson) and Max Planck were both prominent scientists in the field of thermodynamics and physics.

Lord Kelvin (William Thomson) was a Scottish mathematician, physicist, and engineer who lived in the 19th century. He made significant contributions to the fields of thermodynamics, electromagnetism, and the study of the Earth’s magnetic field. He is best known for his work on the second law of thermodynamics, in which he proposed the concept of the “absolute zero” of temperature and formulated the Kelvin scale of temperature. He also proposed the concept of the “available energy” and formulated the Kelvin-Planck statement of the second law of thermodynamics.

Max Planck was a German physicist who lived in the late 19th and early 20th century. He is best known for his work on quantum theory, which led to the development of quantum mechanics. He also made contributions to the field of thermodynamics and statistical mechanics. He formulated the Planck distribution law, which describes the distribution of energy in a system of non-interacting particles in thermal equilibrium.

Both scientists formulated similar versions of the second law of thermodynamics independently, therefore it is often referred as Kelvin-Planck statement of the second law of thermodynamics.

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