Entropy

:For other senses of the term entropy, see entropy (disambiguation).

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In thermodynamics and statistical mechanics, the thermodynamic entropy (or simply the entropy) S is a measure of the internal disorder present in a system at thermodynamic equilibrium; or, equivalently, the number of possible internal configurations available to the system. The entropy can also be understood as the "quality" of heat flowing between two bodies. The SI unit of entropy is J·K-1 (joules per kelvin), which is the same as the unit of heat capacity.

Related Topics:
Thermodynamics - Statistical mechanics - Thermodynamic equilibrium - Heat - SI - Joule - Kelvin - Heat capacity

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An important and well-known law of physics, known as the second law of thermodynamics, states that the entropy of an isolated system can never decrease. We will explain the meaning of the "second law" in a subsequent section.

Related Topics:
Law of physics - Second law of thermodynamics - Subsequent section

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The concept of entropy was originally introduced in 1865 by Rudolf Clausius, in the context of classical thermodynamics. In 1877, Ludwig Boltzmann formulated an alternative definition of entropy as a measure of disorder, which is now regarded as one of the basic postulates of the theory of statistical mechanics. The closely-related concept of information entropy, used in information theory, was introduced by Claude Shannon in 1948.

Related Topics:
1865 - Rudolf Clausius - 1877 - Ludwig Boltzmann - Statistical mechanics - Information entropy - Information theory - Claude Shannon - 1948

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