# Charles's law

Charles's law (sometimes called the Law of Charles and Gay-Lussac) is one of the gas laws; it relates the volume and temperature of an ideal gas held at a constant pressure. The law was first published by Joseph Louis Gay-Lussac in 1802, but he referenced unpublished work by Jacques Charles from around 1787. This reference has led to the law being attributed to Charles.

The law, expressed in symbols, is:

[itex]\frac{T}{V} = k[itex]

where

V is the volume (measured in cubic metres in SI)

T is the temperature (measured in kelvins in SI)

k is a constant.

To maintain the constant during heating of a gas at fixed pressure, the volume must increase. Conversely, cooling the gas decreases the volume. The exact value of the constant need not be known to make use of the law in comparison between two volumes of gas at equal pressure:

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