Charles's law

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Charles' law (sometimes called the Law of Charles and Gay-Lussac) is one of the gas laws. It states that at constant pressure, the volume of a given mass of a ideal gas increases or decreases by the same factor as its temperature (in kelvins) increases or decreases.

The law was first published by Joseph Louis Gay-Lussac in 1802, but he referenced unpublished work by Jacques Charles from around 1787.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 relationship had been anticipated by the work of Guillaume Amontons in 1702.

The formula for the law is:

$\frac{V}{T} = k$

-where:

V is the volume.
T is the temperature (measured in kelvins).
k is a constant.

To maintain the constant, k, 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:

$\frac{V_1}{T_1} = \frac{V_2}{T_2} \qquad \mathrm{or} \qquad \frac {V_2}{V_1} = \frac{T_2}{T_1} \qquad \mathrm{or} \qquad V_1T_2 = V_2T_1$ .