Boyle's law

File:Boyle.jpg

Diagram of Boyle's mercurial gauge, "to discover the degrees both of rarified and condensed air." Boyle's diagram from a later experiment used a Torricellian barometer in which the mercury reservoir was contained within a glass vessel which was evacuated by an air pump.

Boyle's law (sometimes called the Boyle Mariotte law) is one of the gas laws. Boyle's Law is named after the Irish natural philosopher Robert Boyle (1627-1691) who discovered it in 1662. Edme Mariotte (1620-1684) was a French physicist who discovered the same law independently of Boyle in 1676, so this law is often known as Mariotte's or Mariotte Boyle law.

Boyle's Law states that the product of the volume and pressure of a fixed quantity of an ideal gas is constant, given constant temperature. Expressed mathematically, the formula for Boyle's law is:

$\qquad \qquad PV=k$

where:

• V is volume of the gas.
• P is the pressure of the gas.
• k is a constant.

To maintain the constant during an increase in pressure of a gas, at fixed temperature, requires that the volume decrease. Conversely, reducing the pressure of the gas increases the volume.

The exact value of the constant k need not be known when measuring the "before" (subscript 1)and "after" (subscript 2) volumes and pressures of a fixed amount of gas when the "before" and "after" temperatures are the same. (If the "after" volume of gas is different from the "before" volume, the "after" volume and the "after" pressure of the fixed amount of gas can not be measured until it has been heated or cooled to the "before" temperature.) The "before" and "after" states are related by the following equation:

$\qquad P_{1}V_{1}=P_{2}V_{2}$

Boyle's law, Charles's Law, and Gay-Lussac's Law form the combined gas law. The three gas laws in combination with Avogadro's Law can be generalized by the ideal gas law.

See also

• Scientific laws named after people

External links

• Boyle's Law at the Scuba Guide. Understanding Boyle's law is an important part of scuba certification; see Boyle's law explained in a scuba context.