 # Boyle's Law

Boyle’s law is an experimental gas law. The relationship between pressure and volume of a gas was 1st noted by Richard Towneley and Henry Power. Then Robert Boyle an anglo-irish natural philosopher, chemist, physicist and inventor confirmed their discovery through experiments and published the results in 1662. This is the reason it is named after Robert Boyle and known as Boyle’s law. The law is also referred as Boyle – Maritte law or Boyle-Maritte’s law as the french physicist Edme Mariotte also discovered the same law independently of Boyle in 1679.

Boyle’s law describes how volume of a gas changes with change in pressure when temperature and mass of the gas are kept constant.

### What is Boyle’s Law?

Boyle’s law states that “the absolute pressure exerted by a given mass of an ideal gas is inversely proportional to the volume it occupies if temperature and amount of gas remain unchanged within a closed system.”

Mathematical expression of Boyle’s law –

P ∝ 1/V--------(1)

Where P is the pressure of the gas and V is the volume of the gas.

It means that for a gas if temperature is maintained constant and number of moles or amount of gas is also kept constant then on increasing the pressure, volume of the gas will decrease. While decreasing the pressure, the volume of the gas will increase.

On removing the proportionality from equation (1) –

PV = k

Where k is the constant.

Thus, Boyle’s law can also be usefully expressed as –

P1V1 = P2V2 = P3V3 = …..= k (Constant)

### Graphical Representation of Boyle’s Law

At constant temperature for a given mass (constant mass) of a gas, if we draw a graph of pressure against volume then we get the following graph –

At constant temperature for a given mass (constant mass) of a gas, if we draw a graph of volume against pressure then we get the same graph as above –

At constant temperature for a given mass (constant mass) of a gas, if we draw a graph of pressure against 1/V then we get the following graph –

At constant temperature for a given mass (constant mass) of a gas, if we draw a graph of volume against 1/P then we get the following graph –

All the graphs above support the statement of Boyle’s Law.

## Applications of Boyle’s Law

Applications of Boyle’s law can be seen in our everyday life. Even the human breathing system is an example of application of Boyle’s law. Few of its real-life applications have been listed below –

• Working of Syringe – The working principle of syringe is based on Boyle’s law. When we pull the plunger of the syringe it increases the volume inside the barrel which causes lower pressure inside it and it results in external fluid to come inside the barrel.

• Human Breathing – As the lungs expands, the volume of the lungs increases so pressure decreases (Boyle’s Law). Now as the pressure is lower inside the body than the outside, so air comes in the lungs from outside. Thus, the inhalation process takes place. While during exhalation, volume of the lungs decreases, and pressure increases so air goes out.

• Bicycle Pump – Working of bicycle pumps is also based on Boyle’s law. It works the same as a syringe.

• Boyle’s law is also used in space by astronauts, scuba drivers etc.

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