Boyle's Law

The volume of a fixed mass of gas is inversely proportional to its pressure at constant temperature.


p ∝ 1 / v
p = k 1 /v
pv = k

Please move the slider and experiment with it.

P ∝ 1 / V

If the pressure and volume of a fixed mass of gas take the values of p1 v1and p2 v2 respectively,

p1 v1 = p2 v2


The pressure of a fixed mass of air is 20 Pa and volume is 8 cm3. Its pressure is doubled while keeping the temperature constant. Find the volume.
p1 = 20, v1 = 8, p2 = 40
According to Boyle's law,
p1v1 = p2v2
20 x 8 = v2 x 40
v2 = 4cm3

The following animation shows how the lungs function, following Boyle's Law.

Please answer the following questions.

  1. An air column is trapped inside a capillary tube by a drop of mercury. The tube is placed horizontally and the position of the mercury drop is noted. Then the tube is raised vertically with the open end being at the top. What will happen to the mercury column? - go up or down.
  2. When a coke bottle is opened, air bubbles go up from the bottom. Explain this.
  3. A balloon filled with air is brought down in a lake; the deeper it goes, the more it tends to go up. Explain.
  4. A 1.5 litre can is filled with nitrogen at a pressure of 8 atmospheres. What size can would be required to hold the same gas at a pressure of 4.0 atmospheres?.
  5. Can you apply Boyle's law when a car tire is being filled up?. Explain you answer.
  6. Two identical containers of volume 6cm3 contain the same gas at pressure 20 Pa and 12 Pa. They are linked by a valve-tube. When the valve is opened, find the resultant pressure of the system.