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Pressure and volume of a gas (Boyle's Law)
Imagine a gas is trapped in a cylinder by a piston.
If the piston is pushed in, the gas particles will have less room to move as the volume the gas occupies has been decreased.
Process of equilibrium
Because there has been a decrease in volume the particles will collide more frequently with the walls of the container. Each time they collide with the walls, they exert a force on them. More collisions mean more force, so the pressure will increase.
When the volume decreases the pressure increases. This shows that the pressure of a gas is inversely proportional to its volume.
From this we can derive the equation:
Where:
is the starting pressure 
is the starting volume 
is the finishing pressure
is the finishing volume
- Question
A sealed syringe contains 10 10-6 m3 of air at 1 × 105 Pa. The plunger is pushed until the volume of trapped air is 4 10-6 m3. If there is no change in temperature what is the new pressure of the gas?
- Answer
= 1 × 105 Pa
= 10 × 10-6 m3
= 4 × 10-6 m3
Therefore,
= 2.5 × 105 PaThe new pressure in the syringe is 2.5 × 105 Pa
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SQA - Physics
Scottish Qualifications Authority Physics resources, including Past Papers and Arrangements Documents.
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