Boyle's Law (Edexcel GCSE Physics)

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Calculating Change in Pressure & Volume

  • For a fixed mass of a gas held at a constant temperature:

pV = constant

  • Where:
    • p = pressure in pascals (Pa)
    • V = volume in metres cubed (m3)

  • This means that the pressure and volume are inversely proportional to each other
    • When the volume decreases (compression), the pressure increases
    • When the volume increases (expansion), the pressure decreases

  • This is because when the volume decreases, the same number of particles collide with the walls of a container but more frequently as there is less space
    • However, the particles still collide with the same amount of force meaning greater force per unit area (pressure)

  • The key assumption is that the temperature and the mass (and number) of the particles remains the same

Gas Laws Molecular Model (1), downloadable AS & A Level Physics revision notes

Increasing the volume of a gas decreases its pressure

  • This equation can also be rewritten for comparing the pressure and volume before and after a change in a gas:

P1V1 = P2V2

  • Where:
    • P1 = initial pressure in pascals (Pa)
    • V1 = initial volume in metres cubed (m3)
    • P2 = final pressure in pascals (Pa)
    • V2 = final volume in metres cubed (m3)

  • This equation is sometimes referred to as Boyle's Law

Pressure-vs-Volume, IGCSE & GCSE Physics revision notes

Initial pressure and volume, P1 and V1, and final pressure and volume, P2 and V2

Worked example

A gas occupies a volume of 0.70 m³ at a pressure of 200 Pa. Calculate the pressure exerted by the gas if it is compressed to a volume of 0.15 m³.Assume that the temperature and mass of the gas stay the same.

Boyle's Law Worked Example

Examiner Tip

Always check whether your final answer makes sense. If the gas has been compressed, the final pressure is expected to be more than the initial pressure (like in the worked example).If this is not the case, double-check the rearranging of any formulae and the values put into your calculator.One pascal is a very small amount of pressure, and you will typically meet pressures in the order of kilo-pascals. The pressure on you at the moment because of the air around you is equal to 100 kPa, so use this as reference when considering if your answer makes sense.

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Ashika

Author: Ashika

Expertise: Physics Project Lead

Ashika graduated with a first-class Physics degree from Manchester University and, having worked as a software engineer, focused on Physics education, creating engaging content to help students across all levels. Now an experienced GCSE and A Level Physics and Maths tutor, Ashika helps to grow and improve our Physics resources.