Absolute Zero (Edexcel GCSE Physics)

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Absolute Zero

  • The amount of pressure that a gas exerts on its container is dependent on the temperature of the gas
    • This is because particles move with more energy as their temperature increases

  • As the temperature of the gas decreases, the pressure on the container also decreases
  • In 1848, Mathematician and Physicist, Lord Kelvin, recognised that there must be a temperature at which the particles in a gas exert no pressure
    • At this temperature they must no longer be moving, and hence not colliding with their container

  • This temperature is called absolute zero and is equal to -273 °C

Pressure Law, downloadable AS & A Level Physics revision notes

At absolute zero, or -273 °C, particles will have no net movement. It is therefore not possible to have a lower temperature

  • Absolute zero is defined as:

The temperature at which the molecules in a substance have zero kinetic energy 

  • This means for a system at absolute zero, it is not possible to remove any more energy from it
  • Even in space, the temperature is roughly 2.7 °C above absolute zero

The Kelvin Temperature Scale

  • The Kelvin temperature scale begins at absolute zero
    • 0 K is equal to -273 °C 
    • An increase of 1 K is the same change as an increase of 1 °C

  • It is not possible to have a temperature lower than 0 K
  • This means a temperature in Kelvin will never be a negative value

Using the Kelvin Scale

  • To convert between temperatures θ in the Celsius scale, and T in the Kelvin scale, use the following conversion:

θ / °C = T / K − 273

T / K = θ / °C + 273

K and Celsius conversion chart, downloadable AS & A Level Physics revision notes

Conversion chart relating the temperature on the Kelvin and Celsius scales

  • The divisions on both scales are equal. This means:

A change in a temperature of 1 K is equal to a change in temperature of 1 °C

Worked example

The temperature in a room is 300 K.What is this temperature in Celsius?

Step 1: Kelvin to Celsius equation

θ / °C = T / K − 273

Step 2: Substitute in value of 300 K

300 K − 273 = 27 °C

Examiner Tip

If you forget in the exam whether it’s +273 or −273, just remember that 0 °C = 273 K. This way, when you know that you need to +273 to a temperature in degrees to get a temperature in Kelvin. For example:  0 °C + 273 = 273 K.

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Ashika

Author: Ashika

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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.