The Kelvin Scale & Absolute Zero (AQA A Level Physics)

The Kelvin Scale & Absolute Zero

• On the thermodynamic (Kelvin) temperature scale, absolute zero is defined as:

  The lowest temperature possible. Equal to 0 K or -273.15 °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

• Absolute zero is defined s as:

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

• This means for a system at 0 K, it is not possible to remove any more energy from it

• Even in space, the temperature is roughly 2.7 K, just above absolute zero

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 − 273.15

T / K = θ / ^°C + 273.15

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

• This is why when using the specific heat capacity equation

Q = mcΔθ

• Δθ does not require the temperature to be in either unit

  • This is because the difference in temperature between two values whether in Kelvin or Celsius will be exactly the same