Temperature Scales (DP IB Physics: SL): Revision Note
Temperature Scales
On the thermodynamic (Kelvin) temperature scale, absolute zero refers to the lowest possible temperature
This is equal to 0 K or −273 °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 as:
The temperature at which the molecules in a substance have zero kinetic energy
This means that 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
How to use 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
Conversion chart between temperature scales in Kelvin and Celsius
The divisions on both scales are equal, which means
A change in a temperature of 1 K is equal to a change in temperature of 1 °C
Worked Example
In many ideal gas problems, room temperature is considered to be 300 K.
What is this temperature in degrees Celsius?
Answer:
Step 1: Recall the Kelvin to Celsius conversion
θ / °C = T / K − 273
Step 2: Substitute in the value of 300 K
300 K − 273 = 27 °C
Examiner Tips and Tricks
If you forget in the exam whether it’s + or −273, check the data booklet!
Temperature (K) = temperature (°C) + 273
This helpful reminder is there under 'unit conversions'
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