convert temperatures between kelvin and degrees Celsius and recall that T / K = θ / °C + 273.

Temperature Scales: Kelvin & Celsius

Temperature tells us how hot or cold something is. In physics we usually use two main scales: Celsius (°C) and Kelvin (K). The Kelvin scale is the SI unit for temperature, while Celsius is handy for everyday life. The two are linked by a simple formula:

\$T{\text{K}} = \theta{\text{°C}} + 273\$

Think of it like a number line that starts at 0°C (the freezing point of water) and goes up to 100°C (the boiling point). Kelvin just shifts that line so that 0 K is absolute zero – the coldest possible temperature. That shift is exactly 273 K.

Quick Conversion Rules

  • To go from Celsius to Kelvin: add 273.

  • To go from Kelvin to Celsius: subtract 273.

Example 1: 25 °C → 25 + 273 = 298 K.

Example 2: 310 K → 310 − 273 = 37 °C.

Visualising the Shift

Celsius (°C)Kelvin (K)
0 °C273 K
25 °C298 K
100 °C373 K

Analogy: The Temperature “Scale‑Shift”

Imagine you have a ruler that starts at 0 °C. If you want to measure the same distance but in Kelvin, you simply move the ruler 273 units to the right. That’s why the formula is just a shift – no stretching or squishing, just a translation.

Exam Tip Box

Tip: When you see a question asking for a temperature in Kelvin, remember the quick rule: add 273. If the answer seems too high or too low, double‑check that you didn’t accidentally add 273 to a Kelvin value instead of subtracting it.

Practice Problems

  1. Convert 0 °C to Kelvin.

  2. Convert 350 K to Celsius.

  3. What is the Kelvin temperature of a boiling kettle at 100 °C?

  4. If a thermometer reads 200 K, what is the temperature in °C?

🔥 Challenge: The freezing point of water is 0 °C. What is the temperature of absolute zero in Celsius? (Hint: 0 K = -273 °C)