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 °C | 273 K |
| 25 °C | 298 K |
| 100 °C | 373 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
- Convert 0 °C to Kelvin.
- Convert 350 K to Celsius.
- What is the Kelvin temperature of a boiling kettle at 100 °C?
- 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)
Revision
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