OCR · A-Level · Physics
Course version: H556 · Version from Sept 2015
Temperature: (d) T(K) ≈ θ(°C) + 273
The relationship T(K) ≈ θ(°C) + 273 allows you to convert a temperature from degrees Celsius to kelvin.
Checked against the OCR H556 specification (opens in a new tab) on .
- Point 4 of 4
Study notes
From the checked teaching notes for this specification point.
The idea
The relationship T(K) ≈ θ(°C) + 273 allows you to convert a temperature from degrees Celsius to kelvin. Here, T is the thermodynamic temperature in kelvin and θ is the Celsius temperature. The approximation is used because the exact offset is 273.15, but for many calculations 273 is sufficient. For example, 20 °C is approximately 293 K. To convert from kelvin to Celsius, rearrange the equation: θ(°C) ≈ T(K) − 273. Always check the direction of conversion and whether the question expects the approximate or exact value.
What earns the marks
- The equation T(K) ≈ θ(°C) + 273 converts a Celsius temperature to kelvin.
- T represents the thermodynamic temperature in kelvin and θ represents the Celsius temperature.
- The approximation uses 273 instead of the exact 273.15.
- To convert from kelvin to Celsius, rearrange to θ(°C) ≈ T(K) − 273.
- A temperature change of 1 °C equals a temperature change of 1 K, so the equation also applies to temperature differences.
Common mistakes and how to put them right
Misunderstanding: to convert from kelvin to Celsius, add 273.
Put it right: Subtract 273, so θ(°C) ≈ T(K) − 273.
Misunderstanding: the equation gives an exact conversion.
Put it right: It is an approximation because the exact offset is 273.15.
Misunderstanding: the equation cannot be used for temperature differences.
Put it right: Because 1 °C equals 1 K, the same numerical difference applies.
Exam tips
- Write down the equation and substitute values carefully, checking the direction of conversion.
- Remember that the approximation is usually acceptable unless the question specifies otherwise.
- For temperature differences, no conversion factor is needed; the numerical value is the same in °C and K.
Try the lesson
The start of the Temperature: (d) T(K) ≈ θ(°C) + 273 lesson, made from checked teaching notes for this specification point.
Listen
The relationship T(K) ≈ θ(°C) + 273 allows you to convert a temperature from degrees Celsius to kelvin. Here, T is the thermodynamic temperature in kelvin and θ is the Celsius temperature. The approximation is used because the exact offset is 273.15, but for many calculations 273 is sufficient. For example, 20 °C is approximately 293 K. To convert from kelvin to Celsius, rearrange the equation: θ(°C) ≈ T(K) − 273. Always check the direction of conversion and whether the question expects the approximate or exact value. A strong answer earns marks for these points. The equation T(K) ≈ θ(°C) + 273 converts a Celsius temperature to kelvin. T represents the thermodynamic temperature in kelvin and θ represents the Celsius temperature. The approximation uses 273 instead of the exact 273.15. To convert from kelvin to Celsius, rearrange to θ(°C) ≈ T(K) − 273. A common slip: Misunderstanding: to convert from kelvin to Celsius, add 273. Instead, subtract 273, so θ(°C) ≈ T(K) − 273. Exam tip: Write down the equation and substitute values carefully, checking the direction of conversion.
See it
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