The shape of the lesson
By the end of the lesson, learners can
- Slide between the scales: Move the temperature and watch the Celsius and kelvin readings change together.
- Converting, and the floor: Going from Celsius to kelvin is a single step, and the scale has a hard lower limit.
- Absolute zero: 0 K = -273 degrees C.
- Ice melts: 273 K = 0 degrees C. Water boils: 373 K = 100 degrees C.
- To convert: Celsius to kelvin, add 273. Kelvin to Celsius, subtract 273.
One picture every idea returns to
A temperature in kelvin equals the Celsius temperature plus 273. The kelvin scale begins at absolute zero (0 K, about minus 273 degrees Celsius), the lowest temperature possible, where the particles have their minimum energy.
Forty-five minutes, phase by phase
| Time | Phase | What happens in the room | Grouping |
|---|---|---|---|
| 0 to 5 min | Hook: predict | Open with the question in the title, Counting from absolute zero.. The Celsius scale was pinned to water: zero for freezing, one hundred for boiling. | Whole class, then pairs |
| 5 to 17 min | Teach and check: Slide between the scales | Move the temperature and watch the Celsius and kelvin readings change together. Project tab 6 of the lab (Temperature scales) and let a student drive it while the class predicts. | Whole class, then pairs |
| 17 to 30 min | Teach and check: Converting, and the floor | Going from Celsius to kelvin is a single step, and the scale has a hard lower limit. Model the worked example Worked example on the board, one line at a time. | Corners |
| 30 to 36 min | Check | The four Stage 1 questions from the student lesson, answered on mini whiteboards or by show of fingers. Re-teach the one most get wrong. | Individual, then whole class |
| 36 to 43 min | Plenary | The exam-style questions from Stage 2, one at a time: thirty seconds alone, then a random call. The feedback lines in the key give the examiner's wording. | Individual, random call |
| 43 to 45 min | Exit and homework | Set the worksheet below (6 questions, 12 marks). Learners self-assess against the objectives before they leave. | Individual |
Protect the parts that carry the learning
The sequence carries about fifty minutes of material, so the lab is driven by one student while the class predicts rather than explored freely. Times are a guide.
Protected: the check at 30 minutes. It is the only individual read on whether the key idea landed, and it is not cut.
Cut first if the build overruns: the last check in Converting, and the floor, never the check or the plenary.
In a 60 minute block: run worksheet questions 1 to 3 in class as a Rally Coach set and model both the hardest worked example and its check live.
Corners
Put one answer or viewpoint in each corner of the room. Students move to the corner they agree with, justify the choice to a partner there, then hear one voice from each corner before the reveal.
The full structure, with its variations and the other twelve, is on the cooperative-learning page.
What to head off, and how
| Trap learners fall into | Teaching move that pre-empts it |
|---|---|
| The kelvin scale starts at absolute zero, so a kelvin temperature can never be negative. | After converting, always check your answer is not below 0 K; if it is, something has gone wrong. |
Temperature scales (Celsius and kelvin): worksheet
6 questions, 12 marks. Written in the style of the papers; no past paper question is reproduced.
Convert the following temperatures:
(a) 80 degrees C into kelvin, [1] (b) 350 K into degrees Celsius. [1]State the value of absolute zero in degrees Celsius, and write the equation used to convert a Celsius temperature to a Kelvin temperature.
Describe what happens to the motion and energy of the particles of a substance as its temperature is lowered towards absolute zero.
Explain why it is not possible for a substance to have a temperature below 0 K.
On a cold night the temperature is -23 degrees C. A warm room is at 27 degrees C. Convert both temperatures to kelvin.
A student converts a temperature and writes the answer as -15 K. Without knowing the original temperature, explain how you can tell this answer must be wrong.
Answer key and marking notes
(a) 80 + 273 = 353 K
(b) 350 - 273 = 77 degrees C
- Absolute zero = -273 degrees C. ✓
- T (in K) = theta (in degrees C) + 273. ✓
- The particles move more and more slowly. ✓
- At absolute zero they have the least possible kinetic energy (effectively stop moving). ✓
- At 0 K the particles already have the minimum possible energy. ✓
- They cannot lose any more energy or move any more slowly, so no lower temperature is possible. ✓
Cold: -23 + 273 = 250 K
Warm: 27 + 273 = 300 K
- Kelvin temperatures cannot be negative, because 0 K (absolute zero) is the lowest possible temperature. ✓
- A value of -15 K is below absolute zero, which is impossible, so the student has made an error. ✓
2 multiple-choice questions on this lesson
From the topic question bank. Assign them in the app for a marked score in your gradebook, or run the topic as a class game.
A temperature of 27 °C is equal to how many kelvin?
- A246 K
- B254 K
- C300 K
- D327 K
What is the temperature of absolute zero on the Celsius scale?
- A0 °C
- B-100 °C
- C-273 °C
- D-373 °C
Quiz key
T(K) = 27 + 273 = 300 K. Option A subtracts instead of adds (273 − 27); D adds to the wrong base.
Absolute zero is 0 K, which is -273 °C, the temperature at which particle motion is at a minimum. Converting: 0 − 273 = -273 °C.
What to project
The student lesson embeds these tabs. Open them full screen on the projector; every slider has a drag handle on the stage.
Slides for this lesson
A projectable deck for every pack is on the way. Until then, present the student lesson full screen: its sections, figure and lab tabs follow the same order as the plan above.