Matter: Hot or Cold | OCR A-Level Physics B (Advancing Physics) (H557)
Matter: Hot or Cold
- 61 questions
- 4 subtopics
- The physics content, examined on all three papers
- Component 01, Component 02 and Component 03
Matter: Hot or Cold is examined in all three written papers — the specification states that Components 01, 02 and 03 each assess content from across all the teaching modules, so nothing is confined to one paper.
It covers energy, temperature and the ratio E/kT, the Boltzmann factor and populations of energy states, graphs of the Boltzmann factor and activation processes and the effect of temperature.
Sample questions from Matter: Hot or Cold
Answer each one closed book first, then open the answer.
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Energy, temperature and the ratio E/kT
An energy step of 6.4 × 10⁻²⁰ J exists at 290 K. Calculate E/kT.
Show the answer
kT = 1.38 × 10⁻²³ × 290 = 4.0 × 10⁻²¹ J, so E/kT = 16. -
Energy, temperature and the ratio E/kT
Water has a specific latent heat of vaporisation of 2.3 × 10⁶ J kg⁻¹ and a molar mass of 0.018 kg mol⁻¹. Estimate the energy needed for one molecule to escape.
Show the answer
One mole needs 2.3 × 10⁶ × 0.018 = 4.1 × 10⁴ J, so one molecule needs 4.1 × 10⁴ ÷ (6.02 × 10²³) = 6.8 × 10⁻²⁰ J. -
The Boltzmann factor and populations of energy states
An energy step of 6.4 × 10⁻²⁰ J exists in a material at 290 K. Calculate the Boltzmann factor.
Show the answer
kT = 4.0 × 10⁻²¹ J, so E/kT = 16 and the factor is e⁻¹⁶ = 1.1 × 10⁻⁷. -
The Boltzmann factor and populations of energy states
A process requires 0.50 eV. By what factor does its Boltzmann factor rise when the temperature goes from 300 K to 310 K?
Show the answer
E/kT falls from 19.3 to 18.7, so the factor rises by e⁰·⁶², about 1.9, roughly doubling. -
Graphs of the Boltzmann factor
Describe the shape of a graph of the Boltzmann factor against temperature at a fixed energy.
Show the answer
It is almost zero at low temperatures, rises steeply once kT becomes comparable with the energy, then flattens as it approaches one. -
Graphs of the Boltzmann factor
Two materials with different activation energies are plotted as ln(rate) against 1/T. How do their lines differ?
Show the answer
The material with the larger activation energy gives the steeper negative gradient. -
Activation processes and the effect of temperature
Explain why a thermionic cathode must be run at over a thousand kelvin.
Show the answer
The work function is a few electronvolts, well over a hundred times kT at room temperature, so a very high temperature is needed before the Boltzmann factor becomes appreciable. -
Activation processes and the effect of temperature
Explain why the viscosity of a liquid falls as it is heated.
Show the answer
Molecules need an activation energy to slip past their neighbours, and at higher temperature far more of them have it, so the liquid flows more easily.
The 4 subtopics
One subtopic is one session. Work down the list.
| Subtopic | What it covers | Questions |
|---|---|---|
| Energy, temperature and the ratio E/kT | Recall questions on kT and its size at room temperature, comparing bond, band-gap and escape energies with it, why the ratio has no unit, and what a small ratio implies. | 15 |
| The Boltzmann factor and populations of energy states | Recall questions on the Boltzmann factor e^(−E/kT) and why it is below one, its value when the step is kT or 10kT, calculating factors and populations, its limits at very high temperature and near absolute zero, why a small temperature rise matters so much, the classical approximation, finding an activation energy from rates, and states of equal energy. | 15 |
| Graphs of the Boltzmann factor | Recall questions on its shape against energy and against temperature, why it never exceeds one, which logarithmic plots straighten the data, their gradients and intercepts, and obtaining an activation energy. | 15 |
| Activation processes and the effect of temperature | Recall questions on activation energy and why activated processes speed up sharply with temperature, evaporation and evaporative cooling, thermionic emission and hot cathodes, ionisation in stars, semiconductor and metal resistance, viscosity and cold engine oil, melting over a narrow range, and why refrigeration slows food spoiling. | 16 |
How the guide is worked
Answering a question from memory stores it far better than reading the answer again. The guide runs that as a fixed procedure on one subtopic at a time, about twenty minutes a session.
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Step 1 · Closed book
Cover the answers. Work through one subtopic and write down what you can. Leave blanks where you have nothing.
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Step 2 · Open book
Go back to the top. Read each printed answer and write it out in full, including the ones you had right.
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Step 3 · Closed book again
Same questions, same order, from memory. The gap between pass one and pass three is the session result.
Read the full method, the return schedule and the research behind it.
Nearby topics
OCR A-Level Physics B (Advancing Physics) Active Recall Guide
Every topic, not just this one. 2,455 questions with their answers.