# A student is investigating how the temperature of water changes as it is heated on a hot plate. She measures the temperature every two minutes and records her results. She notices that the temperature stops rising for a period of time even though the hot plate is still switched on. Explain why the temperature of the water remains constant during this period, and describe what is happening to the water at this point.

> OCR A-Level Physics B: Advancing Physics (H557) — 1.1 Practical skills assessed · Explain · 5 marks

> A student heats a beaker of water on a hot plate. She records the temperature every two minutes. After some time, the temperature stops rising even though the hot plate remains switched on at the same power.

## Mark scheme (5 marks)

1. The water is changing state (from liquid to gas / boiling / evaporating)
2. The energy supplied by the hot plate is being used as latent heat
3. No energy is available to increase the kinetic energy of the particles
4. Temperature is a measure of the average kinetic energy of the particles, so if kinetic energy does not increase, temperature does not rise
5. Mass is conserved during the change of state (the mass of vapour produced equals the mass of liquid that evaporated)

## Key terms

- [temperature](https://www.gradenine.co.uk/glossary/temperature)

## Related

- [Revision notes for OCR A-Level Physics B: Advancing Physics (H557)](https://www.gradenine.co.uk/learn)
- [How to answer "Explain" questions](https://www.gradenine.co.uk/tools/command-word-cheatsheet)
- [Practice this with AI marking (free)](https://www.gradenine.co.uk/start)

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Source: [GradeNine](https://www.gradenine.co.uk/q/a-student-is-investigating-how-the-97b90dfd) · Published by Druglandscape Ltd.