# A hospital uses two types of medical warming blankets to keep patients comfortable during recovery. Blanket X has a power rating of 60 W and Blanket Y has a power rating of 90 W. Both blankets are connected to the mains supply, which provides the same potential difference across each blanket. Explain why Blanket Y transfers more energy to a patient than Blanket X when both are switched on for the same amount of time, and describe what this means for the current flowing through each blanket.

> OCR A-Level Physics A (H556) — 3.3 Work, energy and power · Explain · 5 marks

> Both blankets are connected in parallel to the same mains supply and operate for the same duration.

## Mark scheme (5 marks)

1. Power is the rate at which a device transfers energy
2. Blanket Y has a higher power rating so it transfers more energy in the same time
3. Energy transferred equals power multiplied by time, so greater power gives greater energy for the same time
4. Both blankets have the same potential difference across them (connected in parallel to the same supply)
5. Since power = current × voltage and voltage is the same, Blanket Y must carry a greater current than Blanket X

## Key terms

- [power](https://www.gradenine.co.uk/glossary/power)
- [potential difference](https://www.gradenine.co.uk/glossary/potential-difference)
- [current](https://www.gradenine.co.uk/glossary/current)
- [energy](https://www.gradenine.co.uk/glossary/energy)

## Related

- [Revision notes for OCR A-Level Physics A (H556)](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)

---
Source: [GradeNine](https://www.gradenine.co.uk/q/a-hospital-uses-two-types-of-3487a616) · Published by Druglandscape Ltd.