A security system at an art gallery uses infrared sensors to detect intruders in the dark. Explain why infrared radiation is suitable for this purpose, and describe one other use of infrared radiation in everyday life.

OCR GCSE Physics A: Gateway Science (J249) — P4.2 The electromagnetic spectrum · Explain · 4 marks · View as Markdown

Written & reviewed by James Millett — Biology (Imperial College London), PGCE Science (University of Cambridge).

Art galleries often need to protect valuable paintings overnight without using visible light, which could damage the artworks. Security engineers install sensors that detect radiation emitted by warm objects.

Model answer (4 marks)

All objects above absolute zero emit infrared radiation.
Infrared radiation can be detected in the absence of visible light, so the sensor works in the dark.
A common everyday use of infrared is in remote‑control devices.
In a remote, the infrared LED emits pulses that are received by a photodiode in the appliance, allowing the user to control it without visible light.

Examiner tips

  • Use the exact phrase ‘infrared radiation’ and ‘infrared LED’. Show the link between emission and detection in the dark. Give a clear example and explain the basic principle of the application.

Common mistakes

  • Confusing infrared with visible light. Giving a non‑infrared example such as radio waves. Omitting the explanation of how the remote works.

Mark scheme (4 marks)

  1. All objects (above absolute zero) emit infrared radiation
  2. Infrared radiation can be detected in the absence of visible light / the sensor detects infrared without needing the room to be lit
  3. A named everyday use of infrared radiation
  4. Correct description of how infrared is used in that named application

Key terms in this question

infrared radiation

Related

More The electromagnetic spectrum questions

▶ Try answering this question with AI marking (free) →