A student is comparing the uses and dangers of ultraviolet (UV) radiation and X-rays. The student claims: 'Both UV radiation and X-rays are dangerous, but for exactly the same reasons and to the same degree.' Explain whether the student's claim is correct, referring to the uses of both types of radiation and the dangers each poses to the human body.

Edexcel A-Level Physics (9PH0) — 5.2 Quantum physics · Explain · 5 marks · View as Markdown

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

UV radiation and X-rays are both part of the electromagnetic spectrum. UV radiation has a lower frequency than X-rays.

Model answer (5 marks)

Both UV radiation and X‑rays can damage cells, but the damage differs.
1. UV has lower frequency and energy, so it mainly affects surface tissues – skin and eyes – causing sunburn, skin cancer and cataracts.
2. X‑rays have higher frequency and energy, allowing them to penetrate deeper; they can mutagenise internal cells and increase the risk of cancer.
3. Because X‑rays carry more energy, they are generally considered more dangerous per unit exposure.
4. UV is used for disinfection (water, surfaces) and in fluorescent lighting.
5. X‑rays are used for medical imaging (radiographs, CT) and security scanning.

Thus the student’s claim is incorrect: the reasons and severity of danger differ, and the uses are distinct.

Examiner tips

  • Use the word ‘penetrate’ for X‑rays, ‘surface’ for UV; mention skin/eyes vs internal cells.
  • Show the energy difference by citing higher frequency of X‑rays.
  • Separate uses clearly: disinfection vs imaging.
  • Include the specific health risks for each type.

Common mistakes

  • Saying both have identical dangers; ignoring depth of penetration.
  • Confusing UV with visible light; not mentioning energy difference.
  • Mixing up uses (e.g., claiming UV is used for imaging).

Mark scheme (5 marks)

  1. The student is partially correct — both UV and X-rays are dangerous electromagnetic waves that can damage cells
  2. UV radiation causes damage to surface cells and eyes, which can lead to skin cancer and eye conditions
  3. X-rays can cause mutation or damage to cells deeper inside the body, and can cause cancer
  4. X-rays have a higher frequency than UV, so they carry more energy and are more penetrating / more dangerous
  5. The uses of UV and X-rays are different — UV is used for disinfecting water and fluorescent lamps, whereas X-rays are used for medical imaging / airport security scanners

Key terms in this question

ultraviolet · X-rays

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