5.1.4Light and the Electromagnetic Spectrum
Dangers of High-Energy EM Waves — Edexcel GCSE Combined Science 1SC0 - Physics Revision Notes & Topical Questions
5 min read 9 parts Lesson 5 of 8
Part 1 of 7Why EM radiation can be harmful
EM waves transfer energy to the material that absorbs them.
The harm depends on the energy of the waves, which increases with frequency, and on how much is absorbed.
Low-frequency waves mostly cause heating.
Ionise
High-frequency waves, UV, X-rays and gamma rays, can ionise atoms: they knock electrons out of atoms and molecules, which can damage cells and DNA.
Damaged DNA can cause mutations and cancer, or kill the cell.
Part 2 of 7Each part of the spectrum
Each part of the spectrum
Radio waves
Radio waves generally very low risk because of the low energy; strong radio sources can cause some heating.
Microwaves
Microwaves can heat the water in body cells.
- High exposure can cause internal burns.
- This is why microwave ovens have a metal mesh in the door and a switch that turns off the oven when the door opens.
- There is no clear evidence that mobile phone signals harm people, though some people suggest limiting phone use as a precaution.
Infrared
Infrared heats the skin and can cause burns when intense.
Visible light
Visible light bright light, such as from a laser or the Sun, can damage the retina.
Ultraviolet
Ultraviolet ionising to some extent; causes sunburn, skin ageing, eye damage and skin cancer.
X-rays and gamma rays
X-rays and gamma rays strongly ionising; can cause cell damage, cancer and, at high doses, radiation sickness.
Part 3 of 7Reducing the risk
Protection depends on the radiation:
1
Sunscreen and clothing absorb UV; sunglasses with a UV filter protect the eyes; limit time in the sun and avoid sunbeds.
2
For X-rays, radiographers stand behind lead screens or leave the room, use the smallest possible dose for the shortest time, and patients wear lead aprons to shield parts not being imaged.
3
Gamma sources are kept in thick lead containers and handled with tongs; workers wear film badges that record the dose.
4
Microwave ovens are shielded.
Part 4 of 7Risk and benefit
Radiation is used because its benefits outweigh its risks when it is controlled.
1
A chest X-ray exposes a patient to a small dose and may identify a serious condition.
2
Radiotherapy delivers a high dose to a tumour from several directions so that the tumour receives a lethal dose while healthy tissue receives much less.
3
Exposure of staff is limited by time, distance and shielding.
4
When evaluating a risk in an exam, compare the likely harm with the benefit, and say how the risk can be reduced.
Part 5 of 7Dose and ionisation
Ionising radiation has enough energy per photon to remove electrons.
1
UV at the high-frequency end, X-rays and gamma rays are ionising.
2
Non-ionising radiation (radio, microwaves, infrared, visible) has lower photon energy, so its main effect is heating.
3
A very intense source of low-energy radiation can still be dangerous because of heating, while a weak source of ionising radiation can raise the long-term risk of cancer.
4
The intensity, exposure time and the type of radiation all matter.
5
For uses see Applications of EM Waves and for radiation from nuclei see the radioactivity topics.
Part 6 of 7Comparing dangers in a table
| Radiation | Main effect on the body | Precaution |
|---|---|---|
| Microwaves | Internal heating of cells | Shielded ovens, interlocked doors |
| Infrared | Skin burns | Avoid hot sources, protective clothing |
| Ultraviolet | Sunburn, eye damage, skin cancer | Sunscreen, hats, UV-blocking sunglasses |
| X-rays | Cell damage, cancer | Lead aprons, short exposure, distance |
| Gamma rays | Cell damage, cancer, radiation sickness | Thick lead or concrete, tongs, badges |
In an examination, you may be asked to evaluate a claim such as "mobile phones cause cancer".
Comparing dangers in a table
A balanced answer states that mobile phones use microwaves, which are non-ionising and cannot directly damage DNA like ionising radiation, that large studies have so far not found a clear link, and that, since there is still some uncertainty, some people recommend using hands-free kits.
Scientists base conclusions on large samples and repeated, peer-reviewed studies rather than single reports.
Always finish an evaluation with a clear judgement and a reason, such as that the benefit of a medical X-ray outweighs the very small risk when it is needed to diagnose a serious condition.
Part 7 of 7Worked examples
Explain why UV radiation is more dangerous to skin cells than infrared.
UV has a higher frequency, so each photon carries more energy. It can ionise atoms and damage DNA in skin cells, possibly leading to skin cancer. Infrared mainly heats the skin.
A radiographer takes many X-ray images each day. State two precautions that reduce the dose she receives.
She can stand behind a lead screen (shielding) and keep the exposure time short or leave the room while the X-ray is taken. She can wear a film badge to monitor her exposure.
Key terms
| Term | Meaning |
|---|---|
| Ionising radiation | Radiation that can remove electrons from atoms |
| Mutation | Change in DNA that may lead to cancer |
| Film badge | Badge recording a worker’s radiation dose |
| Shielding | Material that absorbs radiation, e.g. lead |
| Dose | Amount of radiation energy absorbed |
Avoid these mistakes
1
Saying that microwaves are ionising – they heat but do not ionise.
2
Thinking all EM radiation is equally harmful.
3
Saying sunscreen blocks X-rays.
4
Forgetting to mention both time and shielding when listing precautions.
5
Saying that radio waves cause cancer by ionisation.
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