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Unlock This CourseIn Uses of Electromagnetic Waves you saw how much we rely on electromagnetic radiation. The same waves can harm the human body if we get too much of them. The spec calls this excessive exposure, and the harm it does is a detrimental effect.
Notice the word excessive. A small amount of most radiation does little or no harm. The risk grows when the radiation is strong, when you are close to the source, or when you are exposed for a long time.
All electromagnetic waves transfer energy. When the body absorbs a wave, that energy is transferred to the body's cells. What happens next depends on the type of wave, so you need to learn four of them in detail.
Key terms:
Remember the order of the electromagnetic spectrum: radio waves have the lowest frequency and gamma rays have the highest. The higher the frequency of the radiation, the more energy it carries. More energy means it can do more damage to the cells of the body.
This gives a simple pattern:
Radio waves have the lowest frequency of all and carry the least energy, which is why they are not on the list of dangers you need to learn. X-rays sit next to gamma rays in the spectrum and cause the same kinds of harm as gamma rays.
| Radiation | Detrimental effect | Simple protective measures |
|---|---|---|
| Microwaves | internal heating of body tissue | metal mesh screen in the door and metal walls of a microwave oven |
| Infrared | skin burns | insulated gloves, heat shields, keeping your distance |
| Ultraviolet | damage to surface cells and blindness | sun cream, clothing, sunglasses, shade |
| Gamma rays | cancer, mutation | lead shielding, distance, short exposure times |
Microwaves pass through the skin and are absorbed by water in the tissue underneath. Body tissue contains a lot of water, so the tissue heats up from the inside. This is internal heating of body tissue, and it can damage or kill cells deep in the body.
Infrared is absorbed at the surface of the body, so it heats the skin. You feel this as warmth. Too much infrared heats the skin so strongly that the cells are damaged, causing skin burns.
The difference is where the heating happens. Infrared heats the surface, and you feel it at once and pull away. Microwaves heat tissue below the surface, where damage can begin before you feel much on your skin.
Protection from microwaves. A microwave oven is a metal box. Its walls reflect microwaves and keep them inside. The glass door has a metal mesh screen built into it. The holes in the mesh are much smaller than the wavelength of the microwaves, so the microwaves are reflected back into the oven. Visible light has a far shorter wavelength, so it passes through the holes and you can still see your food. The oven also switches off as soon as the door is opened.
Protection from infrared. A baker lifting trays out of a hot oven wears insulated gloves. A firefighter wears thick insulated clothing and a helmet with a visor that acts as a shield. Shiny shields work well because they reflect infrared. Moving further from the hot object also helps, because the radiation is weaker further away.
Ultraviolet has a higher frequency than visible light, so it carries more energy. The Sun is our main source, and sunbeds also emit it. Ultraviolet is absorbed in the outer layers of the body, and it harms us in two ways.
You cannot see ultraviolet or feel it as heat, so you can be harmed on a cool, cloudy day without noticing. Snow, sand and water reflect it, so skiers and sailors receive more than they expect.
Absorbs or reflects ultraviolet before it reaches the skin cells.
Long sleeves and a hat cover the skin, so much less ultraviolet reaches it.
Absorb ultraviolet so that it does not reach the eyes.
Staying in the shade when the Sun is strongest, and spending less time in the Sun, also reduce the exposure.
Gamma rays have the highest frequency in the spectrum, so they carry the most energy. They are also very penetrating. They pass through the skin and are absorbed by cells deep inside the body.
When a cell absorbs a gamma ray, the energy can damage the genetic material in the cell. This change is a mutation. A mutated cell may die, or it may start to divide in an uncontrolled way. Uncontrolled cell division is cancer.
People who work with gamma rays, such as hospital staff, use three simple protective measures:
You will meet these ideas again, in more detail, in Dangers of Ionising Radiation.
Question: A glass-blower works close to a furnace that emits infrared. Explain one risk to the glass-blower and one protective measure. [3 marks]
Answer: Infrared is absorbed by the skin and heats it (1), which can cause skin burns (1). The glass-blower should wear insulated gloves when working near the furnace (1).
A full answer names the radiation, says what it does to the body, then gives a protective measure that matches that radiation.
Electromagnetic waves are useful, but excessive exposure can harm the human body.
(a) State the detrimental effect of excessive exposure to microwaves. [1 mark]
(b) Explain why the door of a microwave oven contains a metal mesh screen. [2 marks]
(c) A lifeguard works outdoors on a beach all day.
(i) State two detrimental effects of excessive exposure to ultraviolet. [2 marks]
(ii) Describe two simple protective measures the lifeguard should take. [2 marks]
(d) Explain why gamma rays are more dangerous to the human body than radio waves. [3 marks]
(a) Internal heating of body tissue (1).
(b) The metal mesh reflects the microwaves (1), so they stay inside the oven and do not reach the person using it (1).
(c)(i) Damage to surface cells of the skin (1). Blindness, or damage to the eyes (1).
(c)(ii) Any two from: wear sun cream (1), cover the skin with clothing or a hat (1), wear sunglasses (1), stay in the shade (1).
(d) Gamma rays have a much higher frequency than radio waves (1), so they carry more energy (1). This energy can damage cells, causing mutation or cancer (1).
In part (c), "state" needs only the effect, but "describe" needs a clear action, so write "wear sunglasses to protect the eyes" and not just "protection". In part (d), three marks means three linked steps: higher frequency, more energy, then the named damage.