This topic accounts for approximately 14% of your exam marks.
stable
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Stable14%
Wave equation (v = fλ), transverse vs longitudinal and EM spectrum properties tested consistently.
The general rule
Going left to right across the spectrum, wavelength shortens and frequency rises, and so does the energy per photon
Beyond the visible band the energy becomes large enough to ionise atoms (knock electrons off them); ionising radiation can damage DNA and kill living cells
The further into the short-wavelength end of the spectrum, the more damaging the radiation: ultraviolet < X-rays < gamma rays
Specific hazards by band
Microwaves: at high intensity they can heat internal body tissue (the same effect as inside a microwave oven). Modern phones and ovens are designed so that levels at the user are far below the heating threshold
Infrared: strong infrared can burn the skin, just as touching a hot stove would. This is why grills and heaters are guarded
Ultraviolet: over-exposure causes sunburn in the short term and skin cancer in the long term; it can also damage the retina if shone directly into the eye, and in extreme cases cause blindness
X-rays and gamma rays: kill cells outright (useful in radiotherapy, dangerous to healthy tissue) and damage DNA, increasing the risk of cancer and genetic mutations
Safety measures
Microwave ovens: the metal walls and the wire-mesh grid in the door reflect microwaves back into the cavity; the oven also switches off as soon as the door is opened
Infrared heaters and grills: protective gloves and screens, kept-out distances, and clear warning labels
Ultraviolet (sun and sunbeds): sunscreen with a high SPF absorbs UV before it reaches the skin; UV-blocking sunglasses protect the eyes; outdoor workers wear long-sleeved clothes
X-rays in hospitals: only the smallest dose needed for the image is used; radiographers leave the room (or sit behind a lead screen) when the X-ray is fired; pregnant women are not given X-rays except for essential reasons
Gamma-ray workers: those who routinely handle radioactive sources wear film or thermoluminescent badges that record their cumulative dose, and their total dose over the year is monitored by an occupational-health team