Electromagnetic Radiation – Summary Sheet
Type of Wave
Radio
Amanda George
Penetration
Uses
Micro
Page 1
Hazards
IR
UV
X-rays
Gamma
15/02/2016
Radio Waves
These have the longest wavelength of all electromagnetic waves, ranging from a
few centimetres to several kilometres or more. They also have the lowest energy.
Radio
Micro
IR
UV
X-rays
Gamma
Penetration:
Radio waves can pass easily through air. They can pass through many solids
(and, like all waves, they can also diffract around objects similar in size to, or
smaller than, their wavelength).
There is a high-altitude layer of the atmosphere, called the ionosphere, which
reflects longer wavelength radio waves rather than letting them pass through.
Uses:
Transmitting radio and television programmes across long distances: Radio
waves, like light waves, travel in straight lines, but…the Earth is curved. So
there’s a limit to how far round the Earth a radio wave can travel. However, the
ionosphere happens to reflect radio waves which are longer than about 10m, and
we can use this to send radio waves across greater distances.
Hazards:
None that we know of (which is lucky, since we are being bombarded by radio
waves all the time!)
Amanda George
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15/02/2016
Microwaves
These have wavelengths of around 0.1cm to 10cm.
Micro
Radio
IR
UV
X-rays
Gamma
Penetration:
Microwaves pass easily through air, and can pass right through the Earth’s
atmosphere. Microwaves are good for transmitting information from one place to
another because microwave energy can penetrate light rain, snow, clouds, and smoke.
Uses:
Cooking food: The microwaves are absorbed by water molecules in the food. The
energy carried by the waves turns into thermal energy in the food; in other words, the
food heats up.
Transmitter
Receiver
Mobile phones: These use longer
wavelength microwaves
(confusingly, these are sometimes
thought of as shorter wavelength
radio waves) to send signals
between your mobile phone and
antennas (base stations).
Sending signals to and from
satellites: This enables us to
transmit signals right across the
world, via satellites.
Hazards:
Microwaves can heat up water (as in your microwave oven), and our bodies contain a
lot of water, so microwaves can cause heating of body tissues. At the moment there is
some debate on whether or not microwaves from mobile phones and base stations are
hazardous to your health.
Protection: sheet metal, or a metal grid (mesh), will stop microwaves. You’ll notice a
mesh in the window of any microwave oven. It stops the microwaves from escaping
through the glass and harming you.
Amanda George
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15/02/2016
Infra-Red Waves (1)
These have wavelengths longer than the red end of visible light. The wavelengths
range between about 0.0007mm and 0.003mm.
Radio
Micro
IR
UV
X-rays
Gamma
Penetration:
Infra-red waves easily penetrate air, but are stopped by most solids. However, they
can penetrate glass (which is why you can still feel the sun’s heat through a car
windscreen).
Uses:
Night vision: Most objects emit (send out) infra-red radiation, and the hotter the object,
the more infra-red radiation it emits. We cannot see it, but we can make detectors
which can. These detectors are used in night-vision cameras or goggles, which can
show us what’s around even when there is no visible light for us to see by.
Cat in infrared light (converted to a
visible image your eyes can see).
Blue is colder, orange is hotter.
Amanda George
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Infra-Red Waves (2)
More Uses:
Security systems: These use infra-red cameras to spot intruders at night by the heat
of their bodies.
Remote controls: These send out infra-red waves, which are detected by the TV,
stereo or other device. Encoded into the waves are messages which tell the device
what to do. (By the way, remote controls use the shortest wavelengths of infra-red,
which do not heat things up very much – so your hand will not get warm if you aim
your remote control at it!)
Hazards:
Absorbed by the skin, which then heats up. This is why you feel warmer in direct
sunlight than in the shade. Too much infra-red radiation could give you skin burns
(although this is not common).
Did you know?
Humans may not be able to see infra-red waves, but did you know that snakes in the
pit viper family, like rattlesnakes, have sensory ‘pits’, which are used to see infra-red
waves? This allows the snake to detect warm blooded animals, even in dark burrows.
Amanda George
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Visible Waves
These have wavelengths of around 0.0004mm to 0.0007mm.
Radio
Micro
IR
UV
X-rays
Gamma
Penetration:
You will know from your own experience! What can light travel through, and what
does it take to block it?
Uses:
Our eyes use visible light to see by, of course. All of the electromagnetic spectrum is
invisible to us except for this tiny portion.
Cameras: These record images of how things appear in visible light. On a normal film
camera, the film is coated with chemicals which undergo chemical reactions when
exposed to light.
Digital cameras use a detector to record the image electronically. The camera’s
processor (a mini computer) then breaks this electronic information down into digital
data. Essentially, a digital image is just a long string of 1s and 0s that represent all the
tiny coloured dots -- or pixels -- that collectively make up the image.
Hazards:
None.
Amanda George
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15/02/2016
Ultra-Violet Waves (1)
These have wavelengths of around 0.00001mm to 0.0004mm.
Radio
Micro
IR
UV
X-rays
Gamma
Penetration:
Ultra-violet waves cannot penetrate most solid materials. For example, they cannot
penetrate glass (which is why you won’t get a sunburn through a closed window).
They also do not penetrate clothing very much (except for very thin fabrics).
Ultra-violet waves can penetrate air easily, except for a high layer of the Earth’s
atmosphere called the ozone layer, which blocks a lot (though not all) of the ultra-violet
radiation from the sun. You may have heard that the ozone layer is getting thinner,
which means that we are being exposed to more ultra-violet radiation.
Uses:
Sunbeds: Ultra-violet waves are what cause our skin to tan or burn. Sunbeds use
ultra-violet lamps to give you a tan without having to wait for the sun to come out.
Detecting forged bank notes: To make them more difficult to forge, real notes have some patterns or marks
on them made with fluorescent dyes. These dyes cannot be seen in visible light, but if you shine ultra-violet light on them,
they convert energy in they ultra-violet radiation into visible light. This is called fluorescing.
An American 20-dollar
note, in visible light (left)
and ultra-violet light
(right). Note the
fluorescent strip which
only shows up in ultraviolet light.
Amanda George
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Ultra-Violet Waves (2)
Security coding: An identity code can be written onto a valuable item in fluorescent
ink. The code is invisible under normal light, but the police can read it under an ultraviolet light. Stolen goods can be identified by their codes and returned to their original
owners.
Hazards:
Ultra-violet radiation can be quite dangerous. Stay in the sun too long and your skin
will burn. The damage can affect the way your skin cells function – in particular how
they divide to make new cells – and too much exposure to ultra-violet light may lead to
skin cancer later.
Too much ultra-violet light can, in the long term, damage your eyes – in particular, the
layer of cells at the back (called the retina) where the image appears.
Protection:
Sunscreen is designed to block ultra-violet light, stopping it from reaching your skin.
No sunscreen blocks all ultra-violet light though, so you should still be careful not to
stay out in the sun too long.
Have you noticed that a lot of sunglasses are labelled ‘UV protection’? They have a
special coating which blocks ultra-violet light (unlike the plastic the lenses are made
from).
Did you know?
When we use special cameras to look at flowers in ultra-violet light, we often find
patterns that can’t be seen in visible light. It turns out that bees can see ultra-violet
light and are probably guided to the flowers by these patterns, which are invisible to
our eyes.
flower in
visible light
same flower in
ultra-violet light
(but converted
here to a visible
image so we can
see it!)
Amanda George
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X-Rays
These have very short wavelengths and very high energies. X-rays are a type of
‘ionising radiation’, which means radiation that can actually alter matter (by knocking
electrons out of atoms).
Radio
Micro
IR
UV
X-rays
Gamma
Penetration:
X-rays are quite penetrating. They pass through air very easily, as well as low-density
solids such as body tissue. They are partially stopped by bone and thin metal.
Uses:
X-ray machines: These are used to make pictures of your
bones, to reveal fractures. This works because x-rays pass
fairly easily through most body tissue, but not through bone.
So in an x-ray image, silhouettes of the bones are left on the
film, while the rest of your tissue appears almost transparent.
Hazards:
Too much exposure to x-rays can damage the cells of your
body, and may result in cancer later.
Protection:
It takes a sheet of lead several millimetres thick to stop x-rays completely.
Did you know?
A German scientist, Wilhelm Conrad Roentgen, discovered x-rays in 1895. He initially
called them ‘X’ to indicate that they were an unknown, mysterious type of radiation.
The name stuck.
Amanda George
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15/02/2016
Gamma Rays
These have the shortest wavelength of all electromagnetic waves. They also have the
highest energy. There are not many things that emit gamma rays, but some
radioactive materials do. Some extreme objects in space also emit gamma rays; one
example is a supernova, or exploding star.
Radio
Micro
IR
UV
X-rays
Gamma
Penetration:
These are the most penetrating of all types of electromagnetic radiation. They can
pass straight through your body, for example.
Uses:
Sterilising food and medical
equipment: Because gamma rays
can kill living cells, they can be used
to destroy bacteria, mould or insects
on food or medical equipment.
Treatment of cancers: Cancer cells can be killed by gamma rays. This treatment is
called radiotherapy. However, gamma rays also kill healthy cells, so the treatment has
to be carefully designed to target the cancer cells only.
Hazards:
Reasonably safe in low doses, as they pass straight through your body without being
absorbed much. However, high exposures can kill living cells.
Protection: it takes a lot to stop gamma rays! You need several centimetres of lead, or
thick concrete.
Amanda George
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15/02/2016