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Electromagnetic Radiation and Light

X-Ray of a hand

Elecromagnetic radiation

Elecromagnetic radiation includes light, ultra violet, infra red, radio waves, X rays, gamma rays, microwaves and other forms of radiation all have different wavelengths and have very different but important impacts in our world. Let us look at these different forms of radiation, their frequencies and how they are important in our lives.

In other articles on this site we have talked about electro magnetism and the part it plays in generating and using electricity, we have also looked at why Nuclear Power stations make bad neighbours. This week we will look at something related to both, something that we are all surrounded by, enveloped in and even penetrated by. Something that makes life possible as we know it. No I am not talking about horizontal leisure activities or even Dunkin Donuts, I am talking about electro magnetic radiation.

“Oh no” I hear you think, not another boring diatribe that even Albert Einstein would find somewhat tedious. Well I'm sorry, sit down, take a deep breath and prepare to be tedied.

Waves and wavelength

Let us start by imagining that Albert Einstein is standing on the side of a pond. If he throws a pebble into the pond and, while he is contemplating whether e=mc2 is valid when applied to the curdling of milkshakes, he notices that the stone splashing into the water causes a disturbance which forms waves that radiate out in an ever widening circles from the centre and splash over his foot. At any point the water moves up and down while the waves travel horizontally across the surface of the water.

If we have bigger waves the distance between their crests (the wavelength) is longer while the speed at which they travel across the water remains the same.

Now imagine if we make the waves very, very small, as the size of each wave gets smaller the number of waves (the frequency) increases.

Sound waves

Sound, of course, works in this way. At night the friendly greeting from that dog next door creates a very welcome disturbance to our sleep but in this case, rather than ripples in water, it creates ripples of high and low pressure in the air. These ripples hit our ear as sound. As we all know sound travels at a fixed speed of 340.29 metres per second (that's pretty quick, in fact it's nearly as fast as a Legian money changer can remove the money from your wallet). Big ripples make deep sounds and, if the ripples get smaller, as the distance between them gets shorter so the number that hit our poor long suffering ear drums every second (the frequency) increases and the sound we hear is higher pitched.

Yes I know, we all know this and my grandmother learned to suck eggs some time ago. But now let us consider the same effect with electromagnetic energy.

Light and photons

The photon is the basic unit of light and all other forms of electromagnetic radiation. It is thought to be either a subatomic particle or a discrete bundle of electromagnetic (light) energy. This stuff is not fully understood and even Einstein got a headache thinking about it, the stress turned his hair curly.

Photons behave like particles but they also behave like waves of energy and they carry electromagnetic force. The energy and momentum that photons exert depends on the frequency of their waves. Just like sound, electromagnetic energy travels at a fixed speed (the speed of light) a mere 186,282 miles per second which, believe it or not, is even faster than that ever so friendly Legian money changer can remove the money from your wallet.

In our daily lives we are constantly being bombarded by waves of electromagnetic force, most of these waves are harmless while others can certainly give us a bad day. It is all determined by the frequency of the waves, the more frequent and the more penetrating and destructive. Different forms of electromagnetic radiation are known by different names but in fact are just different frequencies of the same thing. The following table indicates different forms of electromagnetic radiation and what we use them for:

Different forms of electromagnetic radiation

Type of radiation



Ionising radiation

Gamma Rays

>10 Exahertz

Scanning of Shipping containers,irradiation sterilising, treatment of cancer, nuclear medicalimaging, causing cancer and deforming bodyparts.

X rays

30 Petahertz to 30 Exahertz

Medical imaging, treatment of cancer, industrial inspection, intimate entertainment for airport security staff.

Ultraviolet light

750 THz to 30 Petahertz

Fluorescent lamps, sterilisation,security systems, disco lights, sun tanning, fire detection, skin cancer.

Non Ionising radiation

Violet light

665 to 715 THz

Vision, rainbows, election finger marking

Blue light

610 to 680 THz

Vision, rainbows, lovesickness.

Green light

525 to 575 THz

Vision, rainbows, vegetarian food.

Yellow light

515 to 525 THz

Vision, rainbows, nice sunsets, jaundice.

Orange light

485 to 510 THz

Vision, rainbows, flames.

Red light

405 to 480 THz

Vision, rainbows, traffic lights

Infrared 1 to 430 THz THz is also known as Tremendously High Frequency Remote temperature sensing, night vision, heat seeking missiles, television remote controls, astronomy, weather forecasting, keeping inedible chiko rolls luke warm.
Microwaves SHF and EHF 300 MHz to 300GHz Super High Frequency and Extremely High Frequency Long distance telephone communication, radar, speed cameras, bluetooth, broadcasting, telecommunications, cooking your tea and killing grandma's cat.
UHF Television 300 MHz to 3 GHz Ultra High Frequency Television broadcasting, 2 way radio systems, cordless telephones. Car remote locking systems. Small antennas needed but line of sight broadcast.
VHF Television 30 to 300 MHz Very High Frequency Television broadcasting, digital audio broadcasting, air navigation beacons, air traffic control and instrument landing systems.
FM radio 87.5 to 108 MHz Frequency Modulated High fidelity radio broadcast.
CB (citizen's band) radio 27 MHz “Wot's yer 'andle?” (not much else really)
Shortwave AM radio 1711 to 30 MHz
Amplitude Modulated
Radio broadcasting
Mediumwave AM Radio 520 to 1610 kHz Most AM radio broadcasting
Longwave AM Radio 148.5 to 283 kHz Long distance radio transmissions.

1 Hz = 1 Hertz or one cycle per second.
1 khz = kilohertz or 1,000 cycles per second,
1 MHz = Megahertz or 1,000,000 cycles per second
1 GHz = Gigahertz or 1,000,000,000 (American billion) cycles per second,
1 THz = Terahertz or 1,000,000,000,000 (British billion, American trillian) cycles per second
1 PHZ = Petahertz or 1,000,000,000,000,000 cycles per second
1 EHz = Exahertz or 1,000,000,000,000,000,000 (British trillion) cycles per second

If we look at the above table we see how important electromagnetic radiation is to our daily lives. I ask you, how could normal life continue without the humble remote control? We can also see that there are two important change points as the frequency increases.

Microwaves can be dangerous

The first is when the frequency reaches microwave frequencies. At these frequencies the electromagnetic radiation is powerful enough to start molecules of water and fat vibrating which produces heat. By blasting microwaves through our food it cooks it right through and this is, of course, why grandma should not put her cat in the microwave, it dries the cat out but also has a tendency to boil its blood and cook its innards at the same time.

This tendency for microwaves to "cook" things is why there are concerns about microwave communication towers and has also lead people to believe that mobile phones and the microwaves they transmit next to your head can affect your brain. It is known that microwaves can cause cataracts. It is understandable why people who work on aircraft carrier decks wear protective suits to protect them from the powerful microwaves of the radars on both the planes and the aircraft carrier itself.

It is a good idea to keep away from microwave ovens while using them. You might also like to note that microwaves travel through things like paper, wood, plastics, flesh, etc. but not through metal.

The second change point is far more sinister. It is the point where electromagnetic radiation is powerful enough to break down molecular structures.

Ultra Violet UV light

The lower end of this frequency band is where we get into Ultra Violet (UV) light which can damage living cells and of course causes skin cancer. UV is used to sterilise water (by killing cells). It also breaks down polymers in plastics which is why plastics, paints and varnishes deteriorate in full sunlight. Protection of plastics is achieved by adding colour pigments that block the UV light. Grey gutters and plumbing pipes have pigment added and are UV resistant. UV also has the ability to agitate teenagers in discotheques.

X rays

Above UV we get into X-Rays and we all know about the dangers of them. At frequencies above this we start getting into the real nasty stuff, gamma radiation.


Full sunshine consists of 52.7% infrared radiation, 44.5% visible light and 3.2% ultraviolet radiation.

Copyright © Phil Wilson May 2011
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