The Electromagnetic Spectrum
Light waves are not only made up of the light that we can see (visible light) but also other types of radiation - gamma, X-ray, ultraviolet, infrared, microwaves and radiowaves. These are organised along a spectrum known as the electromagnetic spectrum.
Electromagnetic radiation
There are seven different types of electromagnetic radiation which are organised along a spectrum. All of the EM waves are transverse waves and they all travel at the same speed through space (i.e. the same speed in a vacuum). You need to remember the order of the spectrum and it helps a lot to use a mnemonic such as ‘Red Martians Invade Venus Using X-ray Guns’, or my personal favourite, ‘Ripped Men In Violet Underpants (are) eXtremely Gorgeous’. Radio waves have the longest wavelength but the shortest frequency and gamma waves have the shortest wavelength but the highest frequency.
Uses of electromagnetic waves
EM waves are pretty useful – it turns out you have them to thank for lazing about watching TV while eating a plate of microwave carbonara. Some specific uses of different EM waves are listed below:
Radio Waves: this type of wave has the longest wavelength so they are good at transmitting information long distances. Radiowaves are used for TV and radio broadcasting.
Microwaves: microwaves are used for satellite TV and mobile phone communications. They’re also used in microwave ovens to heat up food.
Infrared radiation: infrared radiation is basically heat. It is the signal detected by night-vision equipment when police are trying to find an escapee in the dark. It’s also used by heating devices, such as electric heaters and grills.
Visible light: of course we need visible light just to see our surroundings, but visible light can also be used for communication using optical fibres and photography.
Ultraviolet: fluorescence occurs when a fluorescent material absorbs UV light and emits visible light in response. UV light is used for things like fluorescent lamps and detecting forged banknotes. It’s the type of radiation emitted naturally by the Sun and artificially by sunbeds.
X-ray: X-rays allow us to see the internal structures of objects so are useful for detecting broken bones and fractures.
Gamma radiation: Gamma radiation is at the end of the spectrum and has the highest frequency. Exposure to gamma radiation is effective at killing microbes so it is used to sterilise food and medical equipment.
Dangers of Electromagnetic Waves
Small amounts of exposure to electromagnetic waves is harmless, however repeated exposures to large doses of EM waves can have serious consequences to our health. For instance, hanging out in the sun every so often won’t hurt you but lying underneath the blazing heat without suncream on Spanish beaches could lead to sunburn and skin cancer. In general, the low frequency EM radiation (radiowaves, microwaves) is much less harmful than the EM waves with higher frequencies (X-ray and gamma). The list below describes the possible negative consequences of different types of EM waves and the ways we can protect against them:
Microwaves: just like how microwaves heat up food by warming up food from the inside, microwaves do the same thing to our cells. Internal heating of our body tissue is dangerous so microwave ovens have a coating to shield the waves from the user.
Infrared: excessive exposure to infrared radiation can cause skin burns and in more extreme cases, skin cancer. Insulating materials can be used to protect against the effects of infrared radiation.
Ultraviolet: UV radiation can cause damage to surface cells and blindness. When they enter cells they can mutate the DNA which leads to cancer. Suncream is used as a protective measure to reduce exposure to UV.
Gamma: gamma radiation can penetrate cells and mutate the DNA, leading to tissue damage or cancer. People who have to work with gamma radiation, such as doctors, will limit the amount of time they are exposed. The sources of gamma rays are also kept in a box lined with lead.