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White light can be split up into lots of different coloured light waves using a prism. We call this range of colours the visible spectrum, however, this is only a small part of a very much longer spectrum called the electromagnetic spectrum. Humans can only see the visible part of the spectrum; the rest of the electromagnetic spectrum is invisible to the human eye. Other animals are able to detect other parts of the spectrum that human' s cannot see, for instance the infrared and ultraviolet waves.
All the parts of the electromagnetic spectrum can be reflected, refracted and diffracted which shows that each part is a type of wave. In fact, the electromagnetic spectrum is a whole continuous family of waves. They are all transverse waves. They all travel at the same speed through space. This speed is 300,000,000 m/s (the speed of light) this can also be written as 300 thousand km/s.
Electromagnetic waves do not need a medium (matter) to travel in. They can travel through space. This is fortunate as we get most of our energy from the sun as electromagnetic waves.
Although all the waves in the spectrum have the same speed, each type has its own range of frequencies and wavelengths. The difference in the frequencies gives each type of wave its own characteristics, for example, in the visible spectrum each different frequency has a different colour.
You will need to know the order of the spectrum. Remember gamma waves are at the high frequency end of the spectrum and radio waves are at the low frequency end.
Each type of wave in the spectrum has its own use. You will need to know the possible uses and dangers of each type of wave. Move the mouse over the spectrum to see the information about each wave:
The higher frequency radiations (U.V. X-rays and gamma waves) are the most dangerous. Low doses can cause normal cells to become cancerous. Higher doses will kill cells. This is because these types of radiation cause ionisation.
You should be able to describe ways of reducing the amount of radiation absorbed by people. The main safety points are:
- Point radiation sources away from people.
- Wear lead lined clothing (lead absorbs more radiation than most other materials).
- Wear gloves and use tongs when handling substances that emit radiation.
Why do different objects look different colours?
Each surface absorbs and reflects different frequencies of light. White surfaces reflect all colours. Black surfaces absorb all colours. Some people argue that black isn't really a colour at all; it's a lack of colour as all the light has been absorbed.
When any radiation is absorbed its energy is changed into heat energy. This means that black objects that absorb radiation easily heat up quickly, whereas white objects reflect the radiation so stay cooler.
A blue object reflects blue light and absorbs all the others. A red object reflects red light and absorbs the others and so on.