| Themes > Science > Physics > Optics > What is Light? > The Electromagnetic Spectrum | ||||||||||||||||||||||||||||
The table below describes the different radiations of the Electromagnetic Spectrum. I must emphasise that these radiations are all the same except for the difference in wavelength. They have different names because of historical reasons and the way they are generated. The boundaries between the different radiations are all artificial. As you progress from Radio Waves through to Gamma Rays, the wavelength gets shorter (so they become more penetrating), the frequency gets higher (so the oscillation needed to produce them gets faster), and the energy gets higher (so it takes more energy to produce Gamma Rays than it does to produce Radio Waves).
All matter produces radiation. Radio Waves are produced when free electrons are forced to move in a magnetic field, or when electrons change their spin in a molecule. They are used for communication and to study low energy motions in atoms. All electrical goods generate Radio Waves. Radio Waves from space can be used to study cool interstellar gases. Radio Waves cannot be detected by humans. Infra Red radiation is produced by the vibrations of molecules. Human skin feels this radiation as heat. Microwave ovens work by using Infra Red radiation of the correct frequency to make the water molecule vibrate faster. A faster vibrating molecule is a hotter molecule. Only the food which contains water is affected. The plate which is a dry mineral is unaffected. Infra Red is used as an analytical tool for molecules in Chemistry. Cool, proto-stars are studied with Infra Red detectors. Visible and Ultra Violet Light is produced by chemical reactions and ionisations of outer electrons in atoms and molecules. There are many chemical reactions that are instigated by this radiation: the chemical retinal in animal eyes, chlorophyll in plants, silver chloride in photography, the chemical melanin in human skin, silicon converts light to electricity. Light is the most familiar electromagnetic radiation because the Earth's atmosphere is transparent to it. Light (and a little of the Infra Red and Ultra Violet on either side of it) can pass through the atmosphere. Living organisms have evolved to use these waves. Visible Light is simply the part of the electromagnetic spectrum that reacts with the chemicals in our eyes. Bees can see more Ultra Violet than we can. Snakes can detect Infra Red. X-Rays are produced by fast electrons stopping suddenly, or by ionisation of the inner electrons of an atom. They are produced by high energy processes in space: gases being sucked in to a black hole and becoming compressed; exploding stars. They are used in medicine to look through flesh. In Physics the waves are small enough to pass between atoms and molecules so they can be used to determine molecular structures. Gamma Rays are produced by very high energy processes, usually involved with the nucleus of atoms. Radioactivity and exploding stars produce Gamma Rays. They are very dangerous because if they strike atoms and molecules they will do lots of damage. If the molecules are the long and complex molecules of life, death and mutation could occur. |
||||||||||||||||||||||||||||
|
|