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The
Electromagnetic Spectrum: the family of
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This is a continuous band of electromagnetic radiation. It is not made up of particles of matter - rather of photons (not met until A level but these are little quanta (or packets) of energy)). Electromagnetic radiation is composed of rays of pure energy. All electromagnetic rays have similarities in that they all travel at the same speed in a vacuum - 3.0 x 108 m/s and are all made up of photons. Electromagnetic waves differ in their wavelength, frequency, energy and method of production, but their speed in a vaccuum is always the same. The parts of it are arranged in the table below in order of decreasing photon energy, decreasing frequency or increasing wavelength. Each part is named according to its origin and frequency/wavelength range. Light energy is the most familiar part of the spectrum and it is often referred to as the 'family of light'. Some parts of the e.m. spectrum can be directly detected by humans, others cannot. From memory you should be able to list the parts in order of energy (relate how that relates to frequency and wavelength) and know how they are produced, detected and their dangers and uses - a rough idea of their approximate wavelength is also useful! The range of values for wavelength is so vast that you need to know your S.I. prefixes to do calculations using the wave equation relating to the EM Spectrum. |
Electromagnetic Energy |
Source of radiation |
Detectors |
Typical Wavelength |
Uses
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Dangers |
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Radioactive nuclei |
Geiger-Müller tube |
10-12 m |
Radiotherapy Diagnostic work with a gamma camera Pipe leakage |
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X-ray tubes - produced when high energy electrons hit a metal target. Also given out from black holes and very bright stars |
Photographic film |
10-10 m (size of an atom) |
Medical
scanning for broken bones and tumours in tissue
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cancer and mutations deep in the body |
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Ultra Violet (UV)
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Very hot objects, sun, sparks, mercury lamps. |
Photographic film, skin (it causes sun tans and skin cancer -see ozone layer depletion), makes fluorescent things glow with visible light. |
10-8 m |
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Visible
Light
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Very
hot objects - like the Sun or stars, hot metals
(filament lamp), fluorescent objects, and visible lasers, LEDs.
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Eyes,
photographic film, an LDR.
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5 x 10-7 m (Red end is about 700nm - Blue end about 400nm) |
One of our main forms of one to one communication! Warning of dangers and location of food etc. Writing, painting etc. |
Very bright light can damage the retina |
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Infra Red (IR) |
Warm or Hot objects, sun, IR lasers |
Skin, a blackened thermometer, a thermistor. |
10-5 m |
To keep us warm To cook food Remote control devices for TV etc. |
High intensity can burn the skin and retina |
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Microwaves |
Short wave radio transmitters (cell phone communications) and microwave ovens (these contain a magnetron - a high-powered vacuum tube that generates coherent microwaves). . |
Aerial with a short wave radio set, or a satellite dish. Water filled objects (such as food) get very hot |
cm |
High intensity and/or energy can cause heating effects within tissue - whether other biological effects take place is debatable - some scientist think it may cause tumour growth - but this is not by the route recognized (it is none ionizing) | |
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Radio and TV transmitters |
Aerial with a TV set or a radio set. (they CANNOT be heard!!!!!) |
km |
Communication
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None known unless intensity is abnormally high |
Here is a link to PowerPoints on the EM Spectrum
Also see the following site - it has been written by another UK Physics Teacher and has lots of additional info: