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Electromagnetic Spectrum – Main Features
All electromagnetic waves:
– travel at the speed of light: 3 × 108 m/s
– do not need a medium to travel through i.e. can travel through a vacuum
– can transfer energy
– are produced by particles oscillating or losing energy in some way
– are transverse waves
Invisible components of electromagnetic spectrum
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Component
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Source
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Detectors
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Properties
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Uses
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Gamma-rays
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Cobalt-60
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Photographic plate; GM-tube; Cloud chamber
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Very penetrating; Very dangerous
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Treatment of cancer; Gamma rays (image inside the body); finds flaws in metals; sterilises bandages, prolongs shelf-life of food (e.g. ice-cream)
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X-rays
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X-ray tubes
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Photographic plate; Fluorescent screen
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Very penetrating; Very dangerous
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Treatment of skin disorders; X-ray radiography; study of crystal structures; inspections of welds in steel joints or pipes
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Ultraviolet (U.V.)light
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Sun; sparks and arcs; mercury lamps; UV lamps
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Photo film; Photo cells; Fluorescent chemicals
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Absorbed by glass; Causes sunburn; damages and kills living cells
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Detect forgeries of signatures; Fluorescent tubes; Sterilisation; Sunbeds
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Infra-red (I.R.) light
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Sun; Warm and hot onjects (fires or people)
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Special photo film; LDR (Light depenendent resistor); Photodiode
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Causes heating when absorbed
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Radiators (Keeps occupants of room warm in winter); Cooking food; Finding burried warm bodies; IR satellite photos reveal diseased crops; Televesion controllers; Intruder alarms
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Microwaves
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Microwave communication dish
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Microwave-receiving aerials
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Absorbed by water and fats in food and people, hence is dangerous
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Microwave communication links (Radio and televesion); Microwave cooking, Radar communication
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Radio
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Radio transmitter
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Metal aerials; Tuned circuits
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Induces alternating currents in metal aerials
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Radio; TV and satellite communi- cations
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