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The Electromagnetic Spectrum. April 3, 20007. So far we have talked about Mechanical Waves…… but there are some waves that don’t need a medium to travel through…. We call these Electromagnetic waves (such as light) that travel throughout “matter-less” space. Visible. Microwaves. X-Ray.
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The Electromagnetic Spectrum April 3, 20007
So far we have talked about Mechanical Waves…… but there are some waves that don’t need a medium to travel through… We call theseElectromagnetic waves (such as light) that travel throughout “matter-less” space. Visible Microwaves X-Ray Radio Infrared Ultraviolet Gamma Larger Waves Smaller Waves
Transverse wave Light vs. Sound • Longitudinal wave • Does not require a medium • Requires a medium • Frequency tells you the pitch • Frequency tells you the color • Amplitude tells you the brightness • Amplitude tells you the loudness (decibels)
Speed of light 300,000 km/s (fast!) **As far as we know, NOTHING travels faster than the speed of light!! • Very fast compared to the speed of sound (.340 km/s)
Electromagnetic spectrum • Spectrum: the full range, in this case, the full range of light waves that can be given off by excited electrons. • Arranges light waves based on their wavelength and frequency Long wavelength = Low frequency Short wavelength = High frequency
Electromagnetic specturm • ALL electromagnetic waves travel at the same SPEED
Types of Electromagnetic waves 1. RADIO WAVES Lowest frequency and longest wavelength; used for communication.
Radiowaves • Very LONG wavelengths Just FYI!! • Radio and TV waves are regulated by the FCC (Federal Communications Commission) to reduce interference • AM Radio waves have a longer wavelength • (lower frequency) • FM Radio waves have a shorter wavelength • (higher frequency)
Microwaves A higher energy radio wave; used for cooking food
Microwaves Just FYI!! • Water and fat absorb energy carried by microwaves • When these molecules move around faster they get hotter and give off heat • Microwaves are absorbed by molecules up to 2 cm below the surface (this is why food is sometimes cold in the middle! YUK!)
Microwaves Just FYI!! • Used in radar because it penetrates rain and fog • Used by Cell phones • Does not occur naturally and is made by various forms of communication technology • SETI = Search for extraterrestrial Intelligence uses this frequency to search, because it is not made naturally
2. INFRARED WAVES Can’t be seen, but can be felt as heat. Everything gives off infrared radiation; it depends on the thermal energy
Infrared waves • Examples of Infrared waves: • TV's remote control • Fire • Radiators • Infrared film to photograph a house to reveal areas in the structure that are leaking and wasting heat • Infrared light is even used to heat food sometimes - special lamps that emit thermal infrared waves are often used in fast food restaurants! Just FYI!!
Primary source of Infrared Radiation is heat • or thermal radiation • Any object that has a temp. radiates in the infrared, even ice cubes Ex. Charcoal is not burning but will emit heat Just FYI!!
Infrared waves • How Infrared radiation is used: • Snakes in the ‘viper’ family have sensory “pits” that detect I.R., so they can detect warm-blooded prey • Infrared pictures can be taken using special cameras and film that detects differences in temperature • Once the pictures are taken, they assign different brightness or false colors to them to provide a picture our eyes can interpret Just FYI!!
3. VISIBLE LIGHT Part of the spectrum you CAN see. R O YGB I V The color of visible light depends on its frequency
4. Ultraviolet Light (UV) Present in sunlight and have enough energy to kill living cells
Ultraviolet Light • UV Light is used: • In Tanning beds • To sterilize surgical equipment • In Food processing • Invisible to the human eye • Some insects, like bumblebees, can see them Just FYI!!
Ultraviolet Light • Ozone absorbs highest energy UV light • UV Light can cause sunburns and eventually malignant melanomas
5. X-Rays • Enough energy to pass through most materials (skin) • Lead is one material that X –Rays cannot pass through
X-rays • X-rays were first observed and documented in 1895 by Wilhelm Conrad Roentgen, a German scientist • He found them quite by accident when experimenting with vacuum tubes. • Also can be created by a machine like those for medical x-rays Just FYI!!
Just FYI!! X-rays • Originate in nature deep in space in the hot nebulae of stars • The Earth's atmosphere is thick enough that virtually no X-rays are able to penetrate from outer space all the way to the Earth's surface
Just FYI!! • bones and teeth are dense and absorb more X-rays then your skin does • silhouettes of your bones or teeth are left on the X-ray film while your skin appears transparent • When X-ray light shines on us, it goes through our skin, but allows shadows of our bones to be projected onto and captured by film • Metal absorbs even more X-rays - can you see the filling in the image of the tooth
6. Gamma Rays Has the Highest energy of all of the electromagnetic waves Emitted by radioactive materials Used to treat cancer, Can go through concrete!
Gamma-rays • Smallest wavelengths and possess more energy than any other wave in the electromagnetic spectrum • Produced by the hottest regions of the universe • They are produced by: • violent events as supernova explosions or the destruction of atoms • The decay of radioactive material in space • Neutron stars and pulsars, and black holes • radioactive atoms and nuclear explosions Just FYI!!
Medical Uses: • Radioactive Tracers (put into a patients body and followed as it goes through) • A patient with lung problems can breathe in Xenon-133, a gas that emits gamma rays • A special camera is used to take pictures • The patient isn’t injured by the radiation because they quickly breathe out all the gas • Radiotherapy • Treatment of cancer Just FYI!!
