What is Light? (THE ELECTROMAGNETIC SPECTRUM). ALL ELECTROMAGNETIC WAVES TRAVEL AT THE SPEED OF LIGHT. 300 000 000 m / s. c = 300 000 000 m/s. λ. The Electromagnetic Spectrum. WAVELENGTH. SHORT WAVELENGTH. LONG WAVELENGTH.
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What is Light? (THE ELECTROMAGNETIC SPECTRUM)
ALL ELECTROMAGNETIC WAVES TRAVEL AT THE SPEED OF LIGHT 300 000 000 m / s c = 300 000 000 m/s
λ The Electromagnetic Spectrum WAVELENGTH SHORT WAVELENGTH LONG WAVELENGTH OUR EYES CAN ONLY SEE A SMALL FRACTION IN THE MIDDLE OF THE WHOLE SPECTRUM Which colour has the longer wavelength, red light or violet light? Which colour has the greater frequency, red light or violet light?
Most “Light” is not visible • Infrared radio/light waves have a very long wavelength; their wavelength is longer than visible light. Infra-red can be detected by special infra-red film and cameras. • If the police or Mounties shine an infra-red light on you they will be able to take a picture of your heat radiation using infra-red film: you will not know that they have taken your photo. You have been warned!!! • Animals like the pit-viper have infra-red vision so that they can find their warm prey in the dark. You have been warned again!!!
Cool Visual Spectrum Facts • If our eyes were as sensitive as those of goldfish we'd see the infra-red beams that control our TVs and DVD players. • Goldfish can also see ultra-violet light (the other end of the visible colour spectrum) which is also invisible to humans. Journal of Fish and Biology, 1999, Vol. 54, (921-943)
Different animals see different colours (wavelengths) of light. • There are hidden sights to be seen in flower petals, fish scales, and butterfly wings that we will never see with our naked eyes!
FREQUENCY: THE FREQUENCY OF A WAVE IS THE NUMBER OF WAVES EMITTED PER SECOND Frequency, f, is measured in HERTZ Hz
Hence SPEED FREQUENCY and WAVELENGTH: The speed at which the crests move along, c, the frequency of the waves, f, and their wavelength, λ, are related by the formula: speed = frequency times wavelength c = f λ c = f x λ
The Electromagnetic Spectrum FREQUENCY INCREASING WAVELENGTH INCREASING ELECTROMAGNETIC RADIATION COMES IN BURST CALLED PHOTONS HIGH FREQUENCY RADIATIONS TEND TO BE PENETRATE DEEPER INTO SURFACES
Gamma Ray photon; wavelength 10-11 – 10-13 metres, i.e. about a million millionth of a metre APPLICATIONS: -sterilizing medical equipment in hospitals -pasteurizing certain foods to prolong shelf life -treatment of cancer -gauge the thickness of metal in steel mills -radiography – patient ingests radioactive source, whereabouts in the body is then located with a gamma camera
X Ray photon; wavelength 10-9 – 10-11 metres, i.e. about a billionth of a metre… about the size of an atom APPLICATIONS: -radiography -treatment of cancer cells -airport security checks -studying atomic and molecular structure ….. X-Ray crystallography
Ultra Violet light wavelength 10-7 – 10-8 metres, i.e. about a ten millionth of a metre… the size of a virus APPLICATIONS: -criminology…. some stains [e.g. blood] fluoresce under uv light -security marking -detection and destruction of bacteria -phototherapy treatment of skin complaints, e.g. psoriasis
0.4 μm 0.7 μm wavelength about 0.5 micrometres [μm] or half a millionth of a metre VISIBLE LIGHT Protazoa size
pinhead to cell wavelength about 1mm to 1μm INFRA RED APPLICATIONS: -night-time surveillance -medical: CO2 laser surgery & thermal imaging -weather forecasting -remote controls -heat seeking missiles
microwaves & radar Wavelength: a few centimetres APPLICATIONS: -radar inc. weather forecasting -cooking -telecommunications inc. mobile phones
TV & RADIO APPLICATIONS & WAVELENGTHS: Ultra High Frequency - UHF for TELEVISION …… about 10 cm Very High Frequency - VHF for FM RADIO ……. about 1 metre Short Wave – SW … AM Radio …… 10m & 50m bands Medium Wave – MW … AM Radio …… 200 to 600m Long Wave – LW … AM Radio …… 1000 to 2000m
Colours We See: So what are some major ways that we produce different colours?
Colour By Subtraction and Addition • Additive colour allows light wavelengths to get to your eyes the combination of these add up to specific colours. (ex. Stained glass) • Subtractive colour removes light waves by absorbtion. (ex. paintings)
Additive verses Subtractive colour theory
Colour • In both additive and subtractive colour theory it is the end result of specific wavelengths striking the back of the eye that results in colour perception
FOR YOUR INFORMATIONGo farther to see how reflection and absorbtion changes our environment. And why green plants are successful.
Albedo Value The albedo value gives a ratio of the amount of radiation or light reflected compared to the total amount of incident radiation or light.
Planetary Albedo is Effected by Atmospheric and Environmental Status
Albedo and the Ice Caps • Water and ice also reflect different amount of incident light. Satellites use the albedo factor of water compared to that of ice to examine the melt status of planetary ice caps.
Why are plants green? • Green is the colour with the highest absorption factor at the earth’s surface. • Plants are green for the simple reason that maximizing albedo mean absorbing the most energy. • Absorbing the most energy translates into successful living when it comes to plants as well as photosynthesizing cyanobactria!