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# Light

## by joverba on Oct 19, 2011

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## LightPresentation Transcript

• What is Light?
• Properties of Waves All electromagnetic waves travel at the same speed The speed of light: 300,000,000 m/s trough crest
• Wavelength (length/cycle) Wavelength (  ): the length of one complete cycle trough crest Properties of Waves All electromagnetic waves travel at the same speed The speed of light: 300,000,000 m/s
• Wavelength (length/cycle) Amplitude : 1/2 height between trough and crest Amplitude trough crest Properties of Waves All electromagnetic waves travel at the same speed The speed of light: 300,000,000 m/s
• Wave Speed = wavelength x frequency Wave Speed =  f (length/second) = (length/cycle) x (cycle/second)
• Light as a Wave Light waves are characterized by a wavelength  and a frequency f c = 300,000 km/s = 3  10 8 m/s l
• Electromagnetic Waves
• Light as a Wave Wavelengths of light are measured in units of nanometers (nm) or Å ngstr öm (Å) : 1 nm = 10 -9 m 1 Å = 10 -10 m = 0.1 nm Visible light has wavelengths between 4000 Å and 7000 Å (400 nm – 700 nm) .
• The Electromagnetic Spectrum Need satellites to observe Wavelength Frequency High flying air planes or satellites
• Wavelengths and Colors D i f f e r e n t colors of visible light correspond to different wavelengths.
• Visible Light (VIS) 700 to 400 nm Our eyes are sensitive to this region of the spectrum Red - Orange - Yellow - Green - Blue - Indigo - Violet
• Solar Radiation The Source for 99.9% of Earth’s Energy
• Solar Spectrum The sun emits radiation at all wavelengths Most of its energy is in the IR - VIS - UV portions of the spectrum ~50% of the energy is in the visible region ~40% in the near-IR ~10% in the UV Wavelength (m)
• Have the longest wavelengths and lowest frequencies of all the electromagnetic waves.
• A radio picks up radio waves through an antenna and converts it to sound waves.
• Each radio station in an area broadcasts at a different frequency. # on radio dial tells frequency. MRI (MAGNETIC RESONACE IMAGING)
• Uses radio waves with a magnet to create an image
• MICROWAVES
• Microwaves —have the shortest wavelengths and the highest frequency of the radio waves.
• Used in microwave ovens.
• Waves transfer energy to the water in the food causing them to vibrate which in turn transfers energy in the form of heat to the food.
• Used by cell phones and pagers.
• RADAR ( Ra dio D etection a nd R anging)
• Used to find the speed of an object by sending out radio waves and measuring the time it takes them to return.
• INFRARED RAYS
• Infrared = below red
• Shorter wavelength and higher frequency than microwaves.
• You can feel the longest ones as warmth on your skin
• Heat lamps give off infrared waves.
• Warm objects give off more heat energy than cool objects.
• Thermogram —a picture that shows regions of different temperatures in the body. Temperatures are calculated by the amount of infrared radiation given off. Therefore people give off infrared rays.
• VISIBLE LIGHT
• Shorter wavelength and higher frequency than infrared rays.
• Electromagnetic waves we can see.
• Longest wavelength= red light
• Shortest wavelength= violet (purple) light
• When light enters a new medium it bends (refracts). Each wavelength bends a different amount allowing white light to separate into it’s various colors ROYGBIV.
• ULTRAVIOLET RAYS
• Shorter wavelength and higher frequency than visible light
• Carry more energy than visible light
• Used to kill bacteria. (Sterilization of equipment)
• Causes your skin to produce vitamin D (good for teeth and bones)
• Too much can cause skin cancer.
• Use sun block to protect against (UV rays)
• X- RAYS
• Shorter wavelength and higher frequency than UV-rays
• Carry a great amount of energy
• Can penetrate most matter.
• Bones and teeth absorb x-rays. (The light part of an x-ray image indicates a place where the x-ray was absorbed)
• Too much exposure can cause cancer
• (lead vest at dentist protects organs from unnecessary exposure)
• Used by engineers to check for tiny cracks in structures.
• The rays pass through the cracks and the cracks appear dark on film.
• GAMMA RAYS
• Shorter wavelength and higher frequency than X-rays
• Carry the greatest amount of energy and penetrate the most.
• Used in radiation treatment to kill cancer cells.
• Can be very harmful if not used correctly.
• SUMMARY
• All electromagnetic waves travel at the same speed. (300,000,000 meters/second in a vacuum.
• They all have different wavelength and different frequencies.
• Long wavelength-  lowest frequency
• Short wavelength  highest frequency
• The higher the frequency the higher the energy.
• Light as Particle
• Light also behaves like a particle
• This particle is called a photon
• The energy of a photon is dependent on its frequency
• A photon is like a little packet (quantum) of electromagnetic energy.
• Where do photons come from?
• Photons come from atoms
• Atoms absorb and emit photons at certain specific frequencies.
• This is because the electrons can only be in certain orbitals.
• Atomic Emission e -
• This means…
• Atoms of an specific element absorb or emit only specific frequencies of electromagnetic energy.
• This is called the absorption or emission spectrum.
• Using this in astronomy
• Astronomers can use these spectra to determine the composition of stars and planets and other stellar objects.
• The Sun’s Emission Spectrum
• Wave particle duality
• SUMMARY
• Light can also behave light particles called photons.
• These photons come from the electrons in atoms.
• Because electrons can only be in specific orbitals, only specific frequencies are emitted or absorbed.
• These specific frequencies (spectrum) can be used to determine what elements are present.
• Spectroscopy
• Using wavelength/frequency to determine composition
• Can use light emitted
• emission
• Or light absorbed
• absorption
• Light and temperature
• Electromagnetic spectrum also tells temperature
• More heat = more energy
• More energy = higher frequency
• Higher frequency = More heat
• electromagnetic radiation emitted an object because of the object's temperature
• Temperature of Stars
• Gamma and x-ray emitters are hottest
• Blue stars are hotter
• Red stars are colder
• Kelvin
• Kelvin is the astronomer’s temperature scale
• Abbreviation : K
• K= ºC + 273
• So… 0K = -273ºC
• What’s colder than cold?
• Absolute zero!
• 0K
• Absolutely NO atomic motion
• None
• Zip
• Zilch
• No not even a little.
• Deep space is just a few degrees above absolute zero
• Summary
• Spectroscopy is using electromagnetic radiation to determine composition
• This can be used to determine the temperature and composition of stellar objects
• Absolute zero (0K) is no atomic motion
• Manipulating Light
• Manipulating, or working with, light is what astronomers do
• We have two main ways to manipulate light:
• Refraction
• Reflection
• Refraction
• Changing the direction of light as it passes through some medium
• For example:
• Straw in drink
• lenses
• Refraction
• Refracting Telescope
• Focus light through a series of lenses
• Like what Galileo used
• Reflection
• Can be done with more than just visible light!
• Reflecting Telescopes
• Focus light through a series of mirrors
• Invented by Isaac Newton
• Reflecting Telescopes
• Allow for larger telescopes
English astronomer William Herschel built this huge reflecting telescope in the late 1700s.
• Work like visible light reflector scopes
• Cassiopeia in visible light