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     light light Presentation Transcript

    • Galileo Galilei (1564 – 1642) “Revealing great, unusual and remarkable spectacles, opening these to the consideration of every man, and especially of philosophers and astronomers….” SUNSPOTS
    • What is Light?
    • Properties of Waves All electromagnetic waves travel at the same speed The speed of light: 300,000,000 m/s crest trough
    • Properties of Waves All electromagnetic waves travel at the same speed The speed of light: 300,000,000 m/s Wavelength crest (length/cycle) trough Wavelength (λ): the length of one complete cycle
    • Properties of Waves All electromagnetic waves travel at the same speed The speed of light: 300,000,000 m/s Wavelength crest (length/cycle) Amplitude trough Amplitude: 1/2 height between trough and crest
    • Wave Speed = wavelength x frequency Wave Speed = λ f (length/second) = (length/cycle) x (cycle/second)
    • Light as a Wave l c = 300,000 km/s = 3×108 m/s Light waves are characterized by a wavelength λ and a frequency f
    • Electromagnetic Waves
    • Light as a Wave Wavelengths of light are measured in units of nanometers (nm) or Ångström (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 Wavelength Frequency Need satellites to observe High flying air planes or satellites
    • Wavelengths and Colors Different 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
    • Light as Particles • Light can also behave like a stream of particles, called photons • A photon has a specific energy E, • Energy is proportional to frequency and inversely proportional to wavelength E = h×f In other words, waves with shorter wavelengths (or higher frequency) have higher energy h = 6.626x10-34 J*s is the Planck constant. The energy of a photon does not depend on the intensity of the light!!!
    • 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)
    • RADIO WAVES    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 (Radio Detection and Ranging) • 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.