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LSN 01-09 Last Revised: 24 Aug 10

FORCES – Energy - Light. LSN 01-09 Last Revised: 24 Aug 10. Agenda . Review light Review processes of light. Electromagnetic Spectrum. High Energy. Low Energy. Small Wavelengths. Large Wavelengths. Gamma Rays. Ultra Violet. Visible Light. Infrared.

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LSN 01-09 Last Revised: 24 Aug 10

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  1. FORCES – Energy - Light LSN 01-09 Last Revised: 24 Aug 10

  2. Agenda • Review light • Review processes of light

  3. Electromagnetic Spectrum High Energy Low Energy Small Wavelengths Large Wavelengths Gamma Rays Ultra Violet Visible Light Infrared Radio Waves X-Rays Micro Waves Communication Heating Lighting & Human Vision Technological Uses Communication & Cooking Medical - Arranges different types of radiation from small wavelength (high energy) to long wavelength (low energy)

  4. 93 million miles Earth Sun Nearest star to earth Earth Alpha Centauri Speed of Light - In a vacuum light moves 300,000,000 meter/second (3 x 108 m/s) or 670,444,952 miles per hour -- Light moves a little slower in fluids (air, water, etc) Sun light takes 8 minutes to reach the earth - In one year light moves 5,877,120,445,000 miles (5.88 trillion miles) This is a light year! 4 Light Years

  5. 3 Types of Spectra Absorption Spectrum: - Light passes through a gas cloud …. -- photons (light particles) at specific wavelength (color) excite atoms (jumps to higher energy level) -- specific wavelengths (colors) absorbed -- depends on what chemical elements are in cloud (like a fingerprint for a gas) - Continuous except for the colors that were absorbed by the gas Blackbody: - Idealized object that absorbs & emits all forms of radiation - Example: a star Figure from Universe by Freedman and Kaufmann https://www.cfa.harvard.edu/~jbattat/a35/cont_abs_em.html • Emission Spectrum: -Anything that absorbs must also emit • Gas cloud emits wavelengths (colors) it absorbed. -- Each absorbed photon will return to its unexcited ("ground") state • Will see emission lines if you view cloud without the blackbody in background Continuous Spectrum: 1. Continuous band of all colors Note: Emission spectrum + Absorption spectrum = Continuous spectrum

  6. Spectra of Different Types of Light Bulbs

  7. Absorption & Emission Spectra Emission Spectrum of Hydrogen Absorption Spectrum of the Sun Emission Spectrum of Helium Emission Spectrum of Nitrogen Emission Spectrum of Carbon Emission Spectrum of Sodium Emission Spectrum of Oxygen Emission Spectrum of Neon Emission Spectrum of Aluminum Emission Spectrum of Magnesium Emission Spectrum of Silicon

  8. Absorption Spectra Emission Spectrum of Sulfur Absorption Spectrum of the Sun Emission Spectrum of Argon Emission Spectrum of Potassium Emission Spectrum of Calcium Emission Spectrum of Iron Emission Spectrum of Krypton Emission Spectrum of Strontium Emission Spectrum of Xeon Emission Spectrum of Barium Emission Spectrum of Mercury Source: http://astro.u-strasbg.fr/~koppen/discharge/

  9. Refraction • “bending” of light ray as the ray moves from a less dense fluid to into a fluid of different density Less dense fluid Denser fluid  In  Out • Scattering • light beam redirected in all directions • shorter wavelengths (blue light) greater the scattering • Absorption • when a material decreases the intensity of the light beam ● Particle (air molecule or dust) • Reflection • “bouncing” off smooth surface • angle beam strikes the surface = angle beam leaves the surface Properties of Light

  10. Albedo Albedo = percent of solar energy reflected by a planet or object - high albedo = more energy reflected & less energy absorbed Albedo Albedo Earth = 37% Forest = 5-10% Moon = 12% Desert sand = 25 - 30% Average Cloud = 50-55% Ploughed Field = 14-17% Water = 8% Concrete= 14-17% Snow - new = 80 – 90% Snow - old = 45 – 70% Blacktop Road = 5-10%

  11. Radiative Transfer For ESS-Accelerated • Stefan – Boltzmann Law: • Relates energy radiated and temperature • E = T4 E = Irradiance (watts/m2)  = Stefan-Boltzmann Constant = 5.67 x10-8 Watts/m2 K4 T= temperature (K) • Wien Displacement Law: • Determines wavelength of peak radiation • m = (2897 m K)/ T m = peak wavelength T= temperature (K) Power per area mwavelength

  12. Radiative Transfer For ESS-Accelerated • Example: • What is the irradiance & peak wavelength of radiation given off by the human body (T = 37 C = 310 K)? • m = (2897 m K) / (310 K) E = (5.67 x 10-8Watts/m2 K4) (310K)4 = 9.34 m = 524 watts/m2 • Activity: Determine the irradiance & peak wavelength of ….. • Group 1: Sun T = 6000 K • Group 2: Earth T = 288 K • Group 3: Sirius T = 10,000K mE 0.58 m 7.35 x 107 watts/m2 10.1 m 390 watts/m2 0.29 m 5.67 x 108 watts/m2

  13. Questions ??

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