Electromagnetic Radiation (including visible light)

Transcription

1 An expert is a man who has made all the mistakes, which can be made in a narrow field. Neils Bohr Electromagnetic Radiation (including visible light) Behaves like a particle. light particles are called photons. Also Behaves like a wave. All EMR moves at the speed of light: (c=3x10 8 m/s) Like all waves, electromagnetic waves carry energy. Vibrating electric & magnetic fields regenerate each other and make up an electromagnetic wave. 2 Types of Wave: Mechanical Electromagnetic Wave Wave Any wave that requires a medium to travel. For example, water waves require water! Sound Wave Water Wave Slinky Wave A wave that does not require a medium. A disturbances in electric and magnetic fields Examples: Light Radio Waves X-Rays UV Rays Spectrum of Visible Light Herschel s Experiment Herschel s Experiment Discovered Invisible Light In 1800, Herschel places his control thermometer just outside the red end of the spectrum Result: The outside thermometer registered the highest temperature 1

2 Conducting Hershel s Experiment Wavelength and Frequency If both these waves are traveling at the same speed, which one has the higher frequency? Wavelength and Frequency Since all light travels at the speed of light, High f means small wavelength Large wavelength means low frequency. Low Energy Low Frequencies Large Wavelengths High Energy High Frequencies Small Wavelengths Low Energy Low Frequencies Large Wavelengths High Energy High Frequencies Small Wavelengths 2

3 Radio Waves Low Energy Low Frequency Large Wavelength Radio Waves Radio waves have useful properties: 1) Travel far through the atmosphere 2) Easily generated by setting up currents in metal antennas 3) They bounce off the ionosphere, AM = Amplitude modulation and thus travel long distances FM = Frequency modulation around Earth. Microwave Microwaves : Microwave Ovens Gas clouds collapsing into stars Cell Phones Microwave Telescopes Food (heated) Cell phones Radar systems) Microwaves are not obstructed by clouds, haze or any other particle smaller than the microwave wavelengths (~ 1 cm). They can be used to image Earth s surface through the clouds that cover ~50% the globe. Microwave photo of the Amazon Cosmic microwave background Infrared (Near and Thermal) Sun and stars (Near) TV Remote Controls Food Warming Lights (Thermal) Everything at room temp or above Infrared Cameras TVs, VCRs, Your skin Infrared Radiation Wavelength: 1 um 1000 um We emit IR light. In fact all the objects around us emit IR radiation. Hotter objects emit more IR radiation, which we are warmed by, and which we sense with our skin. IR photo of a man IR photo of the dust in the Solar System 3

4 The sun and other astronomical objects Laser pointers Light bulbs Cameras (film or digital) Human eyes Plants (red light) Telescopes Visible Visible Light We see the very part of the electromagnetic that the Sun emits. That is we have detectors that are sensitive the radiation that illuminates our world. White light is made up of light from all different colors Ultraviolet Tanning booths (A) The sun (A) Black light bulbs (B) UV lamps Space based UV detectors UV Cameras Flying insects (flies) Ultraviolet Light Ultraviolet light has just the right energy to break molecular bonds apart. For this reason it is detrimental to life. The Earth has a natural shield to Solar UV light in the form of an ozone layer (80 km above the surface). Some birds & bees can see UV as well as visible light. 10% of sunlight is in the UV X-rays X-rays Astronomical objects X-ray machines CAT scan machines Older televisions Radioactive minerals Airport luggage scanners Space based X-ray detectors X-ray film CCD detectors X-rays were discovered 1895 by Wilhelm Conrad Roentgen (a German scientist) by accident. A week later he took this x-ray of his wife. 4

5 Chandra X-ray Observatory Gamma Ray Chandra X-ray Observatory Chandra is designed to observe X-rays from high energy regions of the universe, such as the remnants of exploded stars. The most sophisticated observatory built to date. Deployed by the Space Shuttle Columbia on July 23, 1999, Radioactive materials Exploding nuclear weapons Solar flares Gamma detectors and astronomical satellites Medical imaging detectors Sources of gamma-ray Emission Black holes Active Galaxies Pulsars Supernovae Unidentified Sources Gamma Rays Wavelength: m Gamma Rays are the most energetic of all electromagnetic waves. These EM waves are therefore emitted in the hottest events. Gamma Ray Bursts: Can release more energy in 10 seconds, then released by the Sun in 10 billion yrs. Their source is unknown. Exploring the EMS with NASA Missions Radio Infrared Visible UV X-ray Gamma ray Energy (ev) MAP SWAS GALEX Chandra RXTE CHIPS ASTRO-E2 Swift HETE-2 Con-X INTEGRAL XMM-Newton GLAST 5

6 Reflections of Radiated Energy (Jones 1997) Reflections of Radiated Energy (Longley 2001) TM Bands TM Bands 1(B) 2(G) 3(R) = BGR (visible) TM Band 4, 3, and 2 (NIR G R = RGB) Healthy Vegetation Urban Areas Moist Wetlands Water And the universe for that matter! 6