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Isaac Newton 1643 - 1727 White light made of colors •Light behaves like small particles - corpuscles •Light travels in straight lines •Reflect off opaque surfaces •Penetrate transparent materials Newton Problems with Reflecting Telescopes * Longer focal length harder to make * Chromatic Aberration Newtonian Telescope • Light behaves like waves – 1600s Christian Huygens • Refraction & Reflection explained by wave theory of light • Problem – can’t see around corners By 1800 Light has component parts Light behaves as a particle William Herschel 1738 – 1822 Discovers Infra-red • 1801 • Johann Wilhelm Ritter discovers Ultraviolet Light – 1827 Thomas Young and Augustin Fresnel Measures wavelength Observes interference of waves http://micro.magnet.fsu.edu/primer/java/interference/doubleslit/ http://www.youtube.com/watch?v=GzbKb59my3U • 1820 Hans Christian Ørsted Discovers relationship between electricity & magnetism In 1802 Italian Gian Domenico Romagnosi had already announced this was ignored • 1845 Michael Faraday Predicts Fields around objects Electric Fields Magnetic Fields • Michael Faraday Light affected by a magnetic field • 1873 James Clerk Maxwell finds the mathematical relationship between electric fields and magnetic fields Electromagnetic Waves 1. Visible light is EM energy 2. There should be other EM frequencies • 1889 Heinrich Hertz Produces small electromagnetic waves that have properties of light Produces Radio Waves or “Hertzian waves” • 1895 Wilhelm Roentgen Discovers X - Rays By 1900 Light, Radio and X-rays are Electromagnetic Waves • 1930 Microwaves Explored – WW II pushes research – Commercial Research after war • 1914 Gamma Rays Included – Henri Becquerel “Becquerel’s Rays” – Marie & Pierre Curie Radioactivity discovers new elements Polonium & Radium – Paul Villard finds stronger rays emitted by radium – 1914 Ernest Rutherford measures wavelength Early 1900s We know “light” is a form of electromagnetic radiation There are many different “kinds” of light or electromagnetic radiation Think of Light as a stream of particles Each particle has a certain amount of energy Is Light a Wave or a Particle? Wave Particle Duality