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Isaac Newton 1643 - 1727
•Light behaves like small particles - corpuscles
•Light travels in straight lines
•Reflect off opaque surfaces
•Penetrate transparent materials
White light made of colors
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
http://micro.magnet.fsu.edu/primer/java/interference/doubleslit/
http://www.youtube.com/watch?v=GzbKb59my3U
Measures wavelengthObserves interference of waves
• 1820 Hans Christian Ørsted
Discovers relationship between electricity & magnetismIn 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 lightProduces 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– Marie & Pierre Curie
– Paul Villard finds– 1914 Ernest Rutherford
“Becquerel’s Rays” Radioactivity
discovers new elements Polonium & Radium
stronger rays emitted by radium
measures wavelength
Early 1900sWe 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