Isaac Newton
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 Measures wavelength Observes interference of waves
1820 Hans Christian Ørsted –Discovers relationship between electricity & magnetism –In 1802 Italian Gian Domenico Romagnosi had already announced this was ignored
1845 Michael Faraday –Fields
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” Radioactivity –Marie & Pierre Curie discover 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