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 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 –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 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