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• Measures wavelength

• Observes interference of waves

http://micro.magnet.fsu.edu/primer/java/interference/doubleslit/

• 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 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