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Transcript 
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
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