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Light

Light. Early Concepts. Ancient Greece Thought that light consisted of tiny particles. When they entered the eye, they created the sensation of vision. Socrates and Plato Thought that vision was streamers or filaments that came from the eyes.

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Light

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  1. Light

  2. Early Concepts • Ancient Greece • Thought that light consisted of tiny particles. • When they entered the eye, they created the sensation of vision. • Socrates and Plato • Thought that vision was streamers or filaments that came from the eyes. • You saw what the filaments came into contact with.

  3. Early Concepts • Empedocles • Thought that light traveled in waves. • Huygens (contemporary to Newton) also argued that light was a wave. • Basic question: Is it a particle or a wave?

  4. Particle vs. Wave • Particle Theory: • Supported by fact that light does not seem to spread out as waves do. • Wave Theory: • Huygens showed that in some cases light does spread out. • Became the accepted theory in 19th century.

  5. Einstein • Said that light consists of Photons • Massless bundles of concentrated electromagnetic energy. • Scientists now believe that light has a dual nature • It is both a wave and a particle. • We will only discuss the wave nature.

  6. Know your Alien Species <Wookie Jawa> <Bith Ewok>

  7. Speed of Light • It was originally not known whether light travels instantly or has a finite speed. • Many attempts to measure the speed failed.

  8. Roemer and Huygens • Roemer noted a discrepancy in the period of Io around Jupiter. • Period varied as Earth moved toward or away from Jupiter. • Huygens interpreted this as the light taking longer to reach Earth. • First evidence that light has a finite speed.

  9. Michelson • Experimented to determine the speed of light. • Used a spinning octagonal mirror. • If spun at just the right speed, he could see reflection from a light source. • Found that the speed of light is 2.99920 x 10^8 m/s. • We round this to 3.00 x 10^8 m/s. • This speed is a constant in a vacuum.

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