Light as a Wave

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INTRODUCTION -The nature of light

Visit this site early in your study of this topic to get a sense of the history of the people of light as a wave.


   Light behaves

as a particle

would behave



as a wave

would behave

 By 1703, Isaac Newton (1642-1727) was firmly established as the preeminent natural philosopher (scientist) in England because of his work in mechanics. It was in that year that Newton, now in his sixtieth year, wrote a new book entitled Optics in which he espouses his belief that the nature of light is a collection of particles called corpuscles. These particles, traveling at sufficiently high speed, could: 1) travel in straight lines; and 2) reflect off flat surfaces in ways consistent with the laws of reflection. Refraction could be explained if the speed of light increased as it traveled into a denser transparent medium.

Consider a corpuscular model as described by Prof. Rubin

  In 1678, a Dutch scientist, Christiaan Huygens (1629-1695) suggested that light was a wave phenomenon. He believed that the phenomena exhibited by light at the time (rectilinear propagation, reflection, refraction) could be explained if light were a wave. He fashioned a model, known as Huygens’ Principle, which could explain how light could travel through space. Every point on a wave front can be considered a source-point for the next wave front. While Huygens ideas drew some interest in the eighteenth century, Newton’s corpuscles were generally accepted over Huygens’ wavelets.

Consider a wave model as described by Prof. Rubin.
See also Mr. Hwang's view of Huygens' principle

 The Conclusive Experiment

 Public opinion regarding the nature of light shifted in 1801 when a British physician, Thomas Young, performed his now-famous double-slit experiments, the results of which could be explained more easily and credibly by a wave theory.

Consider a glass plate painted flat black. If we take two razor blades positioned very close together and drag them across the plate, we can create two parallel slits very close together. What should happen if light shines on the slits and then proceeds to a distant screen. A corpuscular theory suggests that there should be two piles of light corpuscles collecting on the screen. In fact Young got a series of bright and dark bars. How can one explain this phenomenon? He argued that interference occurred between waves emerging from the two slits acting as independent light sources. He considered the path-length, the distance between each slit to points on the screen. When the path-length difference was an even number of half wavelengths, constructive interference occurred -- a bright bar was present. If the path-length difference was odd number of half wavelengths, dark bars appeared on the screen -- destructive interference.


nature of waves

A. Wave Jargon - Terms to Know

B. Interference by a double slit

C. Interference by a thin film

D. Diffraction

E. Polarization

F. The physics of color

This page was last modified by mgosselin on 10/08/2005

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