PHY 113 Lecture Notes - Lecture 17: Christiaan Huygens, James Clerk Maxwell, Geometrical Optics

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11 Jun 2018

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Wave Characteristics
It is light stimulates the eye, and it is this stimulation that allows people to see. What is the
nature of light? Fifth century BC philosophers speculated that light was made up of streamers
emitted by the eye making contact with an object. Other early Greek philosophers believed
that light travelled to the eye as tiny particles, while still others thought that light travels as
The nature of light was a difficult question to answer. By the 17th century, most scientists
believed that light was a wave. The problem with that theory, however, is that waves were
thought to require a medium through which to travel-air, water, and so forth. How, then, did
light travel through the vacuum of space? Dutch scientist Christiaan Huygens postulated the
existence of the ether, a hypothetical substance that permeated the entire universe and made it
possible for light to travel. Other scientists, most notably Isaac Newton, maintained that light
had to be a particle, but could not explain some of light’s wave-like properties.
In the 1860’s, Scottish physicist James Clerk Maxwell unified the existing theories about
electricity and magnetism. He found that electromagnetic waves traveled at speeds near or
equal to that of light. This strongly suggested that light, too, was an electromagnetic wave.
He was later proved to be correct.
In the late 19th century, Albert Einstein discovered that light could affect the movement of
electrons, which implied that light had a particulate nature. Einstein felt that it was not
necessary to conceive of light as wave or particle, only that it could behave as one or the
other depending on the circumstances.
Optics is the study of light and geometrical optics is the study of light as it applies to the path
that light travels. Geometrical optics is not concerned about the nature of light; it is
concerned only about the path that light follows. Light travels in straight paths, and this
accounts for shadows and images. Reflection and refraction also describe the paths that light
The study of wave motion will begin in this unit. The terminology used when talking about
waves as well as the characteristics of waves, will be described. Then, the study of
geometrical optics which includes:
-reflection of light from both plane mirrors and curved mirrors
-refraction of light, including concave and convex lenses.
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