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Three models of light (2013)

Page history last edited by Joe Redish 4 years, 11 months ago

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Light and sound have much in common.  Both can be described in several different ways.  One of the most common models for thinking about them are to consider them as waves.  Sound is a pressure wave where molecular density alternates between high and low values while light is an electromagnetic wave where electric field alternates.  As waves, both can be described by the wave model where the wave has a characteristic wavelength, velocity and frequency.


These waves can also be described by the ray model, where a vector indicates the direction that the wave front is moving.  Waves will change direction and speed as they encounter an interface such as that between air and water and the ray model makes it easy to describe such changes.


Light has one more way it can be described and that is the particle model.  Quantum mechanics has shown that light can be described as particles with a given amount of energy.  These light packets of energy are called photons.  Actually, sound can also be considered as having discreet packets of energy called phonons, but this view of sound is less frequently used for large scale systems.


So which model should we use, the ray model, the wave model or the particle model?  We will use all three of them actually, depending on what we are trying to understand or describe.  They are equally relevant and one model does not preclude the conclusions that can be drawn from the others. 




Karen Carleton

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