23_emr_models - Lesson 23 Models of Electromagnetic...

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Lesson 23: Models of Electromagnetic Radiation Scientists spend a lot of time coming up with, refining, and sometimes disproving models of natural phenomena. Light is a great example of just how much competing models can divide the scientific community, but also allow us to eventually understand the universe much better. The models that are discussed here, and the people that came up with them, will be coming up in later lessons when we need to look at the details of their work. Historically, models of light were divided into two groups: Particle (or corpuscular ) model: light is made up of small particles of actual stuff. Wave model: light is made up of some kind of wave. Particle Model of Light The particle model of light was the one that Sir Isaac Newton believed in. Because Newton believed in it, his influence in the scientific community forced many people to follow a particle model of light even when other evidence seemed to show it could be wrong. Newton did have good reasons to believe that light was a particle. .. 1. Light travels in straight lines. If light is a particle then it will not be able to diffract after going through an opening or around an obstacle. Particles always move in straight lines, and light seems to move in straight lines. When you shine a bright light on a person you expect to see a shadow on the ground, not light bending around the person to fill in all the ground behind them with light. 2. Light can be reflected. Just like when you shoot a hockey puck against the boards and it bounces off, little particles of light could be doing the same thing. 3. Light can travel through a vacuum. In Newton's time, the only waves that anybody really knew much about were mechanical waves , which need a substance (a medium) to move through (e.g. sound travels through air). Since they also had a pretty good idea in Newton's time that the space between the Earth and the Sun was a vacuum, how could light reach earth if it was a wave? If light is a particle it would have no trouble moving through a vacuum. Wave Model of Light
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This note was uploaded on 12/02/2011 for the course PHYSICS 235 taught by Professor Staff during the Fall '08 term at Rutgers.

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23_emr_models - Lesson 23 Models of Electromagnetic...

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