L06 - Chapter 6: Electromagnetic Radiation – Motivation....

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Unformatted text preview: Chapter 6: Electromagnetic Radiation – Motivation. Models • On Earth, we live in an ocean of energy transported in the form of electromagnetic radiation 6.1,2 Ex : a) The sunlight transports electromagnetic energy, b) the cosmos bombards us with various forms of radiation, c) different phenomena on earth result in emission of electromagnetic radiation such as radio, infrared, visible light, ultraviolet, X-ray, etc. • In the context of our discussion about energy, we are especially interested in the solar radiation (related both to its potential as an unconventional source of energy, d as a element in the global worming) as well as in the radiation emitted in and as a element in the global worming) as well as in the radiation emitted in nuclear reactions What is electromagnetic radiation ? • For practical purposes, we currently employ two complementary models for light: 1. one that considers that it has a wave-like nature and 2. one that considers that it has a particle-like (corpuscular) nature • We need two models since in some instances light behaves as a wave and in others as particles Models for Radiation – Waves What is a wave ? 6.2 Ex : Waves are omnipresent in nature: a) the ripples transmitted on the water surface are transversal waves transmitting the oscillation of water, b) sound is a longitudinal wave 1. Vibrations are localized in space 2. Waves are propagated vibrations forming a succession of spatially distributed crests and troughs transversal or longitudinal crest trough How do we characterize a wave ? 1. Amplitude A : Maximum of oscillation 2. Frequency f : the number of complete waves (crest + trough) passing through a location per unit of time 3. Period T : the time for one complete wave to pass a location 4. Wavelength λ : The distance between two successive crests 5. Speed v : the speed of traveling one wavelength v f T λ λ = = λ A A v v Models for Radiation – the Wave-like Model 6.2 • According to the wave-like model, light is a combination of intertwined electric and magnetic fields oscillating perpendicular on each other, propagating in space as a wave with a speed in empty space 8 300,000,000 m s 3 10 m s c = = × c Ex : The wavelength of a red color light beam is 650 × 10 –9 m = 650 nm (10 –9 m is called • The wave-like nature seems to be confirmed by the fact that light behaves like a wave: it bounces off mirrors ( reflection ), it is bent by transparent interfaces between different optical media ( refraction ), it interacts with obstacles with sizes comparable with its wavelength ( diffraction ), it is refracted differently depending on its wavelength ( dispersion ), it transports energy proportional to the square of its amplitude, etc....
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This note was uploaded on 03/19/2012 for the course PHYSICS phy 121 taught by Professor Mario during the Fall '11 term at Miami University.

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L06 - Chapter 6: Electromagnetic Radiation – Motivation....

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