Lecture 11 - EM Waves (Ch. 24.5-24.7)

# Lecture 11 - EM Waves (Ch. 24.5-24.7) - Electro-magnetic...

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Electro-magnetic waves Ch 24

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The electromagnetic spectrum 4000 5000 6000 7000 Wavelength (Angstroms) 1 Angstrom = 10 -10 m
Frequency : Number of times per second that a crest passes a Fxed point. moves at speed c Longer wavelength => smaller frequency Will see later that higher frequency => higher energy photons

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Electromagnetic Waves Changing B fields create E fields Changing E fields create B fields Maxwell’s equations can be combined to show: 1. E and B fields obey wave equations: 2. Electromagnetic waves can be represented by plane waves, where E and B are perpendicular to each other and to the direction of propagation. 3. Electromagnetic waves propagate at speed c =
2. Electromagnetic waves are transverse waves. Direction of travel is: (Recall right-hand rule for cross-products) 1. The simplest solutions to the waves” with

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Electromagnetic waves are transverse waves. Direction of travel is: Direction of travel is: Propagation Propagation
Intensity o Intensity is Power per unit area

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Intensity of an EM Wave o The electric and magnetic fields of an EM wave both carry equal amounts of energy o The average intensity I over several cycles of a sinusoidal electromagnetic wave is
Example: Solar Power o Sunlight delivers I=1000 W/m 2 of intensity to the Earth’s surface. What is the total power that can be collected from a 100% efficient solar cell that covered a roof of 8m by 20m?

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o Sunlight delivers I=1000 W/m 2 of intensity to the Earth’s surface. What is the total power that can be collected from a 100% efficient solar cell that covered a roof of 8m by 20m? This is a lot of 50W light bulbs.
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## This note was uploaded on 09/08/2008 for the course PHYS 3B taught by Professor Wu during the Spring '08 term at UC Irvine.

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Lecture 11 - EM Waves (Ch. 24.5-24.7) - Electro-magnetic...

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