Lecture07

Lecture07 - 9/2/10 Light and Matter The Speed of Light is...

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9/2/10 1 ©2010 W.W. Norton & Company, Inc. Light and Matter Almost all knowledge of the Universe beyond Earth comes from light. Light can tell us about objects in space: temperature, composition, speeds, and more. ©2010 W.W. Norton & Company, Inc. The Speed of Light is Finite Light moves at 300,000 km/s in a vacuum. First measured by Rømer when observing Jupiter’s moons. Speed is slower in other materials, e.g., glass. ©2010 W.W. Norton & Company, Inc. Light is an Electromagnetic Wave Light is a wave of combined electricity and magnetism, called an electromagnetic wave. Changing electric and magnetic fields create a self-sustaining electromagnetic wave. ©2010 W.W. Norton & Company, Inc. Waves Wavelength ( λ ): length between crests. Amplitude : height Frequency ( f ): number of waves that pass by each second Period ( P ): Time to complete one cycle
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9/2/10 2 ©2010 W.W. Norton & Company, Inc. Wavelength, Frequency, and Speed A long wavelength means low frequency. A short wavelength means high frequency. The speed of light, c, is constant. ©2010 W.W. Norton & Company, Inc. Waves in What? Water waves, sound waves, and so on, travel in a medium (water, air, …) Electromagnetic waves need no medium Created by accelerating charged particles: ©2010 W.W. Norton & Company, Inc.
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Lecture07 - 9/2/10 Light and Matter The Speed of Light is...

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