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lecture02

# lecture02 - Astronomy Picture of the Day...

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Astronomy Picture of the Day http://antwrp.gsfc.nasa.gov/apod/astropix.html The zodiacal light

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Light and Radiation Light is a wave phenomenon To understand how light behaves, we need to understand the general properties of waves
Waves Waves are periodic disturbances propagating through some medium. Some examples: Waves on the surface of a body of water Sound waves propagating through air Waves propagating along a vibrating string Light waves Important point: the wave disturbance travels through the medium: the medium itself does not travel with the wave

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Properties of waves Amplitude : the height of a wave crest A
Properties of waves Wavelength : the distance between two successive wave crests (or two successive troughs) Wavelength is denoted by the Greek letter λ (lambda) λ λ

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Properties of waves Frequency : the number of wave crests passing a fixed point each second Frequency is denoted by the Greek letter ν (nu) Units for frequency: 1 Hertz (Hz)= 1 wave cycle per second Count how many wave crests pass a fixed marker in 1 sec
A note about units One Hertz means one event (of some kind) per second In other words: the unit Hz is the same as 1/second

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Properties of waves For high frequencies, use units of kilohertz (kHz): 1000 cycles per second megahertz (MHz): 1 million cycles per second gigahertz (GHz): 1 billion cycles per second Count how many wave crests pass a fixed marker in 1 sec
Properties of waves Speed or velocity : how fast a wave crest is traveling Wave speed measured in meters per second velocity v

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Example: 2 waves moving with the same speed Shorter wavelength, higher frequency Longer wavelength, lower frequency
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