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Lecture 15

AST 101 Lecture Notes - Lecture 15: Hitachi Maxell, Quantum Mechanics, Photon

Course Code
AST 101
Walter Freeman

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19th century electromagnetism:
Electric fields exert a force on electric charges
Magnetic fields exert a force on moving electric charges
Jaes Clerk Maxell suspeted that hagig eletri fields ake ageti fields i 86s
Changing electric field makes a magnetic field
o Which makes a magnetic field
Which makes an electric field further away
Electromagnetic waves move at speed of light, is it light?
We can only perceive a piece of the sound spectrum D
We can only perceive a tiny fraction of the light spectrum D
Radio waves microwaves infrared UV Xrays gamma (longer WL to shorter)
We see that specific wavelength band (IF-UV, rainbow) because it is the light that sun emits
humans have evolved to see the colors of the sun
These electromagnetic waves have the same properties as water, sound, and string waves
Wavelength distance from one crest to the next
Wave speed
Frequency number of wave crests passing a given point per second
Intensity (amplitude)
Light is always the same speed
Light traveling thru empty space always travels at the speed of light c
Quantum mechanics
Says that things in nature in both particles and waves simultaneously
Dual nature of light
Light comes in little chunks called photons still exhibit wave properties even though
they are discrete
Longer the wavelength the less energy carried per photon
o Radio enough energy to cause minate changes in atoms
o Microwaves enough energy to make molecules rotate
o Visible light energy to excite atoms
o UV energy to tear electrons off atoms
o X-ray enough energy to do this to many atoms and keep on going
o Gamma energy to excite an atomic nucleus
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