Lect23 - Physics 212 Lecture 23 Physics 212 Lecture 23...

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Physics 212 Lecture 23, Slide 1 Physics 212 Lecture 23
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Music Who is the Artist? A) Bob Wills and the Texas Playboys B) The Viper and His Famous Orchestra C) Big Sandy and the Fly-Rite Boys D) Pokey LaFarge and the South City Three E) Blind Boy Paxton Why? They were the headliners at the CU Folk and Roots Festival this past weekend. They were wonderful !! See who you missed at: http://www.folkandroots.org/site/2011-artists
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Physics 212 Lecture 23, Slide 3 Your Comments 05 “So, according to the Doppler Effect, the only thing I have to do to get X- Ray Vision is run away from whatever I want to see through? Also: would it work if said thing was running away from me? (Always looking for ways to minimize the work I have to do)” “Sometimes, you can't deny that physics is just awesome. Doppler effect seen from moving stars?? So cool!” We’ll do a Doppler shift example anyway (& discuss approximations) “This lecture was fun!” It certainly can be confusing.. We will try to make it clear !! “I don't understand what the equations mean with the (kz+-wt).” “super hard” “Can you explain the E and B electromagnetic waves graph in more detail? I'm still confused. ” “Seriously? You mispell "pointing" and then expect us to run at our iclickers so as to see the magical waves they emit? SMH”
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Physics 212 Lecture 23, Slide 4 Your Comments 05 “PLEASE READ MEEEEEEEEEEEEEEE. <----- Don't post this annoying part =D I set the equations of (energy density )*(Volume) = planck's constant *(c/lambda) . Solving for lambda I see that the wavelength decreases as Volume increases. Does that mean that EM waves loose their wavelength as the Universe expands?” YES! Photons left over from the Big Bang (starting out with the energy that binds electrons to protons = hydrogen atom) have lost a lot of energy as the universe expands (from t = 400,000 years to now) λ initial 100 nm = 10 -7 m, λ today 1 mm: the cosmic microwave background
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Physics 212 Lecture 23, Slide 5 Plane Waves from Last Time E and B are perpendicular and in phase Oscillate in time and space Direction of propagation given by E X B E 0 = cB 0 Argument of sin/cos gives direction of propagation
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Physics 212 Lecture 23, Slide 6 Understanding the speed and direction of the wave E x z t = 0 E x = E o sin(kz- ω t) What has happened to the waveform in this time interval? It has MOVED TO THE RIGHT by λ /4 f c speed λ π ω λ ω π λ = = = = 2 2 / 4 / t = π /2 ω E x z ) cos( ) sin( 2 kz kz - = - π
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Physics 212 Lecture 23, Slide 7 Checkpoint 1a “The value at t=0 is 0 for this function and it is positive in the x direction right after” “Since the sine wave is going up, its - the omega t” “The terms within the sin function show that the wave is moving in the +z direction and B is in the y plane so it's By.”
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Physics 212 Lecture 23, Slide 8 No – moving in the minus z direction No – has E y rather than E x Checkpoint 1a
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Physics 212 Lecture 23, Slide 9 Wavelength is equal to the speed of light divided by the frequency.
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