r v = Q enclosed r r E d r l = $ d% B dt r B d r i through dt Where does the word "laser" come from?

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1 Where does the word "laser" ome from? A: The name of the physiist who invented it. B: The name of the dog of the physiist who invented it C: "Light Amplifiation by Stimulated mission of Radiation" D: It's a mix of "light" and "phaser" : It was just made up beause it sounded ool 1 CAPA #14 Tonight. Set #15 in bins - short! Reading: If you haven t already -> 33.9, 34.7, 8 There is a new (and final!) online partiipation available - don t forget about it! Last: Maxwell's equations, light, and M radiation Today: More of Maxwell and M radiation Next: Waves, LC iruits and resonane. (Prof. Gurarie) 2 r "" da v = Q enlosed /# 0 r "" B da v = 0 r d r l = $ d% B " dt r B d r d% " l = µ 0 i through + µ 0 # 0 dt Maxwell s equations. The axioms of eletromagnetism. They are one of the major triumphs of modern siene! 3 1

2 Visible Light: xample: Yellow light Frequeny = 514 Hz λ = nm (yellow) 4 Traveling wave λ Wavelength λ /T = f λ = x (position) 5 Visible Light: λ= 400 nm (violet) 700 nm (red) xample: f λ = λ = 550 nm (yellow) f = /λ = 3x10 8 /550x10-9 = 5x10 14 Hz 6 2

3 Television transmissions are in the radio range. λ = 1-5 meters f =/λ ~ 10 8 Hz = 100 MHz On Television, different hannels have different frequenies and thus different wavelengths. When you set the hannel knob, you amplify just that frequeny range. 7 A radio wave of wavelength 2 meters passes by a person with a radio reeiver. The person wathes the eletri and magneti fields go up and down as the wave travels past. After 1 seond, the number of waves that moved past the person is: A: 1 wave B: 3x10 8 waves C: 1.5x10 8 waves D: 6x10 8 waves : Not enough information 8 A radio wave of wavelength 2 meters passes by a person with a radio reeiver. The person wathes the eletri and magneti fields go up and down as the wave travels past. After 1 seond, the number of waves that moved past the person is: A: 1 wave B: 3x10 8 waves C: 1.5x10 8 waves D: 6x10 8 waves : Not enough information 9 3

4 A radio wave of wavelength 2 meters passes by a person with a radio reeiver. The person wathes the and B fields go up and down as the wave travels by. Later, a new radio wave passes the person. They observe that the and B fields go up and down 10 times faster than the original wave. What is the best onlusion? The seond wave A: has a wavelength of 0.2 m B: has a wavelength of 20 m C: travels 10 times faster. D: has 1/10 the frequeny. : More than one (or none of these) is orret. 10 Polarization of Light M waves have a diretion of the letri field vetor. As viewed from an observer: B B 11 Ordinary Light (from the Sun or a lightbulb) is unpolarized, meaning it is a mixture of waves with letri field vetors in random diretions within the plane perpendiular to the wave diretion. Unpolarized Polarized 12 4

5 Polarizer = Polaroid filter = filter that passes light with the -field along the pass axis of the filter only. Polarized Filter Light Passes Through 13 Polarizer = Polaroid filter = filter that passes light with the -field along the pass axis of the filter only. Polarized Filter Light Does Not Pass Through All the M energy is used up as work in moving harged partiles in the filter. 14 If the -field is not all parallel to the pass axis, only the omponent of along the pass axis gets through. θ Only osθ is transmitted. intensity is related to NRGY And thus to field strength squared: Filter Axis S os 2 trans = S 0 (! ) 15 5

6 Cliker Question An unpolarized beam of light passes through a Polaroid filter. The intensity of the original beam is I o. What is the intensity of the light oming through the filter? Io A: (1/1.4)I o B: (1/2)I o C: (1/4)I o D: I o : None of these 16 Cliker Question An unpolarized beam of light passes through 2 Polaroid filters oriented at 45 o with respet to eah other. The intensity of the original beam is I o. What is the intensity of Io the light oming through both filters? A: (1/1.4)I o B: (1/2)I o C: (1/4)I o D: (1/8)I o : None 17 An unpolarized beam of light passes through 3 Polaroid filters, eah oriented at 45 o with respet to eah other. The intensity of the original beam is I o. Does ANY light pass through the last filter? Io A: Yes, some makes it thru B: None makes it thru 18 6

7 a b d Unpolarized light of equal intensity reahes four pairs of polarizing filters. Rank in order, (largest to smallest) the intensities transmitted through the seond polarizer of eah pair. A. a = d > b = B. b = > a= d C. d > a > b > D. d > a > b =. Something else 19 Why do polarizing filter sunglasses work? If sun light is unpolarized, then it just makes things darker by removing one omponent. However, sattering an polarize light. Then the sunglasses work very well at reduing this light (glare). 20 Signal (piture information) is arried by a range of frequenies (Δf = bandwidth ) entered on a arrier frequeny f. Information is enoded either by: Amplitude Modulation (AM) Frequeny Modulation (FM) 21 7

8 v ( x, t) = v B( x, t) = B peak peak sin( kx "! t) yˆ sin( kx "! t) zˆ 22 Who are these people and what do they have in ommon? 23 8