Maxwell's Equations and Electromagnetic Radiation: Understanding Light and Waves, Study notes of Physics

Download Maxwell's Equations and Electromagnetic Radiation: Understanding Light and Waves and more Study notes Physics in PDF only on Docsity! 1 1 Where does the word "laser" come from? A: The name of the physicist who invented it. B: The name of the dog of the physicist who invented it C: "Light Amplification by Stimulated Emission of Radiation" D: It's a mix of "light" and "phaser" E: It was just made up because it sounded cool 2 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 participation available - don’t forget about it! _________________________ Last: Maxwell's equations, light, and EM radiation Today: More of Maxwell and EM radiation Next: Waves, LC circuits and resonance. (Prof. Gurarie) 3 Maxwell’s equations. The axioms of electromagnetism. They are one of the major triumphs of modern science! ! r E • d v A "" =Qenclosed /#0 r B • d v A "" = 0 r E • d r l = $ d%B dt " r B • d r l = µ 0 ithrough + µ0#0 d%E dt " 2 4 Visible Light: Example: Yellow light Frequency = 5E14 Hz λ = 500-550 nm (yellow) 5 Traveling wave x (position)λ f λ = c λ /T = c Wavelength 6 Visible Light: λ= 400 nm (violet)  700 nm (red) Example: λ = 550 nm (yellow) f = c/λ = 3x108/550x10-9 = 5x1014 Hz f λ = c 5 13 Polarizer = Polaroid filter = filter that passes light with the E-field along the “pass axis” of the filter only. c Polarized E Filter Light Passes Through… 14 c Polarized E Filter Light Does Not Pass Through… All the EM energy is used up as work in moving charged particles in the filter. Polarizer = Polaroid filter = filter that passes light with the E-field along the “pass axis” of the filter only. 15 If the E-field is not all parallel to the pass axis, only the component of E along the pass axis gets through. Eθ Filter Axis Only Ecosθ is transmitted. intensity is related to ENERGY And thus to field strength squared: )(cos20 !SStrans = 6 16 An unpolarized beam of light passes through a Polaroid filter. The intensity of the original beam is Io. What is the intensity of the light coming through the filter? A: (1/1.4)Io B: (1/2)Io C: (1/4)Io D: Io E: None of these Io c Clicker Question 17 An unpolarized beam of light passes through 2 Polaroid filters oriented at 45o with respect to each other. The intensity of the original beam is Io. What is the intensity of the light coming through both filters? A: (1/1.4)Io B: (1/2)Io C: (1/4)Io D: (1/8)Io E: None Io c Clicker Question 18 An unpolarized beam of light passes through 3 Polaroid filters, each oriented at 45o with respect to each other. The intensity of the original beam is Io. Does ANY light pass through the last filter? A: Yes, some makes it thru B: None makes it thru Io c 7 19 A. a = d > b = c B. b = c > a= d C. d > a > b >c D. d > a > b = c E. Something else Unpolarized light of equal intensity reaches four pairs of polarizing filters. Rank in order, (largest to smallest) the intensities transmitted through the second polarizer of each pair. a b c d 20 Why do polarizing filter sunglasses work? If sun light is unpolarized, then it just makes things darker by removing one component. However, scattering can polarize light. Then the sunglasses work very well at reducing this light (glare). 21 Signal (picture information) is carried by a range of frequencies (Δf = “bandwidth”) centered on a “carrier frequency” f. Information is encoded either by: Amplitude Modulation (AM) Frequency Modulation (FM)