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CQ: What does the curve tell you? The spatial extent of the E-field. At the peaks and troughs the E-field is covering a

EM radiation often represented by a sinusoidal curve. OR. CQ: What does the curve tell you? The spatial extent of the E-field. At the peaks and troughs the E-field is covering a larger extent in space The E-field’s direction and strength along the center line of the curve

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CQ: What does the curve tell you? The spatial extent of the E-field. At the peaks and troughs the E-field is covering a

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  1. EM radiation often represented by a sinusoidal curve. OR • CQ: What does the curve tell you? • The spatial extent of the E-field. At the peaks and troughs the E-field is covering a larger extent in space • The E-field’s direction and strength along the center line of the curve • The actual path of the light travels • more than one of these • none of these.

  2. At this time, E-field at point X is strong and in the points upward. Only know E-field, along this line. X EM radiation often represented by a sinusoidal curve. CQ: What does the curve tell you? Correct answer is b. The E-field’s direction and strength along the center line of the curve Path of EM Radiation is a straight line.

  3. Electromagnetic Spectrum Spectrum: All EM waves. Complete range of wavelengths. Wavelength () = distance (x) until wave repeats Also: frequency (f) Hz or sec-1 c = f * l  Blue light  Red light  Cosmic rays SHORT LONG

  4. How much time does it take for E-field at point (X) to go through 1 complete oscillation? a) l/c b) c/l c) 1/l d) l e) none of the above

  5. How much time does it take for E-field at point (X) to go through 1 complete oscillation? a) l/c b) c/l c) 1/l d) l e) none of the above Period (seconds/cycle) = /c f=c Frequency = (1 second)/Period (Hertz) = # of cycles that pass antenna per sec

  6. Oscillating electron at frequency (f) Why is wavelength of generated wave inversely proportional to the frequency of oscillation in antenna?

  7. Electromagnetic waves carry energy Emax=peak amplitude Light shines on black tank full of water. How much energy absorbed? c X E(x,t) = Emaxsin(ax-bt) Intensity = Power = energy/time (Eavg)2 area area  (amplitude of wave)2 Emax2

  8. Maxwell’s Equations: Describes EM radiation E B

  9. HW: Work through solution to 1-D differential equation. E(x,t) = Emaxcos(ax+bt) Show that is a solution. Use boundary conditions to get constants, Emax, a, b. Maxwell’s Equations: Describes EM radiation In 3-D: In 1-D: Read through worked example. Lays out whole process.

  10. c EM radiation is a wave What is most definitive observation we can make that tells us something is a wave? Ans: Observe interference. (peaks are lined up and valleys are lined up) Constructive interference: c

  11. c EM radiation is a wave What is most definitive observation we can make that tells us something is a wave? Ans: Observe interference. (peaks align with valleys – cancel) Destructive interference: c

  12. Two slit interference Wave Interference Sim

  13. The Photoelectric Effect Photoelectric effect: experiment shows light is also a particle. Energy comes in particle-like chunks - basics of quantum physics. Expt: H. Hertz (1887). Theory : Einstein (1905). Nobel 1921.

  14. Photoelectric effect. What is the critical difference between the Hg vapor source and the laser, such that the Hg source gave an effect in photoemission and the laser did not. • The Hg source was closer to the metal plate • The Hg source is brighter than the laser • The Hg source has a shorter wavelength than the laser • The Hg source has a lower frequency than the laser • The lazer was feeling lazey.

  15. Photoelectric effect. What is the critical difference between the Hg vapor source and the laser, such that the Hg source gave an effect in photoemission and the laser did not. • The Hg source was closer to the metal plate • The Hg source is brighter than the laser • The Hg source has a shorter wavelength than the laser • The Hg source has a lower frequency than the laser • The lazer was feeling lazey.

  16. Concept test The “work function” of a metal is a. the amount of work needed to heat up 1 cm3 of that metal by 1 degree C. b. the amount of work produced by the current of electrons emitted from a surface. c. the amount of work needed to produce 1 kg of pure metal from ore. d. the amount of energy required to remove an electron from the metal surface.

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