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Waves, Light, Quantum

Waves, Light, Quantum. (a few more recently discovered elements added). Figure 4.1: Molar Volume. (elements known in 1869). Other Periodic Trends. View of White Light Through Spectroscope (Investigate This 4.5). white light viewed through slit. light separated into different wavelengths

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Waves, Light, Quantum

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  1. Waves, Light, Quantum

  2. (a few more recently discovered elements added) Figure 4.1: Molar Volume (elements known in 1869)

  3. Other Periodic Trends

  4. View of White Light Through Spectroscope (Investigate This 4.5) white light viewed through slit light separated into different wavelengths by diffraction grating

  5. KMnO4 View of White Light Source Through KMnO4 Solution (Investigate This 4.5) white light source white light source covered with permanganate solution

  6. Color of Wavelengths Absorbed is Complementary To Color Observed Purple Appearing Light

  7. Emission vs. Absorption(Consider This 4.7) prism (wavelength separator) light source some matter (light absorber) white light source

  8. Light = Electromagnetic Waves Electromagnetic radiation the emission and transmission of energy in the form of electromagnetic waves

  9. one cycle wavelength amplitude Properties of Waves • = wavelength = length of one cycle n = frequency = number of cycles/time

  10. Properties of Waves l x n = c c = velocity of light wave in vacuum = 3.00 x 108 m/s

  11. l = c/n l = (3.00 x 108 m/s) / 4.69 x 1014 Hz l = 6.40 x 10-7 m Problem 4:A laser used to weld detached retinas produces light with frequency of 4.69 x 1014 Hz. What is this wavelength in nm? To what part of the electromagnetic spectrum does this light belong? (1Hertz = 1 s-1.) l = 640 nm (red region of visible spectrum)

  12. Waves In a Ripple Tank(Investigate This 4.12, 4.16) • Click on ripple tank wave simulation • For 4.12 • Set to Setup: Single Source; 1 Src, 1 Freq; Color Scheme 3 • For 4.16 • Change Setup to Double Slit (source automatically switches to 1 Plane Src, 1 Freq)

  13. Planck’s Quantum Theory

  14. state 3 state 2 E state 1 Classical Physics View continuous E states Planck’s Quantum View quantized E states Planck’s Basic Ideas • E states of a system (e.g., atom) are quantized, not continuous

  15. state 3 state 2 E state 1 Classical Physics View continuous E states infinite #of DE possible Planck’s Quantum View only transitions allowed are between quantized E states Planck’s Basic Ideas • Only certain E increments may be absorbed or emitted by system emissions

  16. E state 3 state 2 DE3˝1 = hn state 1 Planck’s Basic Ideas • Energy is emitted or absorbed in discrete units (quanta) DE = hn (Planck’s Law) h = 6.63 x 10-34 J•s

  17. hn e- 7.1 The Photoelectric Effect • Light strikes metal surface and ejects an electron • Classical physics predicts light intensity determines if e- is ejected. • But e- is ejected only if light of minimumn (no) is used; intensity does not matter.

  18. The Photoelectric Effect

  19. Ephoton = hn e- e-removed oo oo oo Ee- 1 e- in metal 1 1 Ephoton = DEe- e- ejected Ephoton > DEe- e- ejected with kinetic energy Ephoton < DEe- e- not ejected Einstein: Quantum Theory Explains the PE Effect • Light is a stream of photons

  20. oo Ee- 1 DE1˝ oo= hno What is no?(What is n needed to eject e-?) • How much E must the e- absorb if it moves from n=1 to n=oo? • DEe- = Ee-,n=oo - Ee-,n=1 • This increase in Ee- is supplied by the photon • DEe- = Ephoton = hnoor no = DEe-/h

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