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Aim: How can we apply mathematics to the photoelectric effect?

Aim: How can we apply mathematics to the photoelectric effect?. In the photoelectric effect, how do you increase: The number of ejected electrons? The KE of the ejected electrons?. Increase intensity of the wave Increase frequency of the wave.

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Aim: How can we apply mathematics to the photoelectric effect?

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  1. Aim: How can we apply mathematics to the photoelectric effect? In the photoelectric effect, how do you increase: The number of ejected electrons? The KE of the ejected electrons? Increase intensity of the wave Increase frequency of the wave

  2. http://www.stmary.ws/highschool/physics/home/animations3/modernPhysics/photoelectricEffect.htmlhttp://www.stmary.ws/highschool/physics/home/animations3/modernPhysics/photoelectricEffect.html

  3. Wave-Particle Duality • According to Einstein, light has particle characteristics • Light travels as a photon Photon – A “bundle” or “packet” of energy Has zero rest mass but has momentum and energy Albert Einstein 1879 – 1955

  4. Momentum • Previously learned p = mv • You need mass to have momentum • Photons have no mass but have momentum • Contradicts classical physics!

  5. The Planck Hypothesis • In 1900, Max Planck proposed that energy could exist only in discrete quanta which were proportional to the frequency. Max Planck 1858 - 1947

  6. = Ephoton = energy of a photon measured in J or eV

  7. Slope = h max KE of ejected electrons fo frequency

  8. Also….

  9. How much energy does a photon of yellow light have? Ephoton = hf Ephoton = (6.63 x 10-34 J·s)(5.20 x 1014 Hz) Ephoton = 3.45 x 10-19 J How many electrons will be ejected if the threshold frequency is 6.20 x 1014 Hz? None – If the frequency is below the threshold frequency, no electrons get ejected

  10. Minimum Energy • The minimum frequency gives the minimum energy • Minimum frequency = threshold frequency (fo) • Minimum energy = work function (Wo) Can you figure out the formula for work function? Wo = hfo

  11. What is the work function of zinc if the threshold frequency is 9.6 x 1014 Hz? Wo = hfo Wo = (6.63 x 10-34 J·s)(9.6 x 1014 Hz) Wo = 6.4 x 10-19 J

  12. KE Model for the Ejected Photoelectrons Photon KEmax Ephoton = hf Wo = hfo e- e- e- e- e- e- Photoelectrons

  13. Formula KEmax = Ephoton – Wo KEmax = hf – hfo KEmax = h(f – fo)

  14. Light with a frequency of 4.5 x 1015 Hz strikes zinc whose work function is 6.4 x 10-19 J. What is the maximum kinetic energy of the ejected electrons? KEmax = hf – Wo KEmax = (6.63 x 10-34 J·s)(4.5 x 1015 Hz) – 6.4 x 10-19 J KEmax = 3.0 x 10-18 – 6.4 x 10-19 KEmax = 2.34 x 10-18 J

  15. The work function of chromium is 4.6 eV. If a photon with 5.0 eV of energy strikes chromium, what is the maximum kinetic energy of the ejected electrons? KEmax = Ephoton – Wo KEmax = 5.0 eV – 4.6 eV KEmax = 0.4 eV Convert this to Joules.

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