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Dive into the Photoelectric Effect, Quantum Theory, and Atomic Models through the discoveries of pioneers like Einstein and Bohr.

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  1. This Presentation is Brought to YOU by Atomic, Nuclear, and Quantum (IB Physics – Topic 7). my favorite (dr p)

  2. The Photoelectric Effect Discovered by Max Planck and Heinrich Hertz, Germany, in the late 1800’s. Carbon Arc Light • Light from a carbon arc lamp was sent to a metal surface. • If the frequencyof the light is high enough, electrons leave metal surface with KE. • Emitter is connected to negative terminal of a battery. • Collector is attached to positive terminal. Result: The Photocell.

  3. The Explanation of the Photoelectric Effect The emission of electrons from a material that is bombarded with radiation in the form of light. Ephoton = hf with h = 6.6 x 10-34 J ·s LNK2LRN

  4. Contributors to the Photoelectric Effect and Quantum Theory Albert Einstein 1879-1955 Max Planck 1858-1947 Heinrich Hertz 1857-1894 LNK2LRN

  5. Parallel lines, same slope, Planck’s constant, h = 6.6x10-34 J∙s “threshold frequency” for different metals

  6. When red light is incident on a clean metal surface: Clean metal surface e e e e e e • no electrons are released, • No matter how long light shines on it, • No matter how intense the light source is.

  7. When UV light is incident on a clean metal surface: • electrons are released instantaneously, • however weak the light source. UV light e e e e e e e Clean metal surface

  8. Einstein put forth a theory: • Light energy is quantized. • Light consists of a stream of particles called photons. • The energy of each photon (E) depends on the frequency (f ) of the light. h f E=

  9. h is planck's constant red light has a smaller frequency Frequency increasing than violet light

  10. RULE: “One photon per electron, please.” ONE PHOTON GIVES ALL ITS ENERGY TO ONE ELECTRON TO MAKE A PHOTOELECTRON e e

  11. Summary of the Equations for Photoelectric Effect and Quantum Theory E = h·f Energy of a photon of light h = 6.6 x 10-34 J·s Planck’s Constant c = f · Wave equation for light, c = 3.0 x 108 m/s Wo = h·fo Work function, with fo = threshold frequency Maximum kinetic energy of photoelectrons based on stopping potential,Vo KEmax = q·Vo KEmax = E -Wo Maximum kinetic energy of photoelectrons based on photon energy and work function Einstein’s equation for conversion of matter to energy E = mc2

  12. Quick Quiz ! 1. Determine the energy of a single photon in a beam of light of wavelength 451 nm. (a) 2.0 eV (c) 2.8 eV (e) 4.5 eV (b) 2.5 eV (d) 4.2 eV 2. Photons of what minimum frequency are required to remove electrons from gold? Note: The work function for gold is 4.8 eV. (a) 7.3 × 1014 Hz (c) 3.8 × 1017 Hz (e) 4.6 × 1014 Hz (b) 1.2 × 1015 Hz (d) 6.5 × 1015 Hz 3. When ultraviolet photons with a wavelength of 3.45 × 10−7 m are incident on an unknown metal surface in a vacuum, electrons with a maximum kinetic energy of 1.52 eV are emitted from the surface. What is the work function of the metal? (a) 3.60 eV (c) 2.59 eV (e) 1.98 eV (b) 3.11 eV (d) 2.08 eV

  13. History of Atomic Models (I) 1. Single indivisible particle, “atomos” Greek. Democritus(460-370 BC) 2. Plum Pudding Model J.J. Thomson(1856-1940), England, the CRT used to discover the electron.

  14. Apparatus Used to Find m/q for the Electron. Thomson’s CRT (photo) Schematic Drawing

  15. History of Atomic Models (II) 3. Planetary Model - imagine the solar system with the Sun as the nucleus and the planets as the electrons. Ernest Rutherford(1871-1937), England, used the gold-foil experiment to determine that • most of the atom is empty space (2) almost all the mass is in nucleus.

  16. The Rutherford Scattering(Gold Foil) Experiment

  17. Robert Millikan (1868-1953) and his Oil-Drop Experiment in 1909. Proved that the elementary unit of charge, 1.6x10-19 C only occurred in certain amounts (Quantized).

  18. History of Atomic Models (III) 4. Planetary-Quantum model was proposed to align atomic theory with the new physics of Quantum Theory. Niels Bohr(1885-1962), Denmark, determined the equations for rn = 5.29 x 10-11 m x n2 and En = -13.6 eV x 1/n2 n = 1, 2, 3, …

  19. Bohr’s Experiment

  20. The Bohr Model - Planetary Quantum - - - - LNK2LRN

  21. “If waves(light) can act like particles, why can’t particles act like waves”. Proposed for the first time by Prince Louis Victor deBroglie (1892-1987), France. Combine these three equations. E = mc2 c = f · E = h·f Get a single equation for wavelength of a matter particle.  = h /(m∙v) The equation is:

  22. Based on the last discussion, can you then come-up with the equation for the momentum of a photon? Remember, if particles can act like waves, why can’t waves act like particles? The equation is: p = h / Useful constants: 1 eV = 1.6 x 10-19 J mass of electron = 9.11 x 10-31 kg mass of proton = 1.67 x 10-27 kg charge on the electron = -1.6 x 10-19 C charge on the proton = 1.6 x 10-19 C

  23. The Discovery of Radioactivity ALPHA BETA GAMMA Henri Becquerel (1852-1908)

  24. Nuclear Physics.

  25. Contributors to the Study of Nuclear Physics The Nobel Prize in Physics 1903 "in recognition of the extraordinary services they have rendered by their joint researches on the radiation phenomena discovered by Professor Henri Becquerel" "in recognition of the extraordinary services he has rendered by his discovery of spontaneous radioactivity" Antoine Henri Becquerel 1/2 of the prize (France) Pierre Curie   France    1/4 of the prize Marie Curie, née Sklodowska France1/4 of the prize

  26. Nuclear Physics.

  27. Democritus J. J. Thomson Ernest Rutherford Robert Millikan Henri Becquerel E.O. Lawrence Albert Einstein Found charge on electron with Oil-drop experiment Invented the Cyclotron Made the first CRT His equation is E = mc2 Atom is single indivisible particle Gold-foil experiment Radioactive rock fogged photographic plate Matching Exercise.

  28. 5 Particle detectors: • Photographic Film. • Scintillation Screen.

  29. 3. Geiger-Muller Tube. 4. Cloud Chamber. 5. Bubble Chamber.

  30. The Compton Effect the Compton effect is the scattering of a photon off of an electron that’s initially at rest if the photon has enough energy (X-ray energies or higher), the scattering behaves like an elastic collision between particles the energy and momentum of the system is conserved Arthur Compton (1892-1962) 31

  31. The Compton Effect The preceding is a rather messy set of equations to solve … here is the key result: The quantity h/mec is called the Compton wavelength of the electron, and has a value of 2.43x10-12m. PHYS HON, Chapter 27-28: Quantum Theory 32

  32. Example In a Compton scattering experiment, the incident x-rays have a wavelength of 0.2685 nm, while the scattered x-rays have a wavelength of 0.2703nm. Through what angle are the x-rays scattered? h/mec = 2.43x10-12m, the Compton wavelength 33

  33. Performed a series of scattering experiments with a-particles (recall a particles are He nucleus), 42 He + 9 Be 12 C +10 n James Chadwick and the Neutron Circa 1925-1935 Picked up where Rutherford left off with more scattering experiments… (higher energy though!) • Chadwick postulated that the emergent radiation was from a new, neutral particle, the neutron. • Applying energy and momentum conservation he found that the mass of this new object was ~1.15 times that of the proton mass. 1891-1974 Awarded the Nobel Prize in 1935

  34. The Heisenberg Uncertainty Principle “Regardless of how good the measurement apparatus is, it is impossible to measure all of the properties of a particle with arbitrary accuracy at any one time.” • Specifically, position, momentum, and energy, all at the same time Werner Heisenberg (1901-1976)

  35. SCHROEDINGER’S CLOUD THEORY 36 “The task is, not so much to see what no one has yet seen; but to think what nobody has yet thought, about that which everybody sees.“ Erwin Schroedinger (1887-1961) He developed the probability function for the Hydrogen atom (and a few others).  The probability function basically describes a cloud-like region where the electron is likely to be found.  The probable locations of the electron predicted by Schrödinger happen to coincide with the locations specified in Bohr's model.

  36. 1. An isotope has the same value of a. mass number b. neutron number c. atomic number d. nucleon number e. nucleon number and neutron number 2. The isotope, tritium, has a half-life of 12 years. Assume we have 10 kg of the substance. How much tritium will be left after 48 years? a. .20 kg b. 1.8 kg c. .63 kg d. 1.7 kg e. 1.7 kg 3. Radioactive nuclei can decay spontaneously by emitting the following particles: a. helium nuclei, high-speed electrons, photons b. electrons, neutrons, molecules c. helium nuclei, electrons, cyclotrons d. electrons, carbons, photons e. quarks and gamma Quick Quiz

  37. NUCLEAR FUSION : Joining atoms. 1H2 + 1H3 2He4 + 0n1 + 17.59 MeV

  38. 4. The smallest particle of any chemical element that can exist by itself and yet retain the qualities that distinguish it as that element is: A. an electron B. a proton C. a neutron D. an atom E. a molecule 5. The mass of an electron: A. is almost the same as that of a neutron B. is negative C. equals that of a proton D. is zero if the electron is at rest E. is much less than that of a proton 6. The mass of a neutron in amu’s: A. exactly equals that of an electron B. exactly equals that of a proton C. is a little more than that of a proton D. is exactly that of a proton plus an electron E. is as yet unmeasured Quick Quiz

  39. A Nuclear Reactor Used to Boil Water for a Steam Turbine (

  40. A Nuclear Reactor Used to Generate Electricity

  41. 7. The atomic number of an element is: A. the whole number nearest to its mass B. the number of protons in its nucleus C. the total number of protons and neutrons in its nucleus D. the number of neutrons in its nucleus E. its order of discovery on the Periodic Table 8. Iron has atomic number 26. Naturally mined iron contains isotopes of mass numbers 54, 56, 57, and 58. Which of the following statements is FALSE? A. Every atom of iron has 26 protons B. Some iron atoms have 30 neutrons C. Some iron atoms have 54 neutrons D. Iron is most stable 9. A femtometer is: A. larger than 10−9 m B. 10−9 m C. 10−12 m D. 10−15 m E. 10−18 m Quick Quiz

  42. What Happened at Chernobl. 1. Steam Explosion. 2. Partial Meltdown. 3. Containment held.

  43. 10. The half-life of a radioactive substance is: A. half the time it takes for the entire substance to decay B. usually about 50 years C. the time for radium to change into lead D. calculated from E = mc2 E. the time for half the substance to decay 11. The half-life of radium is about 1600 years. If a rock initially contains 1000 g of radium, the amount left after 6400 years will be about: A. 938 g B. 63 g C. 31 g D. 16 g E. less than 16 g 12. Radioactive 90Sr has a half-life of 30 years. What percent of a sample of 90Sr will remain after 60 years? A. 0% B. 25% C. 50% D. 75% E. 14% Quick Quiz

  44. The Linear Accelerator was invented by John Cockcroft and E. T. S. Walton at the Cavendish Laboratory, Cambridge, England, in the late 1920s

  45. The Nobel Prize in Physics 1939 Awarded to E.O. Lawrence, Univ. of California, Berkeley "for the invention and development of the Cyclotron and for results obtained with it, especially with regard to artificial radioactive elements"

  46. The “Marie Curie’s” of Today Women In Physics • Her work involved slowing down light to 17m/s in an ultra-cold gas. • Did 7 months at CERN, the European Laboratory for Particle Physics near Geneva. • From Netherlands, now teaches at Harvard. • “After I discovered quantum physics, I've been hooked ever since.I would rather do physics than go to the movies.” Lene Vestergaard

  47. Women In Physics • Born in Hong Kong • “Reading the biography of Marie Curie inspired me so much that I decided to devote my life to physics.” • Graduated from Vassar summa cum laude and Phi Beta Kappa, and then earned her Ph.D. from Harvard. • Working at MIT, she was a member of the team that discovered a new particle known as J/psi, or the charm quark. • She played a key role in the discovery of the gluon, the “particle that holds quarks together to form protons and neutrons.” Sau Lan Wu

  48. Women In Physics • She was the 1st tenured woman in physics at Princeton; the 1st tenured woman theorist in Physics at Harvard & MIT. • She's the most cited theoretical physicist in the world in the last five years. • Research in theoretical high energy physics. • “I really like that my work is getting more people interested in Physics.” Lisa Randall

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