1. + + + +

2. + + + + +

3. Rutherford’s Model of the Atom+
Most of the atom is empty space.
Most of the atom’s mass and + charge is located at the center of the atom.

4. Next Bohr’s model How a laser works X-ray production
Wave-particle duality
Quantum Physics

5. Exercise
A radiostation broadcasts at 89.3 MHz with a radiated power of 43.0 kW.
What is the magnitude of the momentum of each photon?
How many photons does the radiostation emit each second?

6. Exercise
For a certain cathode material in a photoelectric-effect experiment you measure a stopping potential of 1.0V for light for wavelength 600nm, 2.0 V for 400 nm, and 300nm for 300nm. Determine the work function for this material and the value of Planck’s constant.

7. Emission spectral

8. Things to consider Unique spectral lines for each element.
Each spectral line has a particular frequency => particular photon energy
Heavy positively charge nucleus in the center of the atom arounded by electrons.

9. Attraction between negative electrons and positived nucleus.
Rutherford’s proposal - - + - - -

10. Bohr’s model
Electrons move around the nucleus at stable orbits without emitting radiation.
Electron in one of these stable orbit has a definite energy.
Energy is radiated only when electrons make transitions from high energy orbit to a low energy orbit.

11. hf +

12. hf +

13. Energy is emitted as photons with energy+ - -

14. Quantifying the energy spectrum
Bohr postulate that the angular momentum of an electron revolving around a nucleus is quantized in units of h/2p

15. Newton’s 2nd law yields

16. The smallest radius is obtained by setting n = 1, is called the bohr radius.

17. Kinetic energy of moving electrons

18. Potential energy of electron bound to + nucleus

19. Total energy of electron n-th orbital

20. Energy level diagram
The possible energies which electrons in the atom can have is depicted in an energy level diagram.

21. Bohr’s model and the operation of the Laser
In 1958, Charles Townes and Arthur Schawlow theorized about a visible laser, an invention that would use infrared and/or visible spectrum light.
Light Amplification by Stimulated Emission of Radiation- (LASER).
Properties of Lasers
Produce monochromatic light of extremely high intensity.

22. Bohr’s model and the operation of the Laser

23. Bohr’s model and the operation of the Laser
(Pumping the Laser)

24. Bohr’s model and the operation of the Laser

25. Bohr’s model and the operation of the Laser

26. Bohr’s model and the operation of the Laser

27. Bohr’s model and the operation of the Laser

28. Bohr’s model and the operation of the Laser

29. Bohr’s model and the operation of the Laser

30. Bohr’s model and the operation of the Laser

31. Bohr’s model and the operation of the Laser

32. X-ray production Properties of x-rays.
High penetration => High energy =>High frequency.
X-rays are produced when acelerated electrons strike a heavy metalic target (W).

33. Operation of an X-ray machine

34. X-ray production on the atomic scale

35. X-ray production on the atomic scale

36. ALLAN MACLEOD CORMACK : 1924-1998
Lecturer in Physics, University of Cape Town,
Nobel Prize for Physiology and Medicine, 1979
Development of the CAT scanner (Computer Aided Tomography).

37. SIR AARON KLUG
MSc student in Physics, University of Cape Town, 1946?
Nobel Prize for Chemistry 1982
Probing the properties of macromolecules (DNA) with x-rays.

38. Wave-Particle Duality
In the Bohr model, electrons orbit the atomic nucleus in stable orbits.
What makes an orbit stable?
Louis de Broglie proposed that subatomic particles, such as electron, could exhibit some wave behaviour.

39. De Broglie’s Wave Particle Model
Similar to photons
Wavelength of particle is related to its momentum by

40. where

41. Bohr’s model with wavy electrons
An electron orbit is stable if an integer number of de Broglie standing wave can fit into it. +

42. General

43. Yields

44. Wave Phenomenon Phenomenon associated with waves include:
Interference effects
Reflection
Refraction

45. Interference
Superposition of wave pulse

46. Davidson-Germer experiment
Aim: to test if particle (electrons) exhibit properties of waves i.e. Inteference.
Young’s experiment to find interference pattern due to particle wave interaction.

47. ?

48. Electron diffraction pattern

49. Scanning electron microscope images

51. Theory of Quantum mechanics
Understanding the nature of the particle waves.
Heisenbergs uncertainty principle
Schroedinger’s equation.
Spin-off of quantum theory in the today’s world

52. Quantum Scale

53. Heisenbergs Uncertainty Principle
On the scale on life size object a system is not influenced by measurements on a system (Deterministic system).
On the atomic scale a measurement on a system will influence on it.

54. Finding the location of an electron-

55. Finding the location of an electron-

56. The Uncertainty Principle
Act of measurement influences the electron’s state
Neither the position nor the momentum of a particle can be determined with arbitrary great precision

57. Schroedinger’s Wave Equation

58. Heisenberg Uncertainty + de Broglie waves = Schroedinger’s probabily waves function

59. Schroedinger’s solution to the electron orbitals in the atom