Great Ideas in Science: Lecture 5 – Electromagnetic Radiation and the Atom

1. Great Ideas in Science:Lecture 5 – Electromagnetic Radiation and the Atom Professor Robert Hazen UNIV 301 Great Idea: All matter is made of atoms which have a positively-charged nucleus surrounded by negatively-charged electrons.

2. Review – Maxwell’s Equations for Electricity & Magnetism • Coulomb’s law of static electricity • All magnets have both North and South poles • Electricity produces magnetic fields • Moving magnets produce electricity

3. Review – Maxwell’s Equations for Electricity & Magnetism Maxwell’s prediction of many kinds of electromagnetic radiation

4. Energy Transfer by Waves • Waves • Carry energy • Matter doesn’t move • Properties of Waves • Wavelength • Frequency • Velocity • Amplitude

5. Properties of Electromagnetic Waves • Wavelength (e.g. crest to crest) – Any value • Frequency (number per second) – Any value • Speed = 300,000 kilometers per second = 186,000 miles per second • Amplitude (height of the wave)

6. Energy Transfer by Waves • Properties of Waves • Wavelength • Frequency • Velocity • Amplitude

7. Electromagnetic Spectrum • Diagram of EM spectrum (w/ color)

8. Properties of Electromagnetic Waves • Relationship between short & long waves • Shorter waves = high frequency = high energy • Long waves = low frequency = low energy • Light interacts with matter by: • Transmission – light passes through • Absorption – matter soaks up energy • Scattering – light bounces off

9. Scattering Light waves hit and bounce off in many directions

10. Scattering (Reflection)

11. Scattering (Refraction)

12. Transmission Light waves pass through transparent materials

13. Absorption Light waves are absorbed: Materials soak up energy

14. Radio waves • Produced when electrons accelerate • Higher amplitude = more tower power • Most everyday objects are transparent to radio waves • Walls, ceiling, windows, doors • Metals absorb radio waves • That’s why antennas are made of metal • What scatters radio waves? • Ionosphere, especially at night

15. Radio Telescope

16. Amplitude Modulation (AM) • Carrier waves • Modulated signal by altering amplitude • Analogous to turning a flashlight off and on

17. Frequency Modulation (FM) • Carrier waves • Modulated signal by altering frequency • Analogous to switching a flashlight from yellow to blue

18. Microwaves 3 major uses in our society • Cooking (Ovens)

19. Microwaves 3 major uses in our society • Cell phones (point-to-point communications)

20. Microwaves 3 major uses in our society • Radar (stealth technology)

21. Infrared Radiation (Heat)

22. Infrared Radiation (Heat)

23. Visible Light

24. Higher Energy Spectra(Potential Cell Damage) • High energy = short wavelengths • Ultraviolet radiation • Sunblock • X-Rays • Medicine

25. Brahe & Kepler Planetary Motions 1 & 2 Galileo Motions on Earth 1 & 2 Newton: Laws of Motion and Gravity 2 Energy Thermodynamics 3 Electricity & Magnetism 4

26. Energy Thermodynamics 3 Electricity & Magnetism 4 Electromagnetic Radiation 5 The Atom Materials 5-6 Quantum Mechanics 6

27. Atoms alone • Structure • Electron energies (shells) • Quantum mechanics • Periodic Table • Chemical Bonding • Magic numbers • Types of bonds • Chemical Reactions • Material Properties • States of matter • Mechanical Properties • Electrical Properties

28. The atom GREAT IDEA: All matter is made of atoms which have a positively-charged nucleus surrounded by negatively-charged electrons. KEY WORDS: • Atom • Proton • Neutron • Electron • Atomic Number • Nucleus • Ion • Periodic Table of Elements

29. Are Atoms Real?

30. Evidence for Atoms 1. Behavior of gas 2. Ratios of elements 3. Radioactivity 4. Brownian Motion – Einstein

31. Evidence for Atoms 5. Avogadro's number (6.0221415 x 1023) 6. X-ray diffraction 7. Atomic microscopy

32. Is there something smaller? • Electron (J. J. Thompson)

33. Is there something smaller? • Electron (J. J. Thompson) • Negatively charged • Easily stripped off atoms • Mass is negligible

34. Is there something smaller? • Rutherford Scintillation Experiments

35. Is there something smaller? • Rutherford Scintillation Experiments • Atomic “bullets” hit gold foil • A few bounce backwards • Reveals tiny but massive atomic nucleus

36. Niels Bohr’s Model of the Atom

37. Niels Bohr’s Model of the Atom Electrons occur in fixed energy levels (shells)

38. Bohr Model of the Atom Electron energy levels are analogous to standing waves

39. Bohr Model of the Atom Changes levels = Quantum leaps Photon = single light wave emitted

40. Properties of Electromagnetic Waves Light interacts with matter by: • Transmission – light passes through • Absorption – matter soaks up energy • Scattering – light bounces off

41. Quantum Mechanics • At the scale of atoms, everything comes in “quanta” (bundles). • You can’t measure a property without changing the object being measured. • Every measurement requires: • A sample, • A source of energy, • A detector.

42. Spectroscopy Measure the wavelength and intensity of light

43. Spectroscopy Measure the wavelength and intensity of light

44. Spectroscopy Measure the wavelength and intensity of light

45. Absorption of Light

46. Fluorescence – black light

47. Fluorescence – black light

48. Lasers

49. Is There Any Order tothe Different Kinds of Atoms? Dimitri Mendeleev ca. 1867

50. Periodic Table of the Elements