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

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. Review – Maxwell ’ s Equations for Electricity & Magnetism.

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

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  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

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