Understanding Electricity and Magnetism: The Atom and Electromagnetic Waves

1. Lecture 5 –The Atom Great Idea:“All matter is made of atoms, which have a positively-charged nucleus surrounded by negatively-charged electrons.”

2. Electricity and magnetism are two aspects of the same force. All magnets have both north and south poles Static electricity is manifest as a force between charged objects Electricity produces magnetic effects. Moving magnets produce electricity.

3. The Electrical Field • The force felt by a charge located at a particular point • Differs from the magnetic dipole field

4. Magnetic Effects from Electricity

5. The Electric Motor North and South poles flip during rotary motion.

6. 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:

7. Maxwell’s Laws, 1855 These equations lead to prediction of waves: 1. Waves travel 186,000 miles per second 2. Light is a consequence of electricity and magnetism switching back and forth

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

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

10. The Relationship Among Wavelength, Frequency, and Velocity velocity of a wave = wavelength x frequency

11. 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)

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

13. Properties of Electromagnetic Waves • Relationship between short & long waves • Short waves = high frequency = high energy • Long waves = low frequency = low energy • Matter interacts with light in 3 ways: • Transparent – light passes through • Absorbing – matter soaks up energy • Scattering – light bounces off

14. Some Matter is Transparent to Light Light waves pass through transparent materials

15. Some Matter Absorbs Light Light waves are absorbed: Materials soak up energy

16. Some Matter Scatters Light Light waves hit and bounce off in many directions

17. Scattering (Reflection)

18. Scattering (Refraction)

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

20. Radio waves • Produced when electrons accelerate • Amplitude increases with amplifier 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

21. Radio Telescope

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

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

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

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

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

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

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

29. Infrared Radiation (Heat)

30. Infrared Radiation (Heat)

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

32. Visible Light

33. Visible Light

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

35. Higher Energy Spectra(Potential Cell Damage) • High energy = short wavelengths • Ultraviolet radiation • Sunblock

36. Higher Energy Spectra(Potential Cell Damage) • High energy = short wavelengths • X-Rays • Medicine

37. Atoms alone • Structure • Periodic Table • Chemical Bonding • Types of bonds • Chemical Reactions • Material Properties [NEXT WEEK] • States of matter • Mechanical & Electrical Properties

38. 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

39. Are Atoms Real?

40. Evidence for Atoms 1. Behavior of gas 2. Ratios of elements

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

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

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

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

45. Is there something smaller? • Rutherford Scintillation Experiments

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

47. Niels Bohr’s Model of the Atom

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

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

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