1. Chapter 24 The Electromagnetic Wave

2. 0) Summary of electromagnetism to Maxwell (1860) Kelvin: lines-of-force to replace action-at-a-distance (Coulomb’s law) Faraday extended idea of fields Maxwell rationalized E&M as stresses and strains in a medium, and tied up the whole field.

4. a) Gauss’s Law A line that doesn’t start or finish inside must leave if it enters.

5. Gauss’s law expresses Coulomb’s law, but valid for moving charges (in free space)

6. b) Gauss’s Law for magnetism (since there are no magnetic monopoles)

7. c) Ampere’s Law (in free space)

8. d) Faraday’s Law Recall so around a loop,

9. a) b) c) d) In free space

10. e) Maxwell’s displacement current I Current through A1 is I current through A2 is zero both are bounded by the loop A1 A2 loop Ampere’s law needs a term for the growing electric field Displacement Current + + + + + + + +

11. (in free space) Recall Faraday’s law: Maxwell looked for a term proportional to

12. f) Maxwell’s Equations in free space

13. g) Solutions to Maxwell’s equations Solution to Maxwell’s equations give Solution to F=ma for constant F is x(t):

14. The concept: Oscillating source -> E changes -> B changes -> E changes…

15. The solution:

16. where Maxwell’s equations predict a disturbance that propogates through empty space at a speed:

17. The conclusion was inescapable: light is “an electromagnetic disturbance in the form of waves” propogated in the ether.

18. 1) Nature of electromagnetic waves Radiation field propogates indefinitely Transverse wave E and B perpendicular to each other and to v No medium needed (speed lower in medium)

19. Reception

21. 2) The electromagnetic spectrum c = f Range of f and is more than 20 orders of magnitude

23. 3) The speed of light Definition: c  299 792 458 m/s exactly Meter  distance light travels in 1/299792458 s (1 second defined by oscillations in Cs)

24. Measurements: –100 BC, Hero of Alexandria, eye blinking: c infinite –Descartes, geometry of eclipse: c infinite

25. –1600, Galileo, lanterns: c > mach 10

26. –1676, Roemer, eclipse of IO: c = 2 x 10 8 m/s

27. –1728, Bradley, stellar aberration: c=3.01x10 8 m/s

28. –1849, Fizeau, toothed wheel: c = 3.13x10 8 m/s

29. –1875, Foucault, rotating mirror: c = 2.99796x10 8 m/s

30. –1878 - 1926, Michelson, rotating mirror: c=2.99796x10 8 m/s