1. Ast 1001 -- 25 October 2007 The Nature of Light (This topic is a little out of order; we’ll return to the Solar System later)

2. Ast 1001 -- 25 October 2007 ELECTROMAGNETIC WAVES = “ELECTROMAGNETIC RADIATION” JAMES CLERK MAXWELL, 1864:

3. Ast 1001 -- 25 October 2007

4. FREQUENCY = NUMBER OF WAVE CRESTS PER SECOND.

5. Ast 1001 -- 25 October 2007 FREQUENCY = NUMBER OF WAVE CRESTS PER SECOND. IF A WAVE MOVES AT SPEED c, THEN FREQUENCY = c / WAVELENGTH or WAVELENGTH = c / FREQUENCY.

6. Ast 1001 -- 25 October 2007 FREQUENCY = NUMBER OF WAVE CRESTS PER SECOND. IF A WAVE MOVES AT SPEED c, THEN FREQUENCY = c / WAVELENGTH or WAVELENGTH = c / FREQUENCY. HIGH FREQUENCY MEANS SHORT WAVELENGTH.

7. Ast 1001 -- 25 October 2007 THE ELECTROMAGNETIC SPECTRUM GAMMA RAYS X-RAYS ULTRAVIOLET LIGHT ( UV ) VISIBLE LIGHT ( VIOLET TO RED ) INFRARED LIGHT ( IR ) MILLIMETER WAVES RADIO ( INCLUDING MICROWAVES )

8. Ast 1001 -- 25 October 2007

9. 1900—1905, MAX PLANCK AND ALBERT EINSTEIN: LIGHT CAN BE REGARDED AS PARTICLES AS WELL AS WAVES. “QUANTA” “PHOTONS”

10. Ast 1001 -- 25 October 2007 1900—1905, MAX PLANCK AND ALBERT EINSTEIN: LIGHT CAN BE REGARDED AS PARTICLES AS WELL AS WAVES. ENERGY OF A PHOTON = h X FREQUENCY -- where h is a universal quantity called “Planck’s constant”.

11. Ast 1001 -- 25 October 2007 HIGHER-ENERGY LOWER-ENERGY PHOTONS PHOTONS

12. Ast 1001 -- 25 October 2007 Mention how E.M. waves / radiation affect matter, and vice-versa: continuous electric waves, vs. sudden impacts ( see next slide )

13. Ast 1001 -- 25 October 2007

15. Next: SPECTRA

16. Ast 1001 -- 25 October 2007

17. Three concepts to remember... CONTINUOUS SPECTRUM ABSORPTION LINES EMISSION LINES

18. Ast 1001 -- 25 October 2007 SPECTRAL LINES DEPEND ON THE CHEMICAL ELEMENT ( atoms or molecules )

19. Ast 1001 -- 25 October 2007 NEILS BOHR’S THEORY OF THE HYDROGEN ATOM (1913)

20. Ast 1001 -- 25 October 2007

21. REAL ATOMS ARE MORE LIKE THIS: QUANTUM PHYSICS “WAVE FUNCTIONS”.

22. Ast 1001 -- 25 October 2007 ATOMIC ENERGY LEVELS

23. Ast 1001 -- 25 October 2007 ENERGY LEVELS OF HYDROGEN

24. Ast 1001 -- 25 October 2007 ATOMIC ENERGY LEVELS

25. Ast 1001 -- 25 October 2007

26. E.M. RADIATION EMITTED BY OPAQUE SURFACES...

27. Ast 1001 -- 25 October 2007

29. HIGHER TEMPERATURE implies HIGHER AVERAGE PHOTON ENERGIES implies SHORTER WAVELENGTHS (“bluer”)

30. Ast 1001 -- 25 October 2007 HIGHER-ENERGY LOWER-ENERGY PHOTONS PHOTONS

31. Ast 1001 -- 25 October 2007 Some examples... “ROOM TEMPERATURE” (~ 300 °K): INFRARED.

32. Ast 1001 -- 25 October 2007 Some examples... “ROOM TEMPERATURE” (~ 300 °K): INFRARED. 3000—10000 °K: VISIBLE LIGHT.

33. Ast 1001 -- 25 October 2007 Some examples... “ROOM TEMPERATURE” (~ 300 °K): INFRARED. 3000—10000 °K: VISIBLE LIGHT. 40,000 °K: ULTRAVIOLET.

34. Ast 1001 -- 25 October 2007 Some examples... “ROOM TEMPERATURE” (~ 300 °K): INFRARED. 3000—10000 °K: VISIBLE LIGHT. 40,000 °K: ULTRAVIOLET. 10 million degrees: X-RAYS.

35. Ast 1001 -- 25 October 2007 Some examples... “ROOM TEMPERATURE” (~ 300 °K): INFRARED. 3000—10000 °K: VISIBLE LIGHT. 40,000 °K: ULTRAVIOLET. 10 million degrees: X-RAYS. ( Caution: These are the average wavelengths. )

36. Ast 1001 -- 25 October 2007