1. The nature of …and a history of our attempt to understand it.

2. Early 1600’s Galileo and the speed of light… Image and info acquired at http://www.colorado.edu/physics/2000/waves_particles/lightspeed_evidence.html through www.google.com.http://www.colorado.edu/physics/2000/waves_particles/lightspeed_evidence.htmlwww.google.com People were saying in the early 1600’s that it took no time for light to travel any distance (speed of light = infinite). Galileo thought otherwise.

3. Early 1600’s Galileo and the speed of light… Image and info acquired at http://www.colorado.edu/physics/2000/waves_particles/lightspeed_evidence.html through www.google.com.http://www.colorado.edu/physics/2000/waves_particles/lightspeed_evidence.htmlwww.google.com People were saying in the early 1600’s that it took no time for light to travel any distance (speed of light = infinite). Galileo thought otherwise.

4. Early 1600’s Galileo and the speed of light… Image and info acquired at http://www.colorado.edu/physics/2000/waves_particles/lightspeed_evidence.html through www.google.com.http://www.colorado.edu/physics/2000/waves_particles/lightspeed_evidence.htmlwww.google.com People were saying in the early 1600’s that it took no time for light to travel any distance (speed of light = infinite). Galileo thought otherwise. Unfortunately for Galileo, light travels a mile in about.000005 s.

5. Images acquired at http://en.wikipedia.org/wiki/Olaus_Romer, andhttp://en.wikipedia.org/wiki/Olaus_Romer, http://hubblesite.org/newscenter/newsdesk/archive/releases/1996/30/http://hubblesite.org/newscenter/newsdesk/archive/releases/1996/30/ through www.google.com.www.google.com 1676 and Olaus Rømer… Rømer was a Danish astronomer who spent some time observing the motion of Io, one of Jupiter’s moons. He noticed that some of Io’s eclipses appeared earlier or later than expected.

6. Images acquired at http://en.wikipedia.org/wiki/Olaus_Romer, andhttp://en.wikipedia.org/wiki/Olaus_Romer, http://hubblesite.org/newscenter/newsdesk/archive/releases/1996/30/http://hubblesite.org/newscenter/newsdesk/archive/releases/1996/30/ through www.google.com.www.google.com 1676 and Olaus Rømer… Rømer was a Danish astronomer who spent some time observing the motion of Io, one of Jupiter’s moons. He noticed that some of Io’s eclipses appeared earlier or later than expected. Then he realized that this was because of the Earth’s position. (see sketch)

7. Images acquired at http://en.wikipedia.org/wiki/Olaus_Romer, andhttp://en.wikipedia.org/wiki/Olaus_Romer, http://hubblesite.org/newscenter/newsdesk/archive/releases/1996/30/http://hubblesite.org/newscenter/newsdesk/archive/releases/1996/30/ through www.google.com.www.google.com 1676 and Olaus Rømer… Rømer was a Danish astronomer who spent some time observing the motion of Io, one of Jupiter’s moons. He noticed that some of Io’s eclipses appeared earlier or later than expected. Then he realized that this was because of the Earth’s position. (see sketch)

8. Images acquired at http://en.wikipedia.org/wiki/Olaus_Romer, andhttp://en.wikipedia.org/wiki/Olaus_Romer, http://hubblesite.org/newscenter/newsdesk/archive/releases/1996/30/http://hubblesite.org/newscenter/newsdesk/archive/releases/1996/30/ through www.google.com.www.google.com 1676 and Olaus Rømer… Rømer was a Danish astronomer who spent some time observing the motion of Io, one of Jupiter’s moons. He noticed that some of Io’s eclipses appeared earlier or later than expected. Then he realized that this was because of the Earth’s position. (see sketch) Measured c to be about 220,000,000 m/s.

9. 1850 Fizeau and Foucault Images acquired at http://laser.phys.ualberta.ca/~egerton/c&ether.htm and http://geocities.yahoo.com.br/saladefisica3/http://laser.phys.ualberta.ca/~egerton/c&ether.htmhttp://geocities.yahoo.com.br/saladefisica3/ through www.google.com.www.google.com

10. 1850 Fizeau and Foucault Images acquired at http://laser.phys.ualberta.ca/~egerton/c&ether.htm and http://geocities.yahoo.com.br/saladefisica3/http://laser.phys.ualberta.ca/~egerton/c&ether.htmhttp://geocities.yahoo.com.br/saladefisica3/ through www.google.com.www.google.com

11. 1850 Fizeau and Foucault Images acquired at http://laser.phys.ualberta.ca/~egerton/c&ether.htm and http://geocities.yahoo.com.br/saladefisica3/http://laser.phys.ualberta.ca/~egerton/c&ether.htmhttp://geocities.yahoo.com.br/saladefisica3/ through www.google.com.www.google.com

12. 1850 Fizeau and Foucault Images acquired at http://laser.phys.ualberta.ca/~egerton/c&ether.htm and http://geocities.yahoo.com.br/saladefisica3/http://laser.phys.ualberta.ca/~egerton/c&ether.htmhttp://geocities.yahoo.com.br/saladefisica3/ through www.google.com.www.google.com

13. 1850 Fizeau and Foucault Images acquired at http://laser.phys.ualberta.ca/~egerton/c&ether.htm and http://geocities.yahoo.com.br/saladefisica3/http://laser.phys.ualberta.ca/~egerton/c&ether.htmhttp://geocities.yahoo.com.br/saladefisica3/ through www.google.com.www.google.com Measured c to be about 300,000,000 m/s.

14. 1704 and Isaac Newton Image acquired at http://msp.rmit.edu.au/Article_04/02.html and http://microcosmos.uchicago.edu/microcosmos_new/newton/glassworks/ andhttp://msp.rmit.edu.au/Article_04/02.htmlhttp://microcosmos.uchicago.edu/microcosmos_new/newton/glassworks/ http://scv.bu.edu/~aarondf/avgal.htmlhttp://scv.bu.edu/~aarondf/avgal.html through www.google.com.www.google.com Light is made of a bunch of little “corpuscles.” (particles) REFRACTION

15. 1801 and Thomas Young Images acquired at http://www.fau.edu/~jordanrg/bios/Young/Young_bio.htm and http://www.cavendishscience.org/phys/tyoung/tyoung.htm andhttp://www.fau.edu/~jordanrg/bios/Young/Young_bio.htmhttp://www.cavendishscience.org/phys/tyoung/tyoung.htm http://www.museum.vic.gov.au/scidiscovery/light/index.asphttp://www.museum.vic.gov.au/scidiscovery/light/index.asp and http://nobelprize.org/physics/articles/ekspong/ through www.google.com.http://nobelprize.org/physics/articles/ekspong/www.google.com Light is a wave.

16. Mid 1800’s and Michael Faraday Experimental Researches on Electricity (1839–55) Image and info acquired at http://www.tiscali.co.uk/reference/encyclopaedia/hutchinson/m0001235.html and http://dspt.club.fr/FARADAY.htm andhttp://www.tiscali.co.uk/reference/encyclopaedia/hutchinson/m0001235.htmlhttp://dspt.club.fr/FARADAY.htm http://www.cartref.demon.co.uk/eng/boe20b.jpghttp://www.cartref.demon.co.uk/eng/boe20b.jpg through www.google.com.www.google.com

17. Mid 1800’s and Michael Faraday Experimental Researches on Electricity (1839–55) Image and info acquired at http://www.tiscali.co.uk/reference/encyclopaedia/hutchinson/m0001235.html and http://dspt.club.fr/FARADAY.htm andhttp://www.tiscali.co.uk/reference/encyclopaedia/hutchinson/m0001235.htmlhttp://dspt.club.fr/FARADAY.htm http://www.cartref.demon.co.uk/eng/boe20b.jpghttp://www.cartref.demon.co.uk/eng/boe20b.jpg through www.google.com.www.google.com

18. Mid 1800’s and Michael Faraday Experimental Researches on Electricity (1839–55) Image and info acquired at http://www.tiscali.co.uk/reference/encyclopaedia/hutchinson/m0001235.html and http://dspt.club.fr/FARADAY.htm andhttp://www.tiscali.co.uk/reference/encyclopaedia/hutchinson/m0001235.htmlhttp://dspt.club.fr/FARADAY.htm http://www.cartref.demon.co.uk/eng/boe20b.jpghttp://www.cartref.demon.co.uk/eng/boe20b.jpg through www.google.com.www.google.com So, a changing magnetic field makes an electric field…

19. Mid 1800’s and Michael Faraday Experimental Researches on Electricity (1839–55) Image and info acquired at http://www.tiscali.co.uk/reference/encyclopaedia/hutchinson/m0001235.html and http://dspt.club.fr/FARADAY.htm andhttp://www.tiscali.co.uk/reference/encyclopaedia/hutchinson/m0001235.htmlhttp://dspt.club.fr/FARADAY.htm http://www.cartref.demon.co.uk/eng/boe20b.jpghttp://www.cartref.demon.co.uk/eng/boe20b.jpg through www.google.com.www.google.com So, a changing magnetic field makes an electric field…

20. James Clerk Maxwell and the 60’s (the 1860’s) Images acquired at http://www-groups.dcs.st-and.ac.uk/~history/PictDisplay/Maxwell.html and http://home.usit.net/~cmdaven/electro.htm andhttp://www-groups.dcs.st-and.ac.uk/~history/PictDisplay/Maxwell.htmlhttp://home.usit.net/~cmdaven/electro.htm http://micro.magnet.fsu.edu/primer/java/electromagnetic/http://micro.magnet.fsu.edu/primer/java/electromagnetic/ through www.google.com.www.google.com

21. James Clerk Maxwell and the 60’s (the 1860’s) Images acquired at http://www-groups.dcs.st-and.ac.uk/~history/PictDisplay/Maxwell.html and http://home.usit.net/~cmdaven/electro.htm andhttp://www-groups.dcs.st-and.ac.uk/~history/PictDisplay/Maxwell.htmlhttp://home.usit.net/~cmdaven/electro.htm http://micro.magnet.fsu.edu/primer/java/electromagnetic/http://micro.magnet.fsu.edu/primer/java/electromagnetic/ through www.google.com.www.google.com If a changing magnetic field makes an electric field (or current), wouldn’t a changing electric field make a magnetic field?

22. James Clerk Maxwell and the 60’s (the 1860’s) Images acquired at http://www-groups.dcs.st-and.ac.uk/~history/PictDisplay/Maxwell.html and http://home.usit.net/~cmdaven/electro.htm andhttp://www-groups.dcs.st-and.ac.uk/~history/PictDisplay/Maxwell.htmlhttp://home.usit.net/~cmdaven/electro.htm http://micro.magnet.fsu.edu/primer/java/electromagnetic/http://micro.magnet.fsu.edu/primer/java/electromagnetic/ through www.google.com.www.google.com If a changing magnetic field makes an electric field (or current), wouldn’t a changing electric field make a magnetic field?

23. James Clerk Maxwell and the 60’s (the 1860’s) Images acquired at http://www-groups.dcs.st-and.ac.uk/~history/PictDisplay/Maxwell.html and http://home.usit.net/~cmdaven/electro.htm andhttp://www-groups.dcs.st-and.ac.uk/~history/PictDisplay/Maxwell.htmlhttp://home.usit.net/~cmdaven/electro.htm http://micro.magnet.fsu.edu/primer/java/electromagnetic/http://micro.magnet.fsu.edu/primer/java/electromagnetic/ through www.google.com.www.google.com If a changing magnetic field makes an electric field (or current), wouldn’t a changing electric field make a magnetic field?

24. James Clerk Maxwell and the 60’s (the 1860’s) Images and quotes acquired at http://www-groups.dcs.st-and.ac.uk/~history/PictDisplay/Maxwell.html and http://en.wikipedia.org/wiki/Maxwell's_equationshttp://www-groups.dcs.st-and.ac.uk/~history/PictDisplay/Maxwell.htmlhttp://en.wikipedia.org/wiki/Maxwell's_equations This velocity is so nearly that of light, that it seems we have strong reason to conclude that light itself (including radiant heat, and other radiations if any) is an electromagnetic disturbance in the form of waves propagated through the electromagnetic field according to electromagnetic laws.

25. James Clerk Maxwell and the 60’s (the 1860’s) Images and quotes acquired at http://www-groups.dcs.st-and.ac.uk/~history/PictDisplay/Maxwell.html and http://en.wikipedia.org/wiki/Maxwell's_equationshttp://www-groups.dcs.st-and.ac.uk/~history/PictDisplay/Maxwell.htmlhttp://en.wikipedia.org/wiki/Maxwell's_equations This velocity is so nearly that of light, that it seems we have strong reason to conclude that light itself (including radiant heat, and other radiations if any) is an electromagnetic disturbance in the form of waves propagated through the electromagnetic field according to electromagnetic laws.

26. James Clerk Maxwell and the 60’s (the 1860’s) Images and quotes acquired at http://www-groups.dcs.st-and.ac.uk/~history/PictDisplay/Maxwell.html and http://en.wikipedia.org/wiki/Maxwell's_equationshttp://www-groups.dcs.st-and.ac.uk/~history/PictDisplay/Maxwell.htmlhttp://en.wikipedia.org/wiki/Maxwell's_equations This velocity is so nearly that of light, that it seems we have strong reason to conclude that light itself (including radiant heat, and other radiations if any) is an electromagnetic disturbance in the form of waves propagated through the electromagnetic field according to electromagnetic laws. So, light must be a wave!

27. 1905--Albert Einstein and the Photoelectric Effect Images and acquired at http://sol.sci.uop.edu/~jfalward/particlesandwaves/particlesandwaves.htmlhttp://sol.sci.uop.edu/~jfalward/particlesandwaves/particlesandwaves.html

28. 1905--Albert Einstein and the Photoelectric Effect Images and acquired at http://sol.sci.uop.edu/~jfalward/particlesandwaves/particlesandwaves.htmlhttp://sol.sci.uop.edu/~jfalward/particlesandwaves/particlesandwaves.html

29. 1905--Albert Einstein and the Photoelectric Effect Images and acquired at http://sol.sci.uop.edu/~jfalward/particlesandwaves/particlesandwaves.htmlhttp://sol.sci.uop.edu/~jfalward/particlesandwaves/particlesandwaves.html Then light is both!!! (wave and particle)

30. 1905--Albert Einstein and the Photoelectric Effect Images and acquired at http://sol.sci.uop.edu/~jfalward/particlesandwaves/particlesandwaves.htmlhttp://sol.sci.uop.edu/~jfalward/particlesandwaves/particlesandwaves.html and http://en.wikipedia.org/wiki/Albert_Einstein through www.google.com.http://en.wikipedia.org/wiki/Albert_Einsteinwww.google.com 1921 Nobel Prize (not for Relativity!!!) Then light is both!!! (wave and particle)

31. In summary… Light: Acts like a particle Acts like a wave Refracts Reflects Diffracts Interferes with itself Has lots of different wavelengths (some visible) Image acquired at http://www.mic-d.com/curriculum/lightandcolor/reflection.html through www.google.com.http://www.mic-d.com/curriculum/lightandcolor/reflection.htmlwww.google.com

32. Light Demonstrations Assignment Your Assignment… In your groups, prepare and perform a physics demonstration that shows the class one or more of these properties of light. Each person will write a description of the demo that contains the following: 1) A sketch of the setup with all parts labeled. 2) A list of materials required. 3) A list of steps to follow to perform the demonstration. 4) Explain which principle this demonstrates and how it demonstrates it. Properties of light: Acts like a particle Acts like a wave Refracts Reflects Diffracts Interferes with itself Has lots of different wavelengths (some visible) Is polarized How cool your demo is will definitely be a factor in your grade on this assignment.