The nature of

The nature of

…and a history of our attempt to understand it.

Early 1600’sGalileo 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.

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.

http://www.colorado.edu/physics/2000/waves_particles/lightspeed_evidence.html

http://www.google.com/

Early 1600’sGalileo 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.

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.

http://www.colorado.edu/physics/2000/waves_particles/lightspeed_evidence.html


Images acquired at http://en.wikipedia.org/wiki/Olaus_Romer, and http://hubblesite.org/newscenter/newsdesk/archive/releases/1996/30/ through 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.

http://en.wikipedia.org/wiki/Olaus_Romer

http://hubblesite.org/newscenter/newsdesk/archive/releases/1996/30/




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)






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.




1850 Fizeau and Foucault

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

http://laser.phys.ualberta.ca/~egerton/c&ether.htm

http://geocities.yahoo.com.br/saladefisica3/


1850 Fizeau and Foucault

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

Measured c to be about 300,000,000 m/s.

http://laser.phys.ualberta.ca/~egerton/c&ether.htm

http://geocities.yahoo.com.br/saladefisica3/


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://scv.bu.edu/~aarondf/avgal.html through www.google.com.

Light is made of a bunch of little “corpuscles.” (particles)

REFRACTION

http://msp.rmit.edu.au/Article_04/02.html

http://microcosmos.uchicago.edu/microcosmos_new/newton/glassworks/

http://scv.bu.edu/~aarondf/avgal.html


http://microcosmos.uchicago.edu/microcosmos_new/newton/glassworks/introduction.htm

http://scv.bu.edu/~aarondf/Webgifs/prism.gif

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.museum.vic.gov.au/scidiscovery/light/index.asp and http://nobelprize.org/physics/articles/ekspong/ through www.google.com.

Light is a wave.

http://www.fau.edu/~jordanrg/bios/Young/Young_bio.htm

http://www.cavendishscience.org/phys/tyoung/tyoung.htm

http://www.museum.vic.gov.au/scidiscovery/light/index.asp

http://nobelprize.org/physics/articles/ekspong/


http://www.youtube.com/watch?v=3_BzTMeV4HI&feature=related

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.cartref.demon.co.uk/eng/boe20b.jpg through www.google.com.

http://www.tiscali.co.uk/reference/encyclopaedia/hutchinson/m0001235.html

http://dspt.club.fr/FARADAY.htm

http://www.cartref.demon.co.uk/eng/boe20b.jpg


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.cartref.demon.co.uk/eng/boe20b.jpg through www.google.com.

So, a changing magnetic field makes an electric field…

http://www.tiscali.co.uk/reference/encyclopaedia/hutchinson/m0001235.html

http://dspt.club.fr/FARADAY.htm

http://www.cartref.demon.co.uk/eng/boe20b.jpg


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://micro.magnet.fsu.edu/primer/java/electromagnetic/ through www.google.com.

http://www-groups.dcs.st-and.ac.uk/~history/PictDisplay/Maxwell.html

http://home.usit.net/~cmdaven/electro.htm

http://micro.magnet.fsu.edu/primer/java/electromagnetic/



Images acquired at http://www-groups.dcs.st-and.ac.uk/~history/PictDisplay/Maxwell.html and http://home.usit.net/~cmdaven/electro.htm andhttp://micro.magnet.fsu.edu/primer/java/electromagnetic/ through www.google.com.

If a changing magnetic field makes an electric field (or current), wouldn’t a changing electric field make a magnetic field?


http://home.usit.net/~cmdaven/electro.htm

http://micro.magnet.fsu.edu/primer/java/electromagnetic/



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_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.


http://en.wikipedia.org/wiki/Maxwell's_equations


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_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!


http://en.wikipedia.org/wiki/Maxwell's_equations

1905--Albert Einstein and the Photoelectric Effect

Images and acquired at http://sol.sci.uop.edu/~jfalward/particlesandwaves/particlesandwaves.html

http://sol.sci.uop.edu/~jfalward/particlesandwaves/particlesandwaves.html

http://en.wikipedia.org/wiki/Image:Albert_Einstein_1947.jpg


Images and acquired at http://sol.sci.uop.edu/~jfalward/particlesandwaves/particlesandwaves.html

Then light is both!!! (wave and particle)

http://sol.sci.uop.edu/~jfalward/particlesandwaves/particlesandwaves.html

http://en.wikipedia.org/wiki/Image:Albert_Einstein_1947.jpg


Images and acquired at http://sol.sci.uop.edu/~jfalward/particlesandwaves/particlesandwaves.html and http://en.wikipedia.org/wiki/Albert_Einstein through www.google.com.

1921 Nobel Prize (not for Relativity!!!)

Then light is both!!! (wave and particle)

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.

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.

The nature of

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