January 26, 2000

Barcodes in the Sun & Stars


 
"Newton's `unweaving' of the rainbow led to spectroscopy, which has proved the key to much of what we know today about the cosmos. And the heart of any poet worthy of the title Romantic could not fail to leap up if he beheld the universe of Einstein, Hubble and Hawking."

Richard Dawkins,"Unweaving the rainbow", 1998 responding to remarks by the poet Keats that Newton destroyed our enjoyment of the rainbow by explaining how it formed. 

Assignments:

Read Chapter  4.3 of your text. Also: HW#1
 Also: How many different "diffraction gratings" (That's an equivalent of a "wave breaker" with 2 openings) are in the spectra-glasses that you got?
Comment about today's tutorial: If you haven't figured it out: The energy levels in the tutorial are the energies of an excited ELECTRON in an ATOM. Transition to a less excited state results in an emission of a photon with energy E=hf. 

Anyone did not get spectra glasses?

Observations start next MONDAY

A new feature: Further explanations.

If I get questions, by Email or in my office hours, that are of interest to the whole class I will post the answers on the Saturday of that week! (See announcements) So if a question that others have problems with - Email me!

Also: People did not have a chance to ask questions. Start now!

Labs, Evening labs &  Tutorial grading: I will be grading labs & tutorials on the following scale (1-10): 
10 - prefect
9 - Some mistakes
7 - obviously incomplete
3 - for coming to lab and submitting something
(Also see announcements)

Waves, spectra   &  some formulas: 
Reminder on board: Wave breaker & "junk piles" (Electro-magnetic field go up & down, strong, in junk piles.)

Shown spectra. Different wavelengths scatter at different angles.

Speed  of a wave: You will see in lab more: 

Speed = distance / time. 

or, for a bunch of waves:

Speed = Wave Length / Period

Or: 

V=l/P
Notice that l is the distance between wave crests and V is the speed of the wave.

Compare with a :

Period = how long it takes to make an up@down.(seconds)

How many up@downs = frequency (1/second or Herz, Hz, like in radio stations)

Q1: How are frequency and period related? Answer 

f=1/P

Using this relationship:

V=  l f

Also: Higher frequencies = higher energy:

Energy of a light particle (photon) = h x speed of light / l

where

h= Planck constant=6.626 x 10-34 Joule x second.

Atoms are the source of "barcode" spectra. To see how this is so, lets do a little tutorial:

What are tutorials? In in-class tutorials we try to have you solve simple problems with help from your instructor. 
Tutorial 1: Light waves from Discharge Arcs & Gasses in Stellar Atmospheres
 

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