Chap. 4 Origin and Nature of Light

Blackbody Radiation

Blackbodies - absorbs all the EM that strikes it

the intensity of each wavelength emitted is determined by its temperature

Wien’s Law - the dominant wavelength of EM emitted by a BB is inversely proportional to its temp.

l max = 2.9 x 10¯3 / T T in Kelvin

Stefan - Boltzmann Law - an object emits E at a rate proportional to the fourth power of its temp in Kelvins.

F = s T4 F is Energy Flux “rate of flow”
s = 5.67 x 10¯8 J/(m2K4s)

We can find the total E emitted (Luminosity) using

L = s T4 41r2
This allows us to compare stars (p.89)

The solar spectrum contains fine dark lines called spectral lines

Each Chemical element produces its own characteristic pattern of spectral lines

Spectroscope - optical device used to examine spectra when you photograph them - spectrographs

Kirchhoff’s Laws
1. A hot object or a hot, dense gas produces a continuous spectrum - rainbow

2. A hot, rarefied gas produces an emission line spectrum - bright spectral lines against a black background

3. A cool gas in front of a continuous source of light produces an absorption line spectrum - a series of dark lines among a rainbow background.

So What Causes these spectral lines???
They are caused by electrons moving from energy level to energy level

dark lines indicate absorption

bright lines indicate emission

The Doppler Shift or Officer I wasn’t speeding

D l/l = v/c

red vs blue shift -> not just a fashion statement anymore

radial vs. proper motion (OH)

Chp. 4 - # of 3