An atom has three valence electrons in a p shell. Determine the total number of states in this configuration.
That is, how many distinct three electron states can be constructed from the orbits in a p shell?
8
3
20
12
4
The laboratory operation of a Laser is related to the atomic transition problem. Let $E_2 - E_1 = i\omega$ for two
atomic states, $u(\omega)$ be the radiation density, $N_1$ be the number of atoms in state 1, and $N_2$ that in state 2.
$B_{12}$ is the Enstein coffeicent for absorption, $B_{21}$ that transition probability for emission, and $A$ the
spontaneous emission coefficient. Find $N_2/N_1$
$B_{12}u(\omega)/A$
$B_{12}u(\omega)/[A + B_{21}u(\omega)]$
$Au(\omega)/B_{12}$
$B_{12}/[A + B_{21}]$
$B_{12}u(\omega)/B_{21}$
