Conceptual Questions:

1. Why do atoms absorb or emit only limited numbers of wavelengths of electromagnetic radiation?

2. Why do atoms of different elements show different spectra?

3. How does fluorescence work? Phosphorescence?

4. Give an example of chemi-luminescence.

5. What is 'stimulated emission'?

Numerical Problem: help is at the end of the page.

1. Chromium atoms in aluminum oxide form the basis of a ruby laser. There are energy levels in the chromium at 0.0 (the 'ground' state), 1.79, 2.30, and 3.00 eV (1 eV= 1.6 x10^-19 J). The level at 1.79 eV is metastable. What wavelength emerges from the laser?

ans: 694 nm

The wavelength in question radiates as the chromium decays from the metastable state to the ground state. Convert the energy to Joules, and then to frequency with Planck's constant, and then convert frequency to wavelength with the wave formula (v = c).