Didactic activities involving the use of CDs as diffraction grattings are not new. The preparation of simple portable spectroscopes and the projection of spectra for large audiences are some of the suggestions for use. A overhead projector as light source, along with a circular slit, is also suggested. The advantages of this assembly are the very simple interpretation of the diffraction figure obtained. A small change in the assembly suggested here allows for accurate measure of the distance between adjacent tracks of a recordable CD. The didactic dividends can be earned from the exploitation of objects of everyday life (in this case, the CD) goes from active learning to the "resolution" of the everyday objects as generators of reflection, inquiry and awareness.
light diffraction; teaching of optics; optical physics; CD as a diffraction grating; circular slit
