4.Main Content

experiments

A CD (or gramophone record) as a grating

Demonstration or home experiment

Students observe the spectrum produced when light falls obliquely on a CD.

Apparatus and materials

• CD or gramophone record

Safety

Read our standard health & safety guidance

Procedure

Students might like to look at the grating spectra formed by reflection when light falls obliquely on a CD.
 
The rulings are too coarse to be useful at direct incidence. The observer must take an oblique view.
 
If it is a gramophone record, you can calculate the grating spacing. Use a ruler to measure the part of the radius of the grating used. Play it and count the corresponding number of turns.
 
Measuring the grating spacing of a CD will be more challenging.
 
Alternatively, use a known wavelength of light to estimate the grating spacing of a CD.

Teaching notes

This experiment was safety-checked in February 2006