A CD or gramophone record as a grating

Demonstration

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

Apparatus and Materials

CD or gramophone record

Health & Safety and Technical Notes

Read our standard health & safety guidance

Procedure

1. Students might like to look at the grating spectra formed by reflection when light falls obliquely on a CD.
2. The rulings are too coarse to be useful at direct incidence. The observer must take an oblique view.
3. 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.
4. Measuring the grating spacing of a CD will be more challenging.
5. Alternatively, use a known wavelength of light to estimate the grating spacing of a CD.

Teaching Notes

This experiment was safety-tested in February 2006