Diffraction Grating
Light, Sound and Waves

A CD or gramophone record as a grating

Practical Activity for 14-16 PRACTICAL PHYISCS


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


  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

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