Welcome to practical physicsPracticle physics - practical activities designed for use in the classroom with 11 to 19 year olds

A CD (or gramophone record) as a grating


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



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


Related experiments

Coarse diffraction grating

Measuring the wavelength of light


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