A CD or gramophone record as a grating
Practical Activity for 14-16
Students observe the spectrum produced when light falls obliquely on a CD.
Apparatus and Materials
CD or gramophone record
Health & Safety and Technical Notes
- 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.
This experiment was safety-tested in February 2006