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Activity (Hands-On)Grades 11 - 12

Estimating the Storage Capacity of a CD/DVD

Photo shows green laser light being diffracted on a CD. There are six labels indicated on the setup (A-F). A DVD (A) and CD (B) are taped to the edge of the table. A protractor (C) is placed on top of a white sheet of paper (E). Spacers (D) are placed between the protractor and white sheet of paper. The laser beam (F) is aligned with the 90 degree mark of the protractor.Figure 1: Experimental setup.

Students estimate the storage capacity of CDs and DVDs by assessing diffraction patterns of green and red laser beams.

Optical science engineers and materials science engineers design and create devices that satisfy the ever increasing demand for digital storage. The advancement from CDs to DVDs allows more storage per disk but also provides challenges for engineers because the physical structures ("pits") that store data on the disks become smaller and the CD/DVD players' lasers operate at the diffraction limit (resolution) of light.

After this activity, students should be able to:

  • Describe how a CD or DVD stores information.
  • Explain that the laser's wavelength limits how small the pits on a CD or DVD can be.
  • Explain why a Blu-ray disc can store more information than a CD or DVD.

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