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Homework Help: DVD/CD track spacing and storage capacity

  1. May 5, 2014 #1

    I finished an experiment of finding out the track spacing of a CD and a DVD.
    My laser wavelength was 654nm which I used to calculate track spacing of the optical discs.

    I got a track spacing of a CD 1.57um which is close to a real value of 1.6um,
    and the track spacing of a DVD 0.72um which is close to a real value of 0.74um.

    Then I calculated the storage capacity of both and got 654 Megabytes for a CD which is pretty good but only 2786 MB for a DVD, which is pretty far from its true value of 4700 MB.

    What did I do wrong?

    Oh here's the worksheet I used to calculate the storage capacity:
    http://www.teachengineering.org/collection/uoh_/activities/uoh_diffraction/uoh_diffraction_activity1_worksheet_mhf_tedl.pdf [Broken]


    Last edited by a moderator: May 6, 2017
  2. jcsd
  3. May 5, 2014 #2


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    Staff: Mentor

    Please show your work.
  4. May 5, 2014 #3
    This is my second experiment where I got similar data as one mentioned in my first post.

    Attached Files:

  5. May 5, 2014 #4
    Not all DVD's store 4.7 G bytes. Some DVD-RAM store 2.5 G bytes. May be that's what you used?
  6. May 5, 2014 #5
    But as far as I know all DVD types have the same track spacing?

    As well, I measured the track spacing similar to a normal DVD, and still got 2.8GB...
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