In my collection of computer disks are several that I cannot tell if they are CD

Question

In my collection of computer disks are several that I cannot tell if they are CD regular DVD or Blu-ray DVD discs. It was suggested I can use my laser pointer to determine which is which.Since the discs consists of closely spaced metallized grooves a multi slit diffraction pattern characteristics of the groove space and should be created. The amount of information stored increases going from CDs to DVDs to Blu-ray DVD and hence I expect the groove spacing it to be largest on CD and smallest on the Bluray with the regular DVD somewhere between.

B) A DVD disc replaces the CD and _1 is measured to be 46.0=0.80 radians. What is the spacing between tracks on DVD? What is _2?

Explanation / Answer

using the diffraction condtion           m = d sin          d = m / sin given   = 534nm , = 46 and m = 1        d = 534x10^-9 / sin 46           = 0.7423x10^-6 m           = 0.7423m for 2 ,      2 =sin^-1 [ 2 (534x10^-9) / 0.7423x10^-6 ]           = impossible           

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