optics: Information in a CD is stored in “pits” whose depth is 1/4 wavelength...?
Information in a compact disc is stored in “pits”
whose depth is essentially one-fourth of the
wavelength of the laser light used to “read” the
information. That wavelength is 780 nm in air, but
the wavelength on which the pit depth is based is
measured in the n = 1:55 plastic that makes up
most of the disc. Find the pit depth.
i know n=c/v...but not sure how to plug this in...
Update:c= speed of light thru air
v= speed of light thru a medium
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first calculate the wavelength in the plastic (it is different to one in air)
That will be L/n=780nm/1.55. The pit height is 1/4 of it = 125.8 nm
The formulae:
Lambda=2*pi*c/omega. Because omega doesn't change when passing through media Lambda is proportional to the speed of light in that media. So, if c in plastic is 1.55 times less then so is the wavelength.