Constructive wave interference problem

  • Thread starter throllen
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  • #1
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Homework Statement



A sheet of glass is coated with a 505nm thick layer of oil (n = 1.42).

For what visible wavelengths of light do the reflected waves interfere constructively/destructively?

Homework Equations



For constructive interference

lamba=2nd/m

For destructive interference

lamba=2nd/(m-1/2)

The Attempt at a Solution



for constructive

2*1.42*505/(3 or 4) (since m=3 and 4 will give me a visible wavelength) lamba = 717 nm, 478 nm

for destructive

2*1.142*505/(3 or 4 + 1/2) (since m=3 and 4 will also give me a visible wavelength) lamba = 574, 410 nm

HOWEVER, they are wrong... so im completely clueless of what to do next.. help please >.<
 

Answers and Replies

  • #2
Doc Al
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A sheet of glass is coated with a 505nm thick layer of oil (n = 1.42).
Hint: How does the index of refraction of the oil compare to that of the glass. Does it matter?
 
  • #3
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glass is supposed to have a higher index of refraction.. yes it matters...
 
  • #4
Doc Al
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Hmmm... in that case your solution looks fine to me.
 

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