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Double-Slit Experiment problem?

  • Thread starter brinstar
  • Start date
  • #1
62
1

Homework Statement


In a double-slit experiment, the third order bright fringe is 15 mm from the central fringe. What is the distance of the first (zero-th order) dark fringe from the central maximum?

Homework Equations


(m+.5)(lambda) = dsin(theta) => dark fringe
m(lambda) = dsin(theta) => bright fringe

The Attempt at a Solution


I honestly don't know. Like, there's no angle or wavelength. The most I've come up with is 15 mm divided by 3 (because it's the third) and getting 5 mm. I seriously don't know.
 

Answers and Replies

  • #2
413
72
the equation you need is
dsinθ = nλ for maxima....you have this in your post
 
  • #3
62
1
the equation you need is
dsinθ = nλ for maxima....you have this in your post
But where do I get the angle and wavelength from?
 
  • #4
264
26
For angles this small you can use the approximation: sin theta = theta = x / D where x
is the fringe displacement from the central maximum and D is the distance to the screen.
 

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