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songoku
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Homework Statement
Two flat glass plates are stacked and a thin paper strip is inserted between them at one side, creating a narrow wedge-shaped space between the plates. As shown in the figure below, monochromatic light that has a wavelength in air is directed at the plates from above. When viewed from above, parallel bright and dark fringes appear. This is the result of interference between light reflected from the bottom surface of the upper plate and light reflected from the top surface of lower plate.
When the angle between the glass plates is θ, N number of bright fringes are observed between points P and Q, whose distances from O, the point of contact between the plates, are x1 and x2 respectively. What is the value of λ? (N is sufficiently large and θ is sufficiently small to that tan θ= θ
a. (x2 - x1)θ / N
b. 2(x2 - x1)θ / N
c. (x2 - x1)/ Nθ
d. 2(x2 - x1)/ Nθ
Homework Equations
d sin θ= nλ
d y / D = nλ
w = λD/d
The Attempt at a Solution
Actually I don't really understand the question. I think the interference pattern occurs at the bottom surface of the upper plate, not at PQ because the light reflected at the bottom part of the upper plate never reaches PQ, so the light reflected by both surfaces will superimpose each other at the bottom surface of the upper plate.
I don't know how to use all the formulas I wrote above for this question. I don't have d, D, w. I even don't know how to use the distance of PQ, angle, and N given by the questions because in my opinion they can't be put in the equation