- #1
Feodalherren
- 605
- 6
Homework Statement
In a Young’s double-slit experiment using light of wavelength
λ, a thin piece of Plexiglas having index of refraction
n covers one of the slits. If the center point on the
screen is a dark spot instead of a bright spot, what is the
minimum thickness of the Plexiglas?
Homework Equations
The Attempt at a Solution
If the center is to be a dark spot then the Plexiglas must delay the light by 1/2 λ.
Call the distance from each slit to the center d.
Call the thickness of the glass t.
Therefore
[itex]\frac{d}{\lambda} - (\frac{t}{\lambda/n} + \frac{d-t}{\lambda}) = \frac{1}{2}[/itex]
My reasoning is that this must be true because there is an extra wavelength in one of the paths. The book, however, reverses it. It takes what I have inside the parenthesis and subtracts that from d/λ. Other than that we agree. Why does the book reverse it?