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whatisreality
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Homework Statement
A ray travels as shown in the image attached below. In this case, Fermat's principle may be written as
##A =\frac{n(1+ay)}{\sqrt{1+(y')^2}}##
Where y' is dy/dx, n is the index of refraction and A is a real constant.
The trajectory of a ray of light is given by
##y = -\frac{1}{a}## ## + \frac{A}{na}## ##\cosh{\frac{na}{A}(x-x0)}##
When the ray is observed from a height y above the x axis, it seems to come from the ground at horizontal distance d from the observer (see figure). Determine d if a(x−x0) is small. Write your answer in terms of y and a.
Homework Equations
The Attempt at a Solution
I've tried to work out the specific trajectory for the ray that grazes the x-axis at xg. For x=xg, dy/dx is 0 and y=0, so at that point A = n. Although there is a sqrt involved, take positive n because n=c/v is always positive as far as I know.
Sub that into the second equation for y, taking y=0 again, then I got xg = x0.
So the specific trajectory of this ray would then be
##y = -\frac{1}{a}## ## + \frac{1}{a}## ##\cosh{a(x-xg)}##
Really have no clue what to do from there! I did try finding the tangent to the curve to maybe find an expression for the length of the hypotenuse, but that didn't work. So I don't know.