Young's Double-Slit Experiment question

[pre-med]

Homework Statement

With regard to Young's double slit experiment, locate the position above the central axis of the 3rd bright fringe for light of wavelength 500nm incident on slits separated by 0.1mm, when a thin (0.001mm) parallel sheet of glass of index 1.4 is placed in front of the slits. The distance from the slits to the screen is 2 meters.

Homework Equations

Where do I use the distance to the screen (the 2 meters)? Am I missing something or is it just useless information??

The Attempt at a Solution

a * sin($$\theta$$) = (m*$$\lambda$$) - (nd)
a=.0001m
m=3
$$\lambda$$=500nm
n=1.4
d=1*10^-6

$$\theta$$ = 0.001

 

[dlgoff]

They are wanting the position of the 3rd bright fringe from the center. So wouldn't you need to find an angle and use the distance from the slits to the screen to find this unknown distance?

 

[pre-med]

I got it... Thanks for the help.