How Do You Calculate the Fringe Separation in Young's Double Slit Experiment?

[Dx]

Hello,

A monochromatic light is incident on a Youngs double spilt setup that has a slit separation of 30um. the resultant bridge fringe separation if 2.15cm on a 1.2 m from the double slit. what is the separation between the 3rd order bright fringe and the 0th order bright fringe?

I know that d=30um, L=1.2m and m=0, 3 orders. ao using x_1=L[the]_1 = 1.2(?)=2.15 = 17.92
I think I am lost on what there trying to get me to solve for ie. what is the separation between the 3rd order bright fringe and the 0th order bright fringe? what do they mean? I have this formula sin[the]= m[lamb] /d. How do i solve for it, i must be close, right?
Plz help?
Dx

 

[quantumdude]

Originally posted by Dx
I think I am lost on what there trying to get me to solve for ie. what is the separation between the 3rd order bright fringe and the 0th order bright fringe? what do they mean?

They mean, "How far apart on the screen are those two fringes?"

I have this formula sin[the]= m[lamb] /d.

OK, now use geometry. Draw the setup, and you will have a triangle with one angle θ and the unknown distance opposite that angle.

 

[Dx]

Thats it tom.
You make it too easy, i got 8.60cm as my answer. is that correct?
Thanks!
Dx