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A monochromatic light is incident on a Youngs double spilt setup that has a slit seperation of 30um. the resultant bridge fringe seperation if 2.15cm on a 1.2 m from the double slit. what is the seperation 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 im lost on what there trying to get me to solve for ie.

**what is the seperation 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