Using a wavelength laser, you form the diffraction pattern of a wide slit on a screen. you measure on the screen that the dark fringe is away from the center of the central maximum. how far is the screen located from the slit?

y = λ   L/ a

Explanation:

The diffraction pattern of a single slit is side for the case of destructive interference by

     a sin  θ = m λ

Where a is the width of the slit, lm the wavelength and m an integer

In general the screen is much larger than the width of the spectrum, so the sine can approach the tangent

       sin  θ = tan θ = y / L

Substituting remains

       a y / L = m λ  

       y = m λ  L /a

For the first dark strip m = 1

      y = λ   L/ a

explanation:

wheres the pic