Jack and Jill are sitting under an old wooden bridge one night while a street la

Question

Jack and Jill are sitting under an old wooden bridge one night while a street lamp with a wavelength of 600 nm shines through two small cracks in a board. They notice fringes of light on the ground 4.2 mm apart. If the board is 3.05 meters above the ground, what is the distance (in mm) between the cracks? You need not enter units, only the numerical portion of your answer.

Explanation / Answer

This is an application of the 2 slit interference formula. ym = location of the mth fringe on the screen= mR/d where m=0 is the central fringe, R = distance of screen from slits,d = slit separation, and we assume small angles (i.e., R >>d). fringe separation = y1 - y0 = R/d =(3.05)(6 x 10 -7)/d = .0042 from this you can find the slit separation d. hope this helps!

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