Question

In a two-slit experiment using coherent light, the distance between the slits and the screen is 1.10 m, and the distance between the slits is 0.0400 mm. If the second order bright fringe is measured to be 4.20 cm from the centerline on the screen, what is the wavelength of light?

Answer 1

2-slit pattern, slit spacing d, mth bright fringe: sinθ m = mλ d

Fringe position on screen at distance L: ym = L tanθ m ≅ L m( ) λ d

ym = 1.10m( ) 2λ 0.000040m → λ = ( ) 0.042m

0.000040m / 2⎡ ⋅( ) 1.10m ⎣ ⎤⎦ = 7.63×10−7 m

NOTE:tan and sin will be small angles