Question

Two coherent sources are placed 1mm apart and generate
interference fringes on a screen 0.9 m away. The second dark
fringe is formed at a distance of 0.9mm from the central fringe.
Determine the wavelength of the monochromatic light used.

Answer 1

hi

here d(distance bw 2 coherent sources ) =1mm

D(dist. bw screen n source)=0.9m

second dark band means

"y=3×D×ambda/2d"

using this formula find lambda where y=0.9mm