Angular width is related to the slit spacing (d) as:

θ = λ/d

Thus,

d = λ/θ

Where,

λ is the wavelength of light

θ is the angular width of the fringe on the screen

d is the spacing between the two slits.

Given,

Wavelength of light, λ = 600 nm = 600 × 10 ^{- 9} m

The angular width of the fringe θ = 0.1^°

Note: The given angular width is in degrees, We must convert degrees into radiant for the angular width of the fringe.

Thus, Angular width, θ of the fringe can be written in radians as

⇒

d =

⇒ d = 3.44 × 10 ^{- 4} m

The spacing between the two slits “d” is 3.44 × 10 ^{- 4} m