The fringe separation (β) in Young's double-slit experiment is calculated using the formula:
$\beta = \frac{\lambda D}{d}$
Here,
λ denotes the wavelength of the light.
D represents the distance from the slits to the screen.
d signifies the separation between the slits.
Provided values:
λ = 600 × 10-9 m; D = 1 m; d = 1.5 mm, which is equivalent to 1.5 × 10-3 m.
The fringe separation is calculated as follows:
$\beta = \frac{(600 \times 10^{-9} \text{ m})(1 \text{ m})}{1.5 \times 10^{-3} \text{ m}} = 4 \times 10^{-4} \text{ m}$