Solution

Given,

The wavelength of light (λ) \(=6.2\times10^{-7}=6.2\times10^{-7}m\),
Distance between the slits and screen (D) = 80 cm = 0.8 m,
Separation of slits (d) =?,
Separation of four bright fringes (y) = 3β = \(2.5\times10^{-3}\) m

Here, \(\beta=\frac{\lambda D}d\) is the fringe width,

Now,

\(y=\beta=\frac{3\lambda D}d\)

Or, \(d=\frac{3\lambda D}y\)

Or, \(d=\frac{3\times6.2\times10^{-7}\times0.8}{2.5\times10^{-3}}\)

∴ d = 5.95 x 10^-4 m

Thus, the required distance is, d = 5.95 x 10^-4 m