In Young's double slit experiment, separation between the slits is $2 × 10^{–3} m$ and distance of the screen from the slit is 2.5 m. Light in the range of 2000–8000 Å is allowed o fall on the slits. Wavelength in the visible region that will be present on the screen at $10^{–3} m$ from the central maxima will be

4000 Å

$δ=\frac{xd}{D}=\frac{10^{-3}×2×10^{-3}}{2.5}=8000Å$

For bright line = $n_1λ_1=n_2λ_2=n_3λ_3$

If $n_1=2⇒ λ_1= 4000Å$

i.e., second bright line for visible region is present.