In Young's double slit experiment, the slits are 2 mm apart and are...

Given, ${λ}_{1} = 12000 Å$

and~${λ}_{2} = 10000 Å$

$D = 2cm$

$d = 2mm = 2 \times {10}^{- 3}m$

We have,~

$\dfrac{\lambda1}{\lambda2} = \dfrac{n2}{n1} = \dfrac{12000}{10000} = \dfrac{6}{5}$

as $X = \dfrac{{n}_{1}{λ}_{1}D}{d}$~ & \left({n}_{1} = 5\right)$</p><p>$= \dfrac{5 \times 12000 \times {10}^{- 10} \times 2}{2 \times {10}^{- 3}}$</p><p>$= 5 \times 1 . 2 \times {10}^{4} \times {10}^{- 10} \times {10}^{3} = 6mm$