Answer
0.19 mm apart
Work Step by Step
The spacing on the screen between bright fringes is addressed in Example 24-1.
For light shining through 2 slits separated by a distance d, the second order fringe on a screen a distance $\mathcal{l}$ away occurs at a distance of $\frac{2 \lambda \mathcal{l}}{d}$ from the centerline.
The distance between the second order fringes created by two different wavelengths is $\frac{2 \Delta \lambda \mathcal{l}}{d}$.
$$=\frac{2 ((720-660)\times10^{-9}m) (1.0m)}{ 0.62\times10^{-3}m }$$
$$=1.9\times10^{-4}m $$
