Answer:
λ = 470.66 nm
Explanation:
for bright fringe[tex]y_m = \frac{m\lambda D}{d}[/tex]
D= distance between slit and screen
d= distance between the slits
for first order bright fringe m = 1,
[tex] y_1 = \frac{1\lambda D}{d}[/tex]
[tex]y_1 = {706*D}{d}[/tex]
for dark fringe,we have
[tex]y_m = {(m + 1/2)\lambda D}{d}[/tex]
Now to get the dark fringes at the same location we should have;
(706)D/d = (m + 1/2)λD/d
put m = 1
(1 + 1/2)λ = (706)
λ = 470.66 nm