Answer:
n = 3
Step-by-step explanation:
We know that the nth-order maximum for the Young's two-slit experiment is given by the following expression:
dsin(θ) = nλ
If two maxima concides we must have the relation:
nλ1 = mλ2 --- eq1
In this particular experiment
m = n+1
λ1 = 680 nm
λ2 = 510 nm
Replacing m in eq1 we have
nλ1 = (n+1)λ2
Solving for n we have:
n = λ2/(λ1-λ2)
Therefore:
n = 510/(680-510)=3