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jegues
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Homework Statement
When a 450-nm light is incident normally on a certain double-slit system, the number of interference maxima within the central diffraction maxima is 5. When 900-nm light is incident on the same slit system, the number of interference maxima within the central diffraction maxima is ______?
Homework Equations
The Attempt at a Solution
The answer is given as 5, but I can't figure out why.
[tex]dsin\theta = m \lambda[/tex]
[tex]dsin\theta = n \lambda^{'}[/tex]
Since dsin(theta) shouldn't change,
n = (m/2)
If we have 5 bright fringes in our central envelope, m = 2, therefore n=1.
So the number of bright fringes in the new central envelope is 2n+1 = 3 which is incorrect.
What am I misunderstanding?