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Question
Discuss the special cases on first minimum in Fraunhofer diffraction.
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Solution
- Divide the slit AB into two halts AC and CB.
- Two different points on the slit which are separated by the same width is corresponding points.
- The path difference of light waves from corresponding points meet at p and interfere destructive to make the first minimum.
δ = `"a"/2` sin θ
The condition for p to first minimum
`"a"/2 sin θ = lambda/2`
a sin θ = λ (first minimum)
a sin θ = 2 λ (second minimum)
a sin θ = 3 λ (third minimum)
`("a" sin theta)/(2"n") = lambda/2`(nth minimum)
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