Two coherent point sources `S_1 " and "S_2` vibrating in phase light of wavelength `lambda`. The separation between the sources is `2lambda`. The smallest distance from `S_(2)` on a line passing through `S_2` and perpendicular to `s_(1)s_(2)` where a minimum of intensity occurs is

Explanation

Path difference at `s_(2)" is "2lambda`. Therefore for minimum intensity at P let x be the minimum distance from `s_(2)`. Then
`s_(1)P-s_(2)P= (3lambda)/(2) ne (lambda)/(2)"………"(1)`
or `sqrt(4lambda^(2)+ x^(2))-x= (3lambda)/(2)`
Solving this equation we get `x= (7lambda)/(12)`
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