1.

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

Answer»

`(7 lambda)/(12)`
`(15 lambda)/(4)`
`(lambda)/(2)`
`(3 lambda)/(4)`

Solution :Path difference at `S_(2)` is `2lambda`. So for minimum INTENSITY at P,
`S_(1)P -S_(2)P = (3lambda)/(2)`....(1)

or `sqrt(4LAMBDA^(2) + x^(2)) - x = (3 lambda)/(2)`
Then `x = (7lambda)/(12)`


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