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Light waves from two coherent source arr...

Light waves from two coherent source arrive at two points on a screen with path difference `0 and lambda//2`. Find the ratio of intensities at the points.

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Let `I_(1) = I_(2) = I_(0)`
(i) path diff. `= 0`, phase difference `phi = 0`
`:. I_(R) = I_(1) + I_(2) + 2sqrt(I_(1)I_(2)) cos phi`
`= I_(0) + I_(0) + 2 I_(0) cos 0^(@) = 4 I_(0)`
(ii) path diff. `lambda//2`, phase difference `phi' = (2pi)/(2) = pi`
`:. I_(R )' = I_(1) + I_(2) + 2sqrt(I_(1)I_(2)) cos phi`
`(I_(R ))/(I_(R')) = ( 4I_(0))/("Zero")` = infinite
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