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Figure shows two, identical narow slits S_(1) and S_(2). A very small completely strip is placed at distacne y from the point C. C is the point on the screen equidistant from S_(1) and S_(2). Assume lamda lt lt d lt lt D, where lamda, d and D have usual meaning. When S_(2) is covered the force due to light acting on strip is f and when both slits are opened the force acting on strip is 2f. Find the minimum positive y(lt lt D) coordinate (in cm) of the strip if (lamdaD)/d=4cm |
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Answer» When waves due to both the sources superpose at `P`,the net intensity at `P` is `I=4I_(0)"COS"^(2) (piy)/(beta)`, where `beta=(lamdaD)/d` Since FORCE on strip at `P` is twice due to individual source Hence `I=2I_(0)` `:."cos"^(2) (piy)/2=1/2` or `(piy)/(beta)=(PI)/4` or `y=(beta)/4=(lamda D)/(4d)` 
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