1.

In Young's double slit experiment, using monochromatic light of wavelength lamda, the intensity of light at a point on the screen where path difference is lamda is K units. The intensity of light at a point where path difference is lamda/3 is

Answer»

4K
K
2K
`(K)/(4)`

Solution :(d): INTENSITY at any POINT on the screen is
`I = 4I_(0) cos^(2)(PHI)/2`
where `I_(0)` is the intensity of either wave and `phi` is the phase difference between two waves.
Phase difference, `phi = (2pi)/(lamda) xx` Path difference
When path difference is `lamda` then `phi = (2pi)/(lamda) xx lamda = 2pi`
`:. I = 4I_(0) cos^(2) ((2pi)/2) = 4I_(0) cos^(2) (pi) = 4I_(0) = K` ...(1)
When path difference is `(lamda)/3` , then
`phi = (2pi)/(lamda) xx (lamda)/3 = (2pi)/3`
`:. I = 4I_(0) cos^(2) ((2pi)/(3)) = K/4`[Using (i)]


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