1.

A parallel beam of light of wavelength lambda is incident normally on a single slit of width d. Diffraction bands are obtained on a screen placed at a distance D from the slit. The second dark band from the central bright band will be at a distance given by ....

Answer»

`(2lambdaD)/(d)`
`lambda dD`
`(lambdaD)/(2d)`
`(2lambdad)/(D)`

Solution :For diffraction condition for dark fringe `d SIN theta_(N)=n lambda`
But for smaller angle `sin theta_(n)=(x_(n))/(D)`
`:. In (dx_(n))/(D)=n lambda, n=2`
`:.x_(2)=(2lambdaD)/(d)`


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