1.

The two slits are 1 mm apart from each other and illuminated with a light of wavelength 5 xx 10^(-7) m.If the distance of the screen is 1 m from the slits then the distance between third dark fringe andfifth bright fringe is

Answer»

`1.5 mm`
`0.75 mm`
`1.25 mm`
`0.625 mm`

Solution :Distance of `5^(TH)` BRIGHT fringe from central fringe,
`X_(5B) = (5lambdaD)/(d)`......(i)
Distance of `3^(rd)` DARK fringe from central fringe,
`X_(3D) = (( 2XX 3 - 1)lambdaD)/(2d) = 5/2 (lambdaD)/(d) ...(ii)`
From (i) and (ii) required distance
`X_(5B) - X_(3D) = (5 - 5/2)(lambdaD)/(d) = 5/2 XX (5 xx 10^(-7) xx 1)/(1 xx 10^(-3)) = 1.25 mm`


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