The two slits are 1 mm apart from each other and illuminated with a light of wavelength `5xx10^(-7)` m. If the distance of the screen is 1 m from the slits, then the distance between third dark fringe and fifth bright fringe is

Options

A. `1.5mm`
B. `0.75mm`
C. `1.25mm`
D. `0.625 mm`

Answer

C

Explanation

Distance of 5th bright fringe from central fringe
`x_(5D)=(5lambdaD)/d`
Distance of 3rd dark fringe from central fringe
`x_(3D)=((2xx3-1)xxD)/(2d)=(5lambdaD)/(2d)`
Required distance,
`x_(5D)-x_(3D)=(5-5/2)(lambdaD)/2=5/2xx(5xx10^(-7)xx1)/(1xx10^(-3))=1.25mm`