Two slits at a distance of `1mm` are illuminated by a light of wavelength `6.5xx10^-7m`. The interference fringes are observed on a screen placed at a distance of `1m`. The distance between third dark fringe and fifth bright fringe will be

Options

A. `0.65 mm`
B. `1.63 mm`
C. `3.25 mm`
D. `4.88 mm`

Answer

B

Explanation

`d=1 mm, lambda=6.5xx10^(-7)m, D=1 m`
Third dark fringe `y_(3)^(')=(2xx2+1)(Dlambda)/(2d)=(5Dlambda)/(2d)`
Fifth bright fringe `y_(5)=(5Dlambda)/d`
`y_(5)-y_(3)^(')=(5Dlambda)/(2d)=5/2xx(1xx6.5xx10^(-7))/(1xx10^(-3))`
`=16.3xx10^(-4)m`
`=1.63 mm`