A beam of light consisting of two wavelengths, 650 nm and 520 nm, is used to obtained interference friges ina Young's double slit experiment.
a. Find the distance of the third bright fringe on the screen from the central maximum for wavelength 650 nm.

Explanation

a. `lamda=650xx10^(-9)m, d=2xx10^(-3)m, D=1.2mm, n=3`
`:.y_(3)=(n lamda D)/d=(3xx650xx10^(-9)xx1.2)/(2xx10^(-3))=1.17xx10^(-3)m`
`beta=(D lamda)/d=(y_(n))/n=(1.17xx10^(-3))/3=0.39xx10^(-3)m`
b. `(nDlamda_(1))/d=((n+1)Dlamda_(2))/d` (higher order of lower wavelength coincides with lower order of higher wavelength)
`n lamda_(1)=(n+1)lamda_(2), n/(n+1)= (lamda_(2))/(lamda_(1))=520/650=0.8`
`n=0.8n+0.8, 2n=0.8 :. n=4`
`y_(n)^(.)=(n D lamda_(1))/d=n beta=4xx0.39xx10^(-3)=1.56xx10^(-3)m`