Question

YDSE is carried with two thin sheets of thickness 10.4`mu` m each and refractive index `mu_1 = 1.52 and mu_2 = 1.40` covering the slits `S_1 and S_2` respectively. If white light of range 400nm to 780 nm is used, then which wavelength will form maxima exactly at point O, the centre of the screen


A. `416 nm` only
B. `624 nm` only
C. `416 nm` and `624nm` only
D. none of these

Answer 1

Path difference `=(mu_(2)-mu_(1))t=12480A^(@)`
For maxima
`nlambda=12480A^(@)`
`lambda_(1)=12480 A^(@)`,
`lambda_(2)=6240 A^(@)`,
`lambda_(3)=4160 A^(@)`,
`lambda_(4)=3120 A^(@)`,
`:.` Only `6240 A^(@)` & `4160 A^(@)` exist in the spectrum.