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

Options

A. 416 nm only
B. 624 nm only
C. 416 nm and 624 bn only
D. None of these

Answer

c

Explanation

Path difference `= (mu_(2) - mu_(1))t = 12480 Å`
For maxima,
`n lambda = 12480 Å`
`lambda_(1) = 12480 Å`
`lambda_(2) = 6240 Å`
`lambda_(3) = 4160 Å`
`lambda_(4) = 3120 Å`
Therefore, only `6240 Å` and `4160 Å` exist in the spectrum.