YDSE is carried with two thin sheets of thickness 10.4 mm each and refractive index ${\mu }_1$=1 52 . and ${\mu }_2$ =1.40 covering the slits S₁ and S₂ , respectively. If white light of range 400 nm to 780 nm is used, then which wavelength will form maxima exactly at point O, the centre of the screen.