A small transparent slab containing material of μ =1.5 is placed along AS2 (Fig.10.6). What will be the distance from O of the principal maxima and of the first minima on either side of the principal maxima obtained in the absence of the glass slab.
AC = CO = D, S1C = S2C = d << D
Whenever a transparent slab of refractive index μ and thickness t is inserted in the path of the ray the fringes on the screen shifts by (μ-1) t towards the slab.
Given AC = CO = D, S1C = S2C = d << D
L=d/4, μ=1.5
∴ the optical path difference is given by
For principal maxima OPD=0, i.e.
The distance from O to principal maxima is,
The path difference for first minima is ± (λ/2)
i.e.
Since diffraction occurs when slit width is equals to the wavelength i.e. λ =d
Considering the positive side,
Considering the negative side,
The distance of first principal minima from O on the positive side is,
The distance of first principal minima from O on the negative side is,