Question

In YDSE, both slits are covered by transparent slab. Upper slit is covered by slab of refractive index $1.5$ and thickness $t$ and lower is covered by refractive index $\frac{4}{3}$ and thickness $2t$, then central maxima

• A. shifts in $+ve$ $y-$axis direction.
• B. shifts in $-ve$ $y-$axis direction.
• C. remains at same position.
• D. may shift in upward or downward depending upon wavelength of light.

Answer 1

The correct option is B shifts in $-ve$ $y-$axis direction.


For upper slit, path difference is given by
$\Delta x_1=({\mu }_1-1)t=(1.5-1)t=0.5t$
For lower slit, path difference is given by
$\Delta x_2=({\mu }_2-1)t=(\frac{4}{3}-1)2t=\frac{2}{3}t$
As $\Delta x_2>\Delta x_1$, so, shift will be along $-ve$ $y-$axis direction.