YDSE in Water

Q. In a double slit experiment when light of wavelength $400nm$ was used the angular width of the first minima formed on a screen placed $1m$ away was found to be $0.2°$. What will be the angular width of the first minima, if the entire experimental apparatus is immersed in water? (${\mu }_{water}$ = 4/3)

1. $0.266°$
2. $0.15°$
3. $0.05°$
4. $0.1°$

Q. Young's double slit experiment is performed using light of wave length $\lambda$. One of the slits is covered by a thin glass sheet of refractive index $\mu$ at this wavelength. The smallest thickness of the sheet to bring the adjacent minimum to the centre of the screen is

1. $\frac{\lambda }{2(\mu -1)}$
2. $\frac{\lambda }{(\mu -1)}$
3. $\frac{\lambda }{2\mu }$
4. $\frac{\lambda }{\mu }$

Q. Two sources are placed on x- axis at a separation $d=3\lambda$. An observer starts moving from A on a circular track of radius $R(R>>d)$. How many bright points and dark points will he observe? Find the angular positions of maxima and minima.

1. Total No. of bright spots and dark spots are 12.
2. Total No. of bright spots and dark spots are 3.
3. Angular position of maxima is $\frac{\pi r}{6}$.
4. Angular position of minima is $\frac{\pi r}{12}$.