Why are parallel slits preferable to pinholes in Young's double slit experiment?

How will the angular separation and visibility of fringes in Young's double slit experiment change when Width of the source-slit is increased.

How would the angular separation of interfernece frings in Young's double slit experiment change when the distance of separation between the slits and the screen is doubled?

How will the angular separation and visibility of fringes in Young's double slit experiment change when screen is moved away from the plane of the slits.

Define the term'coherent sources' which are required to produce interference pattern in Young's double slit experiment.

What will be the effect on the fringes formed in Young's double slit experiment, if the apparatus is immersed in water,

Prove that the fringe width of both the brigth and dark fringes in interference is same in Young's double slit experiment.

If the separation between two alits is decreased in Young's double slit experiment,keeping the screen position fixed,what will happen to the fringe width?

What is the effect of slit width and wavelength of light source on fringe width of the fringes formed by Young's double slit experiment?