What is effect on the interference fringes in a Young's double slit experiment due to each of the following operations :
(a) the screen is moved away from the plane of the slits,
(b) the monochromatic source is replaced by another monochromatic source of shorter wavelength,
(c ) the separation between the two slits is increased,
(d) the source slit is moved closer to the double slit plane,
(e) the width of the source slit is increased.
(f) the width of two slits are increased,
(g) the monochromatic source is replaced by a source of white light ?
(In each operation, take all parameters, other than the one specified, to remain unchanged) NCERT Solved Example

Explanation

a. The distance between fringes is directly proportional to the distance between slits and screen (D). Thus the fringe separation increases but the angular separation remains constant.
b. Both fringe separation and angular separation of the interference pattern decrease with the decrease in wavelength.
c. Both fringe separation and angular separation of the interference pattern decrease with the increase in separation between slits.
d. For an interference pattern, it is required that `s/S < lambda/d`, where s is the size of the source, S is the distance between source and two slits and d is the distance between both the slits. As the slit source is moved towards the double-slit plane, S will decrease and the pattern will become more cumbersome till the time when no interference pattern will be observed when slits are too closer to the source.
e. Again as the slit width(S) is increased, the interference pattern becomes cumbersome, and with further increase in distance, there is no interference pattern observed.