A plane monochromatic light wave is incident on a double slit as illustrated in Figure 37.1. (i) As the viewing screen is moved away from the double slit, what happens to the separation between the interference fringes on the screen?
(a) It increases,
(b) It decreases,
(c) It remains the same,
(d) It may increase or decrease, depending on the wavelength of the light.
(e) More information is required,
(ii) As the slit separation increases, what happens to the separation between the interference fringes on the screen? Select from the same choices.

Explanation:

The separation between the interference fringes on the screen increases because the distance of the screen from the slit is increased. Therefore option (a) is  correct.

The separation between the interference fringes on the screen increases because  the distance of the screen from the slit is increased, which is contradictory. Therefore option (b) is incorrect.

The separation between the interference fringes on the screen increases because  the distance of the screen from the slit is increased, which is contradictory. Therefore option (c) is incorrect.

The separation between the interference fringes on the screen increases because  the distance of the screen from the slit is increased, which is contradictory. Therefore option (d) is incorrect.

The separation between the interference fringes on the screen increases because  the distance of the screen from the slit is increased, which is contradictory. Therefore option (e) is incorrect.

where are the vectors ?