Explain interference of light? Write two essential conditions for sustained interference pattern to be produced on the screen.

Illustrate a graph showing the variation of intensity versus the position on the screen in Young's experiment when (a) both the slits are opened and (b) one of the slits is closed.

What is the effect on the interference pattern in Young's double slit experiment when:

(i) Screen is moved closer to the plane of slits?

(ii) Separation among two slits is enhanced. Explain your answer in each case.