What is interference of light?

Prove that the law of conservation of energy is obeyed during interference of light.

Derive an expression for fringe width in Young's double slit interference of light.

Define coherent sources of light, fringe width and interference of light. Show that the width of dark fringe is equal to the width of bright fringe in Young's double slit experiment.

Show that in Young's double slit experiment for interference of light, the widths of the bright and dark fringes are equal.