Answer the following with reference to the phenomenon of interference of light.
(a) State the principle of superposition of waves.
(b) Define coherent sources of light.
(c) Write the two essential conditions that must be satisfied by two light sources to produce a sustained, observable interference pattern.
(d) For interference fringes formed on a distant screen, state in symbolic form the condition for (i) constructive and (ii) destructive interference in terms of the path difference Δx.