JEE MAIN - Physics (2003 - No. 21)
To demonstrate the phenomenon of interference, we require two sources which emit radiation
of nearly the same frequency
of the same frequency
of different wavelengths
of the same frequency and having a definite phase relationship
Explication
To observe the phenomenon of interference, you need two sources that emit radiation of the same frequency and have a definite phase relationship. This is because interference is a result of the superposition of waves, which requires the waves to be coherent. Coherence is achieved when the waves have a constant phase difference, which implies that they are of the same frequency and have a definite phase relationship (a phase relationship that does not change with time).
So, the correct answer is :
Option D : of the same frequency and having a definite phase relationship.