Question

What are coherent sources? Why are they necessary for observing a sustained interference pattern?

Hint:

Laser light is an example of a coherent source, which is why it is commonly used in interference experiments.

Answer 1

Definition of Coherent Sources: Coherent sources are two or more sources of light that emit waves with a constant phase difference and the same frequency. Importance for Interference:
For a sustained interference pattern:
The phase difference between the waves must remain constant over time.
If the sources are incoherent, the phase difference changes randomly, leading to the destruction of the interference pattern. Thus, coherent sources are essential to produce stable and visible interference fringes.