What are coherent sources? Why two independent sources of light of the same wavelength cannot produce interference fringes ? Explain.

Ans 1. Two light sources are said to be coherent if the waves emitted from them have same phase and same frequency. For example:- Laser light produce coherence.

Interference is possible when:

1. The both light should have same wavelength.

2. They should have a constant path(which in turn causes phase) difference, same frequency.

3. They should be coherent.

Here two independent sources do not produce interference because the phase difference between two light waves emitting from two independent sources is not constant due to which at the particular point interference pattern changes reflectively and due to low sensitivity of our eyes no observable interference pattern is obtained.