(a) Write the conditions under which light sources canbe said to be coherent.(b) Why is it necessary to have coherent sources inorder to produce an interference pattern?

(a) Light sources can be said to be coherent under the following conditions:

1. The light sources must have the same frequency or wavelength. This is because coherence is the property of waves that enables them to interfere with each other. If the waves have different frequencies, they will not interfere constructively or destructively in a predictable manner.

2. The phase difference between the light sources must be constant. This means that the peaks and troughs of the waves from the two sources must align with each other at all times. If the phase difference is not constant, the interference pattern will not be stable.

(b) Coherent sources are necessary to produce an interference pattern because interference is the result of the superposition of two or more waves. If the sources are not coherent, the phase difference between the waves will not be constant, and the resulting pattern will be random and unpredictable. On the other hand, if the sources are coherent, the phase difference is constant, and the waves will always interfere in the same way, producing a stable and predictable interference pattern.