What is not an essential condition for an observable interference pattern to occur between the waves of two sources?
A) the frequencies of two sources are equal
B) source must be coherent
C) source must emit equal amplitude waves
D) the waves from sources must overlap

Hint: When two waves interfere, there are two conditions they must satisfy to interfere constructively or destructively. They need to have a constant phase difference and they must have the same wavelength. If anyone of the options is other than these two, they aren’t necessary for interference to occur.

Complete step by step answer:
When two waves come together, they can interfere constructively or destructively. To set a stable and clear interference pattern, two conditions must be satisfied, they are, the sources from which waves are coming must be coherent. Coherent waves means they will have constant phase difference. Next condition is the source from which the wave is propagating must be monochromatic, all the waves will be having the same wavelength.
If we take the third option, the amplitude must be the same for two waves is not a required condition for waves to interfere constructively or destructively.

So, the correct answer is “Option C”.

Additional Information: When two waves combine or intersect their paths, they either add up or differ each other according to the phase differences resulting in a single wave finally. If two waves superpose to form a resultant wave that is greater, lower or same as the amplitude of the initial wave, it is called interference. Constructive or destructive interference results when coherent waves interact with each other.

Note: If the crest of one wave meets the crest of another wave, the interference is called constructive interference. If the crest of one wave meets the trough of another wave, it results in destructive interference. The net amplitude adds up in the first case and is equal to the difference of both waves in the second case.