Assertion : Beats can also be observed by two light sources as in sound.Reason : Light sources have constant phase deference.

The assertion and reason given are not entirely correct.

Beats are a phenomenon that occur in waves when two waves of slightly different frequencies interfere with each other. This is commonly observed in sound waves, where it is perceived as a variation in loudness. However, this phenomenon is not typically observed in light due to the high frequency of light waves.

The reason given, "Light sources have constant phase difference", is not entirely accurate. While it is true that coherent light sources (such as those produced by a laser) have a constant phase difference, this is not a characteristic of all light sources. Furthermore, even with a constant phase difference, beats would not be observed in light due to the aforementioned high frequency of light waves.

In conclusion, while beats are a common phenomenon in sound waves, they are not typically observed in light waves, regardless of whether the light sources have a constant phase difference or not.