1. If an observer receives 'sound waves' form two sources whose frequencies differ slightly, he may detect periodic rises and falls in the intensity known as 'beats'. Explain, with the aid of diagrams or graphs, what is meant by the terms 'sound waves' and 'beats'.
2. Light from two monochromatic sources whose wavelengths differ slightly is shone onto a screen. Discuss whether 'optical beats' ( i.e. a phenomenon identical to beats in sound) can be observed.
[ From New Way Physics for Advanced Level Wave Motion (Book2) ]