Answer:
When the sound waves modulate a beam of light, the sound track, which may be of variable density or of variable width, is a photographic record of the varying light.
Step-by-step explanation:
In motion-picture technology, the sound track ,narrow band, usually along the margin of the film, that carries the photographic or magnetic sound record. For sound reproduction, a beam of light is passed through the sound track onto a photocell connected, through an amplifier, to a loudspeaker. This optical system is the basic plan of sound reproduction in sound motion pictures. In stereophonic sound recording, a number of such bands may be used on the same film.
The Sun is a natural source for visible light waves and we can see the reflection of this sunlight off the objects around us. The color of an object that we see is the color of light reflected. All other colors are absorbed. Light bulbs are another source of visible light waves.