We represent light by a ray. Again,we know light which is emitted from the sun has all seven colors in them,hence again seven light rays. So doesn't it mean that that light is again composed of $7$ rays? Why do we represent it by a single ray then? I beg pardon if this doesn't make any sense but i am confused by light having colours whereas each of those colours are again light waves.
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So doesn't it mean that that light is again composed of 7 rays?
No. There is no such thing as a specific countable number of light rays.
When we are doing ray optics the rays that we draw do not represent certain amounts of light. The rays represent the geometry. They are drawn perpendicular to the wavefronts since that is the direction of wave propagation, but they do not represent a certain amplitude, frequency, or phase. They are useful for figuring out the geometry of wave propagation when diffraction is negligible.
Once you have figured out the geometry then you can relate things like the intensity or phase at some target to the properties of the source. And the same relationship will hold regardless of the strength or spectral characteristics of the source except as those influence the properties of the optical elements along the ray.
Dale
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