Explain why you don’t need a displacement vs. distance graph for light, but you do for other traveling waves.

Answer 1

Do you graph displacement versus distance for a traveling sound wave?
If it is a wave on a string, the actual displacement motion is sideways to the direction of travel and it makes sense to graph it as a function of time. In the case of light there is no motion sideways, although in fact you can graph the electric and magnetic fields perpendicular to the direction of the light ray.