A ray is a simple model of light's direction. In this model light travels in straight lines until it meets a surface.
Example
A ray is a simple model of light's direction. In this model light travels in straight lines until it meets a surface. Exact arithmetic here means exact results for the stated model inputs; measured inputs still carry uncertainty and significant-figure limits.
highlighted = computed this step
A ray is a direction model
A ray is not a tiny object flying through space. It is a line we draw to track the direction light travels. When the setup is much larger than the wavelength, this straight-line model is useful.
ray⇒direction of light
In one medium the ray stays straight
In a uniform medium, the ray keeps going in the same direction until it meets a surface. That is why the ray model uses straight lines to track where light goes.
same medium⇒straight ray
Several rays can model one beam
A ray diagram can use more than one line for the same light beam. Those lines are bookkeeping directions; they are not separate little particles of light.
ray bundle⇒several tracked directions
opticsRays are not tiny sticks of light. They are a geometry model for direction, useful when wavelength effects are too small to matter.