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25.1 The Ray Aspect of Light
Light can travel from a source to another location in three different ways.
It can come directly from the source, such as from the Sun to Earth.
Light can travel through various media to the person.
Light can come from a mirror.
Light is modeled as traveling in straight lines.
Light may change direction when it encounters objects such as a mirror or when it passes from one material to another, but it continues in a straight line.
Light rays can be visualized as laser rays or even science fiction depictions of ray guns.
A straight line is what the word "ray" means.
Light can travel from a source to another location.
It can travel through media.
It can look like a mirror.
Light travels in straight lines when it interacts with large objects.
Experiments and our own experiences show that when light interacts with objects several times as large as its wavelength, it travels in straight lines and acts like a ray.
Its wave characteristics don't show up in those situations.
Since the wavelength of light is less than a thousandth of a millimeter, it acts like a ray in a lot of situations.
When light encounters a mirror, it acts like a ray, with only subtle wave characteristics, because we can't see it with our eyes.
Ray characteristics will be the focus of this chapter.
Since light moves in straight lines, changing directions when it interacts with materials, it is described by geometry and simple trigonometry.
Light changes direction when it interacts with matter.
For situations in which light bounces off matter and for situations in which light passes through matter, these are the laws of reflection and refraction.
Geometric optics deals with the ray aspect of light.
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