Page 1128 - College Physics For AP Courses

1116 Chapter 25 | Geometric Optics
Big Idea 6 Waves can transfer energy and momentum from one location to another without the permanent transfer of mass and serve as a mathematical model for the description of other phenomena.
Enduring Understanding 6.E The direction of propagation of a wave such as light may be changed when the wave encounters an interface between two media.
Essential Knowledge 6.E.1 When light travels from one medium to another, some of the light is transmitted, some is reflected, and some is absorbed. (Qualitative understanding only.)
Essential Knowledge 6.E.2 When light hits a smooth reflecting surface at an angle, it reflects at the same angle on the other side of the line perpendicular to the surface (specular reflection); and this law of reflection accounts for the size and location of images seen in plane mirrors.
Essential Knowledge 6.E.3 When light travels across a boundary from one transparent material to another, the speed of propagation changes. At a non–normal incident angle, the path of the light ray bends closer to the perpendicular in the optically slower substance. This is called refraction.
Essential Knowledge 6.E.4 The reflection of light from surfaces can be used to form images.
Essential Knowledge 6.E.5 The refraction of light as it travels from one transparent medium to another can be used to form images.
Enduring Understanding 6.F Electromagnetic radiation can be modeled as waves or as fundamental particles.
Essential Knowledge 6.F.4 The nature of light requires that different models of light are most appropriate at different scales.
25.1 The Ray Aspect of Light
There are three ways in which light can travel from a source to another location. (See Figure 25.2.) It can come directly from the source through empty space, such as from the Sun to Earth. Or light can travel through various media, such as air and glass, to the person. Light can also arrive after being reflected, such as by a mirror. In all of these cases, light is modeled as traveling in straight lines called rays. Light may change direction when it encounters objects (such as a mirror) or in passing from one material to another (such as in passing from air to glass), but it then continues in a straight line or as a ray. The word ray comes from mathematics and here means a straight line that originates at some point. It is acceptable to visualize light rays as laser rays (or even science fiction depictions of ray guns).
Learning Objectives
By the end of this section, you will be able to:
• List the ways by which light travels from a source to another location.
The information presented in this section supports the following AP® learning objectives and science practices:
• 6.F.4.1 The student is able to select a model of radiant energy that is appropriate to the spatial or temporal scale of an interaction with matter. (S.P. 6.4, 7.1)
Ray
The word “ray” comes from mathematics and here means a straight line that originates at some point.
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