## How We See Things/7

### What is it about objects that let us see them? Why do we see the road, or a pen, or a best friend? If an object does not emit its own light (which accounts for most objects in the world), it must reflect light in order to be seen. The walls in the room that you are in do not emit their own light; they reflect the light from the ceiling "lights" overhead. Polished metal surfaces reflect light much like the silver layer on the back side of glass mirrors. A beam of light incident on the metal surface is reflected. Reflection involves two rays - an incoming or incident ray and an outgoing or reflected ray. In Figure 1 we use a single line to illustrate a light ray reflected from the surface. The law of reflection requires that two rays are at identical angles but on opposite sides of the normal which is an imaginary line (dashed in Fig. 1) at right angles to the mirror located at the point where the rays meet. We show in Fig. 1 that the angles of incidence i and reflection i' are equal by joining the two angles with an equal sign.

#### Last Updated: 5th Aug 2016

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