10.3: The Ray Model of Light

Different Materials Transparent Opaque Translucent Light passes through freely. A small amount of light is absorbed or reflected. Prevents any light from passing through it. It will only absorb or reflect light. Different Materials Translucent Most light rays pass through, but are scattered in all directions.

Recall: Light travels in a straight line. SHADOWS Recall: Light travels in a straight line. Solid Object Shadow

A shadow is formed where light is 'missing' A shadow is formed where light is 'missing'. A dark shadow (umbra) is formed where no light falls and a light shadow (penumbra) is formed where some light falls, but some is blocked. If the light source is very tiny and concentrated in one place (a point source) only a sharp shadow is formed.

SHADOWS: object & screen

If the source is broader light from the top of the source causes a lower shadow than that from the top. You therefore get partial shadow or penumbra as well as umbra.

CHANGES IN SIZE OF SHADOWS The size of a shadow changes as you move the source closer or further from the screen

or as you move the object closer or further from the screen.

If there is only one point source of light, then when it is blocked, no light will reach the shadowed area and the shadow will be dark. If there is a lot of reflection, diffuse light, or multiple light sources, however, the shadow will be lighter. Shadows Outside On a sunny day, most of the light is coming directly from the sun, but some of it is coming as blue scattered light coming from the sky. If you stand in front of the sun, the sun's light is blocked, but your shadow still receives light from the rest of the sky, and you can still see the shadowed ground. 

On a cloudy day, the light is completely diffuse, not coming from anywhere in particular, and you don't cast much of a shadow at all. 

Terminology Incident light ray incoming ray Reflected light ray ray that bounces off the barrier

An imaginary line that is perpendicular to the barrier. Normal An imaginary line that is perpendicular to the barrier. Normal Reflected Ray Incident Ray

Angle of incidence formed by the incident ray and the normal Angle of reflection formed by the reflected ray and the normal.

Angle of incidence is always equal to the reflected angle Reflection