Why does light behave the way it does with various materials? The Ray Model of Light Why does light behave the way it does with various materials?

Interacting with Light Often without even know it, we have to alter certain situations to better see something due to light reflection. Sometimes it’s light from the window reflecting off a computer or TV screen that prevents us from reading the screen Most of us know the properties of light and its interaction with other materials without ever picking up a book to study it In this section you will start to put a name and scientific reason to some of these properties

The Ray Model of Light In this model, light is represented as straignt lines called rays. We often use ray diagrams to depict how light travels in certain situations.

Ray Model of Light (cont’d) As mentioned in the last slide, light travels in straight lines It does this until it hits something Different materials will potentially interact with the light differently

Transparent Materials Some materials will let light go through and are called transparent materials. An example of a transparent material is clear glass Notice how the glass in this lantern allows all of the light through

Translucent Materials Some materials transmit some of the light, but not all of it and are called translucent materials. An example of a translucent material is a frosted window pane Notice how the glass in this lantern only allows some of the light through

Opaque Materials Materials that absorb light and reflect light, but do not transmit material are called opaque materials. An example of an opaque material is a black piece of cardboard Notice how the metal in the shade of this lamp does not allow any of the light through.

Shadows Ray diagrams can also explain the size and location of shadows. Sometimes shadows can be sharp and well defined like in the case of a small light source such as a small flashlight Other times they may have less defined edges and this is caused by very bright light sources such as the sun A shadow can have two parts: The umbra: the part of the shadow where all of the light rays have been blocked The penumbra: an area of partial shadow from a large light source

Shadows (cont’d) This diagram illustrates the umbra and penumbra from a larger light source, the sun.

Light Reflection Light travels in parallel lines When they hit a smooth surface, they will reflect off the surface parallel to one another This is called regular reflection When regular reflection occurs, it is possible to see an image in the reflection. A plane mirror is an example of such a surface.

Light Reflection (cont’d) An object can still reflect light even if it does not produce an image. Materials that are rough will cause light to be scattered in many directions This type of reflection is called diffuse reflection. One can see how light reflects in many directions off the rough surface. Though it appears smooth, the surface of the page of your textbook is rough. This allows one to see read the page from almost any angle.

Activity Some Properties of Light Go to page 407 in the Pearson Investigation Science 10 textbook and do the activity Some Properties of Light. Do questions 6 – 10. Put your answers on page 2 of the title page for this lesson.