Name: ______
Block: ____
Notes: Getting in Light’s Way (10.2/10.3)
Two Models of Light
- particle model: represents light as a stream of fast-moving, tiny particles that travel in a straight line
- wave model: represents light traveling in waves (accounts for different colours of light)
- both correctly describe some properties of light, but neither one describes all of its properties
- to study optics it is helpful to use the ray model, which represents light in straight lines and shows the direction the light wave is travelling
Shadows
- shadow: an area where light has been blocked by a solid object
- umbra: the dark part of a shadow
- penumbra: the lighter part of a shadow (only present when the light source is larger than the object)
- to make a ray diagram, which shows you where the shadow and its parts will be, you need to draw rays from both the top and bottom of the light source to both the top and the bottom of the object (you should have four light rays in the end)
- if the light source is smaller than or close in size to the object, then just draw rays coming from the light source to the top and bottom of the object
Transparency
- transparency: a measure of how much light can pass through a material
- three classifications: transparent, translucent, opaque
- transparent: describes a material that transmits light (lets it pass through) easily and through which a clear image can be seen. eg. plate glass, air, shallow clear water
- translucent: describes a material that transmits light but also reflects some, so that a clear image cannot be seen through the material. eg. frosted glass, clouds, skin, fingernails
- opaque: describes a material that does not allow any light to be transmitted because all of it is either absorbed or reflected. eg. wood, stone, brick, milk, etc. (most materials)
- some materials may be transparent, translucent, or opaque depending on their thickness or how much of it you have
- eg. rock is normally opaque but if you cut a very thin slice off, it is translucent
- eg. shallow clear water is transparent, deeper clear water is translucent, and very deep clear water is opaque
Absorbing and Reflecting Light
- colour, sheen (shininess), and texture determine the amount of light energy that is absorbed or reflected
- black and dark-coloured materials absorb more light than light-coloured ones
- dull materials like wood absorb more light than shiny materials like aluminum
- rough-surfaced materials like stucco absorb more light than smooth-surfaced materials like plaster