10.2/10.3 Light’s Way

Light Models Sir Isaac Newton believed that light is a stream of fast-moving, unimaginably tiny particles, called the particle model of light Light also has properties that are best described using waves, such as the use of wavelength and frequency to account for the different colours of light. The particle model and the wave model correctly describe some properties of light, but neither one describes all of light’s properties The ray model represents light travelling in straight lines and shows the direction the light wave/particle is traveling.

Transparent material allows light to pass through freely (transmitted) Opaque material prevents any light from passing though it (absorbed) Translucent material allows some rays to get through, but the rays are scattered in all directions (reflected) Wood, stone, brick Frosted glass, clouds, fingernails, skin air, shallow clear water Transparency

Absorbing and Reflecting Light When light strikes an opaque material, no light passes through Some of the light energy is absorbed by the material and is converted into thermal energy. Colour, sheen (shininess), and texture are three properties that 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

Shadows is an area where light has been blocked by a solid object You can use the ray model to predict where shadows will form and how large they will be.

Watching Light Travel When the object is bigger than the source umbra: the dark part of a shadow To make a ray diagram, just draw rays coming from the light source to the top and bottom of the object

Watching Light Travel When the object is smaller than the source penumbra: the lighter part of a shadow To make a ray diagram, 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)