Interactions of Light Waves Unit 14 Section 3

I. Light Interactions When light interacts with matter, it can be: Reflected Absorbed or scattered Refracted

II. Reflection a. Occurs when light waves bounce off an object. b. In order to reflect well, light needs a hard and smooth surface.

III. Absorption Absorption is the transfer of energy carried by light waves to particles of matter. Absorption explains why a beam of light from a flashlight appears dim - the particles in the air absorb (take in) some of the energy from the light. The further the light travels the more it is absorbed by the particles and the dimmer it becomes.

b. Absorption is when light waves hit a non-reflecting surface (ex-tennis ball). The light waves are absorbed (sucked in) by the object. However, the light waves that are the same color as the object are NOT absorbed (yellow tennis ball), they are reflected off (bounce off) of the surface (tennis ball) and are transmitted into our eye. 1. Example-If you are wearing a green shirt, green is being reflected and all other colors are being absorbed. 2. Example-If a chair is blue, blue is being reflected and all other colors are being absorbed.

When we see black, all colors are being absorbed and NO colors are being reflected. When we see white, no colors are being absorbed and ALL colors are being reflected. (all colors together = white)

IV. Refraction It is the bending of a wave as it passes between two substances (media). Refraction occurs because the wave speed changes as it enters a different medium. 1. You see the straw in air and glass/water (different media). 2. Air is the least dense and glass is the most dense.. So light waves will slow down as they enter denser media The denser the media, the slower light waves travel. Light speed: In gases light waves travel at a fast speed. In liquids, light waves travel at a medium speed. In solids, light waves travel the slowest speed. e. This is OPPOSITE from sound waves.

V. Refraction & Optical Illusions When light reflects off an object, it travels in a straight line from the object to your eye. BUT, when you look at an object that is underwater, the light reflecting off the object REFRACTS - therefore creating an optical illusion.

VI. Color Separation Remember that white light is composed (made) of all the wavelengths of visible light (ROYGBIV). When white light is refracted (bent), the amount that the light bends depends on its wavelength. Shorter wavelengths (violet-blue) bend more than longer wavelengths (red). Rainbows are created when sunlight (white light) is refracted by water droplets. 1. The sunlight went from air to liquid (a denser media) so the wave slowed down and changed direction.