Interactions of Light with Matter Chapter 3 Section 2

How does light travel? In a straight line unless it hits object or is absorbed

What is reflection? Light bouncing off an object Changes direction of light Like a ball bouncing off ground

What is “Law of Reflection”? Angle made by light hitting surface = angle of light reflected

What are the types of Reflection”? Regular reflection: light reflects off mirror at same angle; surface smooth/ shiny – mirror

What are the types of Reflection? Diffuse reflection: light reflects in many directions; surface rough/bumpy – wall; can’t see reflection

What are the types of Reflection? Regular (Spectacular) Diffuse

What are the light sources? Luminous - object produces visible light Illuminated – object needs a separate light source to be seen Importance? Sight needs light; to be seen must either be luminous or be illuminated

Interactions of Light with Matter Chapter 3 Section 2 Part II

What is absorption of light? Transfer of energy to particles of matter Explains why light dims as it moves from light source: more particles absorb the energy, making it dimmer

What is scattering of light? Light moving in all directions after colliding with particles Fog is good example Allows you to see outside beam, but it dims Explains why sky is blue: shorter wavelength is scattered more than other colors, so you see more of it

How does light interact with matter? Reflected – bounces off Transmitted – passes through matter; example through a window Absorbed – transfer light energy to matter; makes object feel warmer (next section) Refracted – wave is bent

How does transparent, translucent, or opaque matter matter?  Transparent: easily transmits visible light (air, glass, H2O) Translucent: transmits light but also scatters it (wax paper) Opaque: doesn’t transmit light (metal, wood, textbook)

How is an object’s color determined? Wavelength determines Eyes receive light Eyes send messages to brain Brain interprets signals as colors Long = red / short = violet / mixture of waves = combination of colors

With opaque objects, how does reflection and absorption impact the color? Light hits opaque object: Some waves reflected, see that color Some absorbed, don’t see that color

How do we see a strawberry as red? Red wavelengths reflected; other colors’ wavelengths absorbed

What makes something white? All colors’ wavelengths are reflected

What makes something black? All colors’ wavelengths are absorbed

What about color in non-opaque objects? Transparent: Colorless in white light because all light waves pass through (transmit). Think of glass window. Translucent: Shows color of wavelength reflected or transmitted; all others absorbed. Think of stained glass.

How do pigments produce color? Pigment = material that absorbs some colors of light and reflects other

What has pigment? Pigment is in almost everything

What are two examples of pigments? Melanin = pigment for skin color Chlorophyll = plant color

What happens when pigments are mixed? Each pigment absorbs at least 1 color Mix pigments, more colors are taken away; color subtraction