ch3 section2 light and matter.ppt
TRANSCRIPT
Interactions of Light with MatterInteractions of Light with MatterChapter 3 Section 2Chapter 3 Section 2
How does light travel?How does light travel?
• In a straight line unless it hits object or is absorbed
What is reflection?What is reflection?
• Light bouncing off an object
• Changes direction of light
• Like a ball bouncing off ground
What is “Law of Reflection”?What is “Law of Reflection”?
• Angle made by light hitting surface = angle of light reflected
What are the types of What are the types of Reflection”?Reflection”?
• Regular reflection: light reflects off mirror at same angle; surface smooth/ shiny – mirror
What are the types of What are the types of Reflection?Reflection?
• Diffuse reflection: light reflects in many directions; surface rough/bumpy – wall; can’t see reflection
What are the types of What are the types of Reflection?Reflection?
• Regular (Spectacular)
• Diffuse
What are the light sources?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 MatterInteractions of Light with MatterChapter 3 Section 2 Part IIChapter 3 Section 2 Part II
What is absorption of light?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?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? 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, How does transparent, translucent, or opaque matter matter? 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 How is an object’s color determined? 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 With opaque objects, how does reflection and absorption impact reflection and absorption impact
the color?the color?• Light hits opaque
object:Some waves reflected, see that colorSome absorbed, don’t see that color
How do we see a strawberry as How do we see a strawberry as red?red?
• Red wavelengths reflected; other colors’ wavelengths absorbed
What makes something white?What makes something white?
• All colors’ wavelengths are reflected
What makes something What makes something blackblack??
• All colors’ wavelengths are absorbed
What about color in non-opaque What about color in non-opaque objects?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 How do pigments produce color?color?
• Pigment = material that absorbs some colors of light and reflects other
What has pigment?What has pigment?
• Pigment is in almost everything
What are two examples of What are two examples of pigments?pigments?
• Melanin = pigment for skin color
• Chlorophyll = plant color
What happens when pigments are What happens when pigments are mixed?mixed?
• Each pigment absorbs at least 1 color
• Mix pigments, more colors are taken away; color subtraction