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