Ch 16Ch 16

Light WavesLight Waves

LightLight

We see objects because light is either We see objects because light is either emitted or reflected by the objectemitted or reflected by the object

LightLight

Light is an electromagnetic wave that the human Light is an electromagnetic wave that the human eye can detecteye can detect

Light has wavelengths that range from 400 nm Light has wavelengths that range from 400 nm (violet) to 700 nm (red)(violet) to 700 nm (red)

The speed of light is 3 EE 8 m/sThe speed of light is 3 EE 8 m/s

Luminous BodyLuminous Body

Emits light wavesEmits light waves Ex: the sunEx: the sun

Illuminated BodyIlluminated Body

Reflects light wavesReflects light waves Ex: the moonEx: the moon

Luminous Flux (P)Luminous Flux (P)

The rate at which light is emitted from a The rate at which light is emitted from a sourcesource

It is measured in lumen (lm)It is measured in lumen (lm)

Illuminance (E)Illuminance (E)

The amount of light that is reflectedThe amount of light that is reflectedE = E = PP

44ππdd22

Units are lm/mUnits are lm/m22 or lux (lx) or lux (lx)

Luminous Intensity (I)Luminous Intensity (I)

Luminous flux that falls on one square Luminous flux that falls on one square meter of a sphere one meter in radiusmeter of a sphere one meter in radius

I = I = PP

44ππUnits are candela (cd)Units are candela (cd)

Types of MaterialsTypes of Materials

TransparentTransparent

Transmits light Transmits light without distortionwithout distortion

Ex: crystal clear waterEx: crystal clear water

TranslucentTranslucent

Transmits light but the Transmits light but the image is distortedimage is distorted

Ex: lampshadeEx: lampshade

OpaqueOpaque

Transmits no light Transmits no light All light is absorbed or All light is absorbed or

reflectedreflected Ex: brickEx: brick

White LightWhite Light

Produced by adding the colors Produced by adding the colors redred, , blueblue and and greengreen

This is called the additive processThis is called the additive process RedRed, , blueblue and and greengreen are called the primary light are called the primary light

colorscolors

Mixing Light ColorsMixing Light Colors

RedRed and and GreenGreen = = BlueBlue and and GreenGreen = = RedRed and and BlueBlue = =

YellowYellow CyanCyan MagentaMagenta

Complementary Light ColorsComplementary Light Colors

YellowYellow and and BlueBlue CyanCyan and and RedRed MagentaMagenta and and GreenGreen

Produce white lightProduce white light

Dyes and PigmentsDyes and Pigments

Dyes are molecules that dissolve in liquids Dyes are molecules that dissolve in liquids to form colored solutions. They absorb to form colored solutions. They absorb certain wavelengths and reflect others.certain wavelengths and reflect others.

A pigment also absorbs certain A pigment also absorbs certain wavelengths and reflects others, but they wavelengths and reflects others, but they are larger and mix to form suspensions.are larger and mix to form suspensions.

Dyes and PigmentsDyes and Pigments

The absorption process of light forms colors by The absorption process of light forms colors by the subtractive processthe subtractive process

Primary PigmentsPrimary PigmentsAbsorb one color from white light and reflect 2 colorsAbsorb one color from white light and reflect 2 colors

YellowYellow absorbs absorbs BlueBlue MagentaMagenta absorbs absorbs

GreenGreen CyanCyan absorbs absorbs RedRed

Reflects Reflects red red and and GreenGreen Reflects Reflects BlueBlue and and RedRed

Reflects Reflects BlueBlue and and GreenGreen

Secondary PigmentsSecondary PigmentsAbsorb 2 colors from white light and reflect one colorAbsorb 2 colors from white light and reflect one color

RedRed absorbs absorbs GreenGreen and and BlueBlue ( (CyanCyan))

GreenGreen absorbs absorbs RedRed and and BlueBlue ( (MagentaMagenta))

BlueBlue absorbs absorbs RedRed and and GreenGreen ( (yellowyellow))

Reflects Reflects RedRed

Reflects Reflects GreenGreen

Reflects Reflects BlueBlue

Complementary PigmentsComplementary Pigments

Produce black lightProduce black lightBlack is not a color just the absence of Black is not a color just the absence of

lightlightNo light is being reflectedNo light is being reflectedNote: The primary light colors are the Note: The primary light colors are the

secondary pigments and vice versasecondary pigments and vice versa

What color would a yellow banana What color would a yellow banana appear if it is hit with green light?appear if it is hit with green light?

Answer:Answer:Green, yellow can reflect red and green, Green, yellow can reflect red and green,

but there is only green light hitting it.but there is only green light hitting it.

What color would a yellow banana What color would a yellow banana appear if it is hit with blue light?appear if it is hit with blue light?

Answer:Answer:Black, the yellow absorbs blue light so Black, the yellow absorbs blue light so

there is no light to reflectthere is no light to reflect

What color would a yellow banana What color would a yellow banana appear if it is hit with cyan light?appear if it is hit with cyan light?

Answer:Answer:Green, the yellow absorbs blue lightGreen, the yellow absorbs blue lightCyan – Blue = GreenCyan – Blue = Green

Polarized LightPolarized Light

Light that only Light that only vibrates in one plane.vibrates in one plane.

Polarized light will Polarized light will only pass through a only pass through a polarized filter if it is polarized filter if it is parallel to the parallel to the vibrating lightvibrating light

Thin Film InterferenceThin Film Interference

The beautiful colors The beautiful colors are caused when light are caused when light reflects off of 2 reflects off of 2 surfacessurfaces

Example: Oil and Example: Oil and water or the 2 layers water or the 2 layers of a bubbleof a bubble