chapter 22probe

Chapter 22: LightChapter 22: Light

What is light?What is light?

It is an electromagnetic wave (EM It is an electromagnetic wave (EM wave).wave).

Does not require a medium to Does not require a medium to traveltravel

Consists of changing electric and Consists of changing electric and magnetic fields (fields are forces magnetic fields (fields are forces that push and pull on another that push and pull on another object without touching it)object without touching it)

Why are EM waves Why are EM waves really transverse really transverse waves?waves? The electric and magnetic fields The electric and magnetic fields

travel at right angles to each travel at right angles to each other (in other words they are other (in other words they are perpendicular to one another)perpendicular to one another)

And the fields travel And the fields travel perpendicular to the direction of perpendicular to the direction of the motionthe motion

How are EM waves How are EM waves produced?produced? By the vibration of an electrically By the vibration of an electrically

charged particlecharged particle When the electron absorbs energy it When the electron absorbs energy it

will jump orbital levelswill jump orbital levels Eventually, the e will move back down Eventually, the e will move back down

releasing a burst of energy called a releasing a burst of energy called a photonphoton

The constant stream of photons create The constant stream of photons create the EM waves and it is called radiation.the EM waves and it is called radiation.

How do you calculate How do you calculate the speed of light?the speed of light? Through a vacuum (in space- not Hoover), Through a vacuum (in space- not Hoover),

light travels about 300,000,000 m/slight travels about 300,000,000 m/s Light travels slightly slower through air, Light travels slightly slower through air,

glass, and other types of matterglass, and other types of matter Light travels more than 880,000 times Light travels more than 880,000 times

faster than soundfaster than sound Tidbit: if you could run as fast as light, you Tidbit: if you could run as fast as light, you

will circle the Earth 7.5 times in 1 sec.will circle the Earth 7.5 times in 1 sec.

Math BreakMath Break

Speed = distance / timeSpeed = distance / time Time = distance / speedTime = distance / speed EX: time = 382,000,000 m / EX: time = 382,000,000 m /

300,000,000 m/s300,000,000 m/s1.1. Time = 1.27 sTime = 1.27 s You try this: The earth is You try this: The earth is

150,000,000,000 m from the sun. How 150,000,000,000 m from the sun. How long does it take for the light to travel long does it take for the light to travel that distance?that distance?

500 s or 8.3 mins.500 s or 8.3 mins.

I. Electromagnetic I. Electromagnetic RadiationRadiation

EM RadiationEM Radiation EM SpectrumEM Spectrum Types of EM RadiationTypes of EM Radiation

A. EM RadiationA. EM Radiation

Electromagnetic RadiationElectromagnetic Radiation– transverse waves produced by the motion of transverse waves produced by the motion of

electrically charged particleselectrically charged particles– does not require a mediumdoes not require a medium– speed in a vacuum = 300,000 km/sspeed in a vacuum = 300,000 km/s– electric and magnetic electric and magnetic

components are components are perpendicularperpendicular

A. EM RadiationA. EM Radiation

PhotonsPhotons– tiny, particle-like tiny, particle-like

bundles of radiationbundles of radiation– absorbed and absorbed and

released by electronsreleased by electrons

energy increases with wave frequency

B. EM SpectrumB. EM Spectrum

long

low f

low energy

short

high f

high energy

C. Types of EM RadiationC. Types of EM Radiation

RadiowavesRadiowaves– lowest energy EM radiationlowest energy EM radiation


RadiowavesRadiowaves– FM - frequency modulation FM - frequency modulation – AM - amplitude modulationAM - amplitude modulation

Microwavespenetrate food and vibrate

water & fat molecules to produce thermal energy


Infrared RadiationInfrared Radiation (IR)(IR)– slightly lower energy than slightly lower energy than

visible lightvisible light– can raise the thermal can raise the thermal

energy of objectsenergy of objects– thermogramthermogram - image made - image made

by detecting IR radiationby detecting IR radiation


Visible LightVisible Light– small part of small part of

the spectrum the spectrum we can seewe can see

– ROY G. BIV - ROY G. BIV - colors in order colors in order of increasing of increasing energyenergy R O Y G. B I V

red orange yellow green blue indigo violet


Ultraviolet Radiation (UV)Ultraviolet Radiation (UV)– slightly higher energy than visible lightslightly higher energy than visible light– TypesTypes::

UVA - tanning, wrinklesUVA - tanning, wrinkles UVB - sunburn, cancerUVB - sunburn, cancer UVC - most harmful, UVC - most harmful,

sterilization sterilization


Ultraviolet Radiation (UV)Ultraviolet Radiation (UV)– Ozone layer depletion = UV exposure!Ozone layer depletion = UV exposure!

Warm-upWarm-up Explain what properties you Explain what properties you

would use and how you would use would use and how you would use them to explain the difference them to explain the difference between salt and sandbetween salt and sand

Properties

I would……


X raysX rays– higher energy than UVhigher energy than UV– can penetrate soft can penetrate soft

tissue, but not bonestissue, but not bones


Gamma raysGamma rays– highest energy highest energy

EM radiationEM radiation– emitted by emitted by

radioactive radioactive atomsatoms

– used to kill used to kill cancerous cellscancerous cells Radiation treatment using

radioactive cobalt-60.

Warm-upWarm-up

Identify the medium through Identify the medium through which the wave is travelingwhich the wave is traveling

Interactions of LightInteractions of Light

Light can reflect, refract, be Light can reflect, refract, be absorbed, be scattered, diffract, absorbed, be scattered, diffract, and interferenceand interference

ReflectionReflection

The bouncing back of a wave The bouncing back of a wave when it strikes a surfacewhen it strikes a surface

Law of Reflection states that the Law of Reflection states that the angle of incidence is equal to the angle of incidence is equal to the angle of reflection.angle of reflection.

2 types: regular reflection and 2 types: regular reflection and diffused reflectiondiffused reflection

Types of ReflectionTypes of Reflection

– A A regular reflectionregular reflection is the striking of is the striking of light rays at the same time. It is off light rays at the same time. It is off a smooth surface. (Think of a ball a smooth surface. (Think of a ball bouncing off the pavement)bouncing off the pavement)

– A A diffuse reflectiondiffuse reflection is the striking of is the striking of light rays at uneven time. It is off a light rays at uneven time. It is off a bumpy surface. The light rays bumpy surface. The light rays bounce in different directions. (Think bounce in different directions. (Think of a ball bouncing off an uneven of a ball bouncing off an uneven surface)surface)

Law of ReflectionLaw of Reflection

AbsorptionAbsorption

The transfer of light energy to particles The transfer of light energy to particles of matterof matter

the frequency of the incoming light the frequency of the incoming light wave is at or near the energy levels of wave is at or near the energy levels of the electrons in the matter. The the electrons in the matter. The electrons will absorb the energy of the electrons will absorb the energy of the light wave and change their energy light wave and change their energy state. state.

ScatteringScattering

The release of light energy by The release of light energy by particles of matter that have particles of matter that have absorbed energyabsorbed energy

RefractionRefraction

The bending of light wave as it The bending of light wave as it passes as an angle from one passes as an angle from one medium to the nextmedium to the next

Bends due to the change of speed Bends due to the change of speed of light through the different of light through the different mediamedia

Creates the rainbow, optical Creates the rainbow, optical illusionsillusions

B. RefractionB. Refraction

Refraction depends Refraction depends on…on…

– speed of light in speed of light in the mediumthe medium

– wavelength of wavelength of the light - shorter the light - shorter wavelengths (blue)wavelengths (blue)bend morebend more

B. RefractionB. Refraction

Example:Example:

View explanation.

Optical IllusionsOptical Illusions

How your brain interprets the How your brain interprets the light waves travelinglight waves traveling

Follow the pink dots and Follow the pink dots and they remain pink; stare they remain pink; stare at the black center and at the black center and they become greenthey become green

Face or flowers

Do you see the man’s Do you see the man’s head?head?

Do you see a musician Do you see a musician or girl’s face?or girl’s face?

How many people you How many people you see in the picture?see in the picture?

Find the man’s faceFind the man’s face

Is this picture moving?Is this picture moving?

Horse on a rock?Horse on a rock?

Rabbit or Duck?Rabbit or Duck?

Can you count the Can you count the black dots?black dots?

DiffractionDiffraction

Light can diffract.Light can diffract. However, it can only diffract However, it can only diffract

around smaller objects.around smaller objects. The outside of the light gets fuzzy The outside of the light gets fuzzy

when diffracting.when diffracting.

C. DiffractionC. Diffraction

DiffractionDiffraction

– bending of waves bending of waves around a barrieraround a barrier

– longer wavelengths longer wavelengths (red) bend more - (red) bend more - opposite of refractionopposite of refraction

InterferenceInterference

Does happenDoes happen Can see constructive interferenceCan see constructive interference Destructive interference is very Destructive interference is very

rarerare

D. InterferenceD. Interference

InterferenceInterference– constructive constructive brighter light brighter light– destructive destructive dimmer light dimmer light

E. Cool Applications!E. Cool Applications!

Fiber OpticsFiber Optics– Total Internal ReflectionTotal Internal Reflection

when all light is reflected back when all light is reflected back into the denser medium into the denser medium


The “Broken Pencil”The “Broken Pencil”– refractionrefraction

View animation and explanation of the “Broken Pencil.”


RainbowsRainbows– refraction-reflection-refractionrefraction-reflection-refraction


Diffraction GratingsDiffraction Gratings– glass or plastic made up glass or plastic made up

of many tiny parallel of many tiny parallel slitsslits

– may also be reflectivemay also be reflective– spectroscopes, spectroscopes,

reflective rainbow reflective rainbow stickers, CD surfacesstickers, CD surfaces


Thin Films - Bubbles & Oil SlicksThin Films - Bubbles & Oil Slicks– interference results from double reflectioninterference results from double reflection


Blue Sky & Red SunsetsBlue Sky & Red Sunsets

NOON• less atmosphere• less scattering• blue sky, yellow

sun

SUNSET• more atmosphere• more scattering• orange-red sky & sun

• Molecules in atmosphere scatter light rays.

• Shorter wavelengths (blue, violet) are scattered more easily.

Light and ColorLight and Color Light and MatterLight and Matter Seeing ColorsSeeing Colors Mixing ColorsMixing Colors

A. Light and MatterA. Light and Matter

OpaqueOpaque– absorbs or reflects all lightabsorbs or reflects all light

TransparentTransparent– allows light to pass through allows light to pass through

completelycompletely

TranslucentTranslucent– allows some light to pass throughallows some light to pass through

B. Seeing ColorsB. Seeing Colors

White lightWhite light– contains all visible colors - ROY G. BIVcontains all visible colors - ROY G. BIV

In white light, an object…In white light, an object…– reflects the color you seereflects the color you see– absorbs all other colorsabsorbs all other colors

REFLECTSALL COLORS

ABSORBSALL COLORS


The retina contains…The retina contains…– RodsRods - dim light, black & white - dim light, black & white– ConesCones - color - color

red - absorb red & yellowred - absorb red & yellow green - absorb yellow & greengreen - absorb yellow & green blue - absorb blue & violetblue - absorb blue & violet

Stimulates red & green cones

Stimulates all cones


Color BlindnessColor Blindness– one or more sets of one or more sets of

cones does not cones does not function properlyfunction properly

Test for red-green color blindness.

C. Mixing ColorsC. Mixing Colors

Primary Primary light colorslight colors– red, green, bluered, green, blue

– additive colorsadditive colors

– combine to form white combine to form white lightlight

View Java Applet on primary light colors.

EX: computer RGBs


FilterFilter– transparent transparent

material that material that absorbs all light absorbs all light colors except the colors except the filter colorfilter color

View Java Applet on filters.


PigmentPigment– colored material that absorbs colored material that absorbs

and reflects different colorsand reflects different colors

Primary pigment colorsPrimary pigment colors– cyan, magenta, yellowcyan, magenta, yellow– subtractive colorssubtractive colors– combine to form blackcombine to form black

EX: color ink cartridges


Light Pigment

When mixing pigments, the color of the mixture is the color of light that both pigments reflect.

Negative Afterimage - One set of cones gets tired, and the remaining cones produce an image in the complimentary color.

chapter 22probe

Documents

interactions of light

speed of light

light waves

transfer of light energy

release of light energy

visible light types

ir radiation

em waves