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The Art of Bending Light. It’s what we see…. Refraction. the bending of light when passing through a new (transparent) substance. Bending Light: Vocabulary. Incident Ray Angle of Incidence Normal Refracted Ray Angle of Refraction. Optical Density.

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the art of bending light
The Art of Bending Light

It’s what we see…

refraction
Refraction
  • the bending of light when passing through a new (transparent) substance
bending light vocabulary
Bending Light: Vocabulary
  • Incident Ray
  • Angle of Incidence
  • Normal
  • Refracted Ray
  • Angle of Refraction
optical density
Optical Density
  • How difficult it is for light to movethrough a substance .
  • High optical density  light travels more slowly
  • Low optical density  light travels more quickly
optical density1
Optical Density
  • How difficult it is for light to movethrough a substance .
  • High optical density  light travels through more slowly
  • Low optical density  light travels through more quickly
low to high optical density
Low to High Optical Density

Where is the refracted angle?

FST:

Fast to SlowTowardsthe normal

low to much higher optical density
Low to much higher Optical Density

Where is the refracted angle?

FST:

Fast to SlowTowardsthe normal

high to lower optical density
High to lower Optical Density

Where is the refracted angle?

SFA:

Slow to FastAwayfromthe normal

quick ways to remember
Quick ways to remember…
  • FST = Fast to Slow, Towards Normal
    • FAST
    • FST = Freaky science teachers?
  • SFA = Slow to Fast, Away From Normal
    • SFA = Sarah Farts a lot?
slide11

Draw the path light takes from the penny to your eye.

  • Where will the light bend?
  • Which substance has a higher optical density?
  • What direction do you expect light to bend?
slide12
Why?
  • Imagine rows of hikers
  • From dry land to swamp
  • Hikers in swamp mud slow down
  • Others stay fast
  • Result: Change in Angle!
slide14
OR…
  • Pierre de Fermat
  • Fermat’s Principle
  • Light always takes fastest path
  • So…
fastest path
Fastest Path
  • Is a straight line always the fastest?
  • Where is light

traveling the fastest?

fast

slow

fastest path1
Fastest Path
  • Is a straight line always the fastest?
  • Dashed line is in slow substance for less time and in faster substance for more time.
  • Bent path is faster overall.

d1<d2

d2

fast

d1

slow

speeds of light
Speeds of Light
  • As light travels though different substances its speed changes
optical density2
Optical Density
  • Ratio of old to new speed
  • n =optical density
  • Also known as index of refraction
optical density3
Optical Density
  • c =speed of light in a vacuum
  • (3.00 x 108 m/s )
  •  = speed of light in substance

1. In what substance will light travel the fastest?

2. What number will n always be larger than?

speed of light
Speed of light
  • n = 1 in vacuum
  • Fastest in space. So…
  • n≥1 always!
index of refractions
Index of Refractions
  • Table of indices of refraction for various substances
working with air
Working with Air
  • In a vacuum,
  • n = 1
  • In air,
  • n = 1.0003
  • The difference is so small that air is treated like a vacuum
trigonometry review
Trigonometry “Review”
  • SOHCAHTOA
  • sin  =

IN

OS

AN

snell s law
Snell’s Law

n1= index of refraction 1

1 = incident angle

n2= index of refraction 2

2 = refracted angle

n1

1

2

n2

how to choose the equation

1

2

How to choose the Equation

ex) How fast is light in Water?

  • To find Speeds or optical density
  • To find angles or optical density
how fast is light in water
How fast is light in water?
  • n = 1.33
  • c = 3.00 x 108m/s
  • v = ?
slide28

Example 2A ray of light passes from water to quartz (n = 1.54). The angle of incidence in the water is 35°. What is the angle of refraction?

Water

n = 1.33

Given:

1

2

Quartz

n = 1.54

Unknown:

slide29

Example 2A ray of light passes from water to quartz (n = 1.54). The angle of incidence in the water is 35°. What is the angle of refraction?

Given:

Unknown:

slide31

Example 3Wesson oil was poured into the larger beaker until it flowed about half way up the smaller beaker. Why did the bottom of the beaker disappear?

  • Invisible: Light rays must be unchanged
  • Light does not bend between beakers
  • n1n2
slide32

Example 3Wesson oil was poured into the larger beaker until it flowed about half way up the smaller beaker. Why did the bottom of the beaker disappear?

oil

n = 1.47

1

pyrex

n = 1.47

2

slide33

Example 4The speed of light in a certain substance is 1.90 x 108m/s. If light passes from air into the substance at an angle of incidence of 54.0°, what will be the angle of refraction?

Given:

Unknown:

Find n first!

example 4
Example 4

Given:

Want:

snell s law song
Snell’s Law Song
  • Singin’ n1 sine theta-sub-1, hey-hey-hey, Equals n2 sine theta-sub-2, hip hooray
snell s law song1
Snell’s Law Song
  • Singin’ n1 sine theta-sub-1, hey-hey-hey, Equals n2 sine theta-sub-2, hip hooray
total internal reflection1
Total Internal Reflection
  • Optical fibers (Internet)
  • Rain sensors to control automatic windscreen/windshield wipers.
  • Binoculars
  • Multi-touch screens (IPAD!)
  • Fingerprinting devices
  • Double Rainbows
  • Eye doctors, to measure the angle between the eye's cornea and iris.
how far can light bend
How far can light bend?

No more refraction!

Light must now reflect

?

slide47

Sometimes light Reflects

  • Only possible when light travels from high n to lowbecause light needs to bend away from the normal
  • Occurs when

incident angle > critical angle

  • i> icritical
critical angle behavior
Critical Angle Behavior

air

air

air

air

glass

glass

glass

glass

calculating critical angle
Calculating Critical Angle

Use Snell’s Law

or

example
Example

What is the critical angle for light going from glass to air?(nglass= 1.50)

Given:

Unknown:

time to practice

Time to practice

go to pg. 98

white light dispersion
White Light Dispersion
  • Now we know refraction
  • but…
  • It’s more complicated than that.
  • Refraction actually varies for each color!
white light dispersion1
White Light Dispersion

The white light is separatedintoitscolors

time to practice1

Time to practice

Go to pg. 97

white light dispersion2
White Light Dispersion
  • Use Snell’s Law
  • draw normals
lenses
Lenses

Focal point

  • Draw normals
  • Middle ray on normal
  • Middle ray does not refract
  • Light rays converge!
  • CONVERGING LENS
lenses1
Lenses

Focal point

  • Normals again
  • Follow Rays Backwards!
  • Light rays diverge!
  • DIVERGING LENS
locating images of lenses
Locating Images of Lenses
  • Remember Mirror Ray Patterns?
  • Lenses also have patterns!
  • Let’s break ‘em down!
converging lens through center
Converging Lens: Through Center

Refract Straight through!

diverging lens parallel rays
Diverging Lens: Parallel Rays

Krikey! Away from f !

diverging lens towards f
Diverging Lens: Towards f

Ka’Pow! Parallel!

diverging lens through center
Diverging Lens: Through Center

Mamma Mia! Straight Through!

find the image
Find the Image

Region Locations:

  • Same side as object
  • Between f and 2f
  • At 2f
  • Beyond 2f
time to practice2

Time to Practice!

Go to pg. 72

thin lens equations
Thin Lens Equations
  • Time for a new equation…
  • or
multiple lenses
Multiple Lenses
  • Image of first lens is the object of the next!
galileo inquisition
Galileo Inquisition

Eppur Si Muove!

time to practice3

Time to Practice

Go to pg.85!