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It’s what we see… The Art of Bending Light

The Art of Bending Light

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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. - PowerPoint PPT Presentation

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Page 1: The Art of Bending Light

It’s what we see…

The Art of Bending Light

Page 2: The Art of Bending Light

Refraction•the bending of light when passing

through a new (transparent) substance

Page 3: The Art of Bending Light

Bending Light: Vocabulary

Incident RayAngle of

IncidenceNormalRefracted RayAngle of

Refraction

Page 4: The Art of Bending Light

Optical DensityHow difficult it is for light

to move through a substance .

High optical density light travels through more slowly

Low optical density light travels through more quickly

Page 5: The Art of Bending Light

Optical DensityHow difficult it is for light

to move through a substance .

High optical density light travels through more slowly

Low optical density light travels through more quickly

Page 6: The Art of Bending Light

Low to High Optical Density

Page 7: The Art of Bending Light

Low to much higher Optical Density

Page 8: The Art of Bending Light

High to lower Optical Density

Page 9: The Art of Bending Light

End Part I

Page 10: The Art of Bending Light

Quick Review

Notice when:

Light bends in

Light bends out

Page 11: The Art of Bending Light

Speeds of LightFast lightSlow light

Page 12: The Art of Bending Light

Optical DensityRatio of old to new speed

n =optical densityAlso known as

index of refractionc =speed of light =speed of light

in substance

Page 13: The Art of Bending Light

Speed of lightc = 3.00 x 108 m/sin a vacuumIn space, = c

n = 1 in vacuumFastest in space.

So…n≥1 always!

Page 14: The Art of Bending Light

Index of RefractionsTable of indices

of refraction for various substances

Page 15: The Art of Bending Light

Which substance has greatest n? Lowest?

Page 16: The Art of Bending Light

Trigonometry “Review”

SOHCAHTOA

sin =

IN OS AN

Page 17: The Art of Bending Light

Snell’s Law

Basic formCompares

angles1

2

d1

d2

Page 18: The Art of Bending Light

Working with AirIn a vacuum,n = 1

In air,n = 1.0003

Air is treated like a vacuum

Page 19: The Art of Bending Light

Snell’s Law from Air or Vacuum

In air, n = 1So, ignore n1Let’s solve for

n2

Page 20: The Art of Bending Light

How to choose the Equation

Speeds

Neither substance is air

One substance is air

ex) How fast is light in Water?

1

2

3

Page 21: The Art of Bending Light

How fast is light in water?n = 1.33c = 3.00 x 108 m/s

Page 22: The Art of Bending Light

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:

Want:

Page 23: The Art of Bending Light

Refraction Activity!

Go to pg. 64

Page 24: The Art of Bending Light

Example 3The photo below shows a smaller beaker inside a larger beaker. Wesson oil was poured into the larger beaker until it flowed about half way up the smaller beaker. Explain why the bottom of the beaker has disappeared.n1n2Light does not

bend between beakers

Page 25: The Art of Bending Light

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:

Want:Find n first!

Page 26: The Art of Bending Light

Example 4

Given:

Want:

Page 27: The Art of Bending Light

Why?

Imagine rows of hikers

From dry land to swamp

Hikers in swamp slow down

Others stay fastAngle Changed!

Page 28: The Art of Bending Light

OR…

Pierre de Fermat

Fermat’s Principle

Light always takes fastest path

So…

Page 29: The Art of Bending Light

Fastest PathIs a straight line

always the fastest?

Page 30: The Art of Bending Light

Fastest PathIs 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.

d2

d1

d1<d2

Page 31: The Art of Bending Light

Snell’s Law SongSingin’ n1 sine theta-sub-1, hey-hey-

hey, Equals n2 sine theta-sub-2, hip hooray

Page 32: The Art of Bending Light

Atmospheric Refraction Effects•Colors in the sky

•Air scatters light with small wavelengths•Every color has its own wavelength (λ)

Intensity of scattered light

Page 33: The Art of Bending Light

Draw normalsMiddle ray on

normalMiddle ray

does not refract

Light rays converge!

CONVERGING LENS

LensesFocal point

Page 34: The Art of Bending Light

Normals againFollow Rays

Backwards!Light rays diverge!DIVERGING LENS

LensesFocal point

Page 35: The Art of Bending Light

Locating Images of Lenses

Remember Mirror Ray Patterns?

Lenses also have patterns!

Let’s break ‘em down!

Page 36: The Art of Bending Light

Converging Lens: Parallel RaysHoly cow! Through f !

Page 37: The Art of Bending Light

Converging Lens: From fZOMG! Parallel!

Page 38: The Art of Bending Light

Converging Lens: Through CenterWowzers! Straight through!

Page 39: The Art of Bending Light

Diverging Lens: Parallel RaysKrikey! Away from f !

Page 40: The Art of Bending Light

Diverging Lens: Towards fKa’Pow! Parallel!

Page 41: The Art of Bending Light

Diverging Lens: Through Center

Mamma Mia! Straight Through!

Page 42: The Art of Bending Light

Find the ImageRegion Locations:

• Same side as object

• Between f and 2f• At 2f• Beyond 2f

Page 43: The Art of Bending Light

Time to Practice!

Go to pg. 72

Page 44: The Art of Bending Light

Lens Movie

Page 45: The Art of Bending Light

Thin Lens EquationsTime for a new

equation…

or

Page 46: The Art of Bending Light

Signs and LensesFocal LengthConverging Lens

Positive f

Diverging Lens Negative f

Page 47: The Art of Bending Light

Signs and LensesImage DistanceImage on same side as object

Negative di Virtual Image

Image on opposite side

Positive di Real Image

Page 48: The Art of Bending Light

Magnification EquationIntroducing…

Page 49: The Art of Bending Light

Multiple LensesImage of first lens

is the object of the next!

Page 50: The Art of Bending Light

Galileo InquisitionEppur Si Muove!

Page 51: The Art of Bending Light

Time to PracticeGo to pg. 85!

Page 52: The Art of Bending Light

Total Internal Reflection

Page 53: The Art of Bending Light

Total Internal Reflection

?

No more refraction! Light must

now reflect

Page 54: The Art of Bending Light

Only when going from high to low n

Refracted angles go up to 90°

After that, no refraction

When r = 90°, i is called the critical angle

Total Internal Reflection

Page 55: The Art of Bending Light

Critical Angle Behavior1. Critical angle shown2. i < ic (critical angle)3. i = ic light moves

between4. i > ic totally reflected

Page 56: The Art of Bending Light

Calculating Critical Angle

Use Snell’s Law

or

Page 57: The Art of Bending Light

ExampleWhat is the critical angle for glass?(n = 1.50)Given:

Want:

Page 58: The Art of Bending Light

Time to practicego to pg. 84

Page 59: The Art of Bending Light

White Light Dispersion Now we know

refraction but… It’s more

complicated than that.

Refraction actually varies for each color!

Page 60: The Art of Bending Light

White Light Dispersion

The white light is separated into its colors

Page 61: The Art of Bending Light

Time to practice

Go to pg. 89

Page 62: The Art of Bending Light

White Light Dispersion Use Snell’s

Law draw normals