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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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It’s what we see…
The Art of Bending Light
Refraction•the bending of light when passing
through a new (transparent) substance
Bending Light: Vocabulary
Incident RayAngle of
IncidenceNormalRefracted RayAngle of
Refraction
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
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
Low to High Optical Density
Low to much higher Optical Density
High to lower Optical Density
End Part I
Quick Review
Notice when:
Light bends in
Light bends out
Speeds of LightFast lightSlow light
Optical DensityRatio of old to new speed
n =optical densityAlso known as
index of refractionc =speed of light =speed of light
in substance
Speed of lightc = 3.00 x 108 m/sin a vacuumIn space, = c
n = 1 in vacuumFastest in space.
So…n≥1 always!
Index of RefractionsTable of indices
of refraction for various substances
Which substance has greatest n? Lowest?
Trigonometry “Review”
SOHCAHTOA
sin =
IN OS AN
Snell’s Law
Basic formCompares
angles1
2
d1
d2
Working with AirIn a vacuum,n = 1
In air,n = 1.0003
Air is treated like a vacuum
Snell’s Law from Air or Vacuum
In air, n = 1So, ignore n1Let’s solve for
n2
How to choose the Equation
Speeds
Neither substance is air
One substance is air
ex) How fast is light in Water?
1
2
3
How fast is light in water?n = 1.33c = 3.00 x 108 m/s
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:
Refraction Activity!
Go to pg. 64
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
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!
Example 4
Given:
Want:
Why?
Imagine rows of hikers
From dry land to swamp
Hikers in swamp slow down
Others stay fastAngle Changed!
OR…
Pierre de Fermat
Fermat’s Principle
Light always takes fastest path
So…
Fastest PathIs a straight line
always the fastest?
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
Snell’s Law SongSingin’ n1 sine theta-sub-1, hey-hey-
hey, Equals n2 sine theta-sub-2, hip hooray
Atmospheric Refraction Effects•Colors in the sky
•Air scatters light with small wavelengths•Every color has its own wavelength (λ)
Intensity of scattered light
Draw normalsMiddle ray on
normalMiddle ray
does not refract
Light rays converge!
CONVERGING LENS
LensesFocal point
Normals againFollow Rays
Backwards!Light rays diverge!DIVERGING LENS
LensesFocal point
Locating Images of Lenses
Remember Mirror Ray Patterns?
Lenses also have patterns!
Let’s break ‘em down!
Converging Lens: Parallel RaysHoly cow! Through f !
Converging Lens: From fZOMG! Parallel!
Converging Lens: Through CenterWowzers! Straight through!
Diverging Lens: Parallel RaysKrikey! Away from f !
Diverging Lens: Towards fKa’Pow! Parallel!
Diverging Lens: Through Center
Mamma Mia! Straight Through!
Find the ImageRegion Locations:
• Same side as object
• Between f and 2f• At 2f• Beyond 2f
Time to Practice!
Go to pg. 72
Lens Movie
Thin Lens EquationsTime for a new
equation…
or
Signs and LensesFocal LengthConverging Lens
Positive f
Diverging Lens Negative f
Signs and LensesImage DistanceImage on same side as object
Negative di Virtual Image
Image on opposite side
Positive di Real Image
Magnification EquationIntroducing…
Multiple LensesImage of first lens
is the object of the next!
Galileo InquisitionEppur Si Muove!
Time to PracticeGo to pg. 85!
Total Internal Reflection
Total Internal Reflection
?
No more refraction! Light must
now reflect
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
Critical Angle Behavior1. Critical angle shown2. i < ic (critical angle)3. i = ic light moves
between4. i > ic totally reflected
Calculating Critical Angle
Use Snell’s Law
or
ExampleWhat is the critical angle for glass?(n = 1.50)Given:
Want:
Time to practicego to pg. 84
White Light Dispersion Now we know
refraction but… It’s more
complicated than that.
Refraction actually varies for each color!
White Light Dispersion
The white light is separated into its colors
Time to practice
Go to pg. 89
White Light Dispersion Use Snell’s
Law draw normals