CHAPTER 22 CHAPTER 22 Reflection Reflection and and Refraction Refraction of Light of Light A is A “Something cannot be itself and something else at the same time.” Aristotle Light exhibits wave-like properties when studied under certain conditions. Light exhibits particle-like properties when studied under certain conditions. Light does not exhibit wave-like and particle-like properties simultaneously.
A is A “Something cannot be itself and something else at the same time.” Aristotle Light exhibits wave-like properties when studied under certain conditions. Light exhibits particle-like properties when studied under certain conditions. - PowerPoint PPT Presentation
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CHAPTER 22CHAPTER 22Reflection Reflection andand Refraction of Light Refraction of Light
A is A
“Something cannot be itself and something else at the same time.”
Aristotle
Light exhibits wave-like properties when studied under certain conditions.
Light exhibits particle-like properties when studied under certain conditions.
Light does not exhibit wave-like and particle-like properties simultaneously.
Properties of LightProperties of LightSpeed:Speed:
In a vacuum (c): 2.997924574x108m/s
c = 3.00x108m/s
In other mediums: Speed of light is less than c.Nothing can travel faster than the speed of light.
Direction:Direction: Light travels in a straight line path until it encounters a boundary between two different mediums.
Ray Model of LightRay Model of LightReflection:Reflection: Light rays reflect (bounce) off the surface of a
new medium that it encounters in a very predictable fashion.
The “Normal” is a line perpendicular to the surface of the second medium.
1 = 1’
Angle of Incidence (1) = Angle of Reflection (1’)Angles are measured from the Normal.
I = rAlways!!
This law is obviously true in some situations and not so obviously true in other situations.
Light rays reflect from the smooth surface in only one direction because all the Normal lines are parallel to each other. All i are the same All r are the same.Light rays reflect in many directions from a rough surface because each ray encounters the surface with a Normal not parallel to the other Normals.However, for each ray:
i = r
Ray Model of LightRay Model of Light
Refraction:Refraction: The tendency for light ray to bend when traveling from one medium into another medium. Examples:Examples: Rays traveling from:
air to waterair to glasswater to glass
Law of Reflection 1 = 1’v1 = speed of light in air (still approximately 3.0x108m/s)v2 = speed of light in glass
Light takes the quickest path between two points.Only 1 Medium Straight Line Path2 Mediums Encountered Bent Line Path
The bent line path allows light to travel relatively more distance in the medium in which it travels faster and less distance in the slower medium.
Draw how you would travel if you were a lifeguard at point A trying to quickly reach a person at point B.
Sand
Shoreline
Ocean
A
B
Light bends toward the Normal when passing from fast medium to a slow medium…just like the lifeguard.Light bends away from the Normal when passing from a slow to a fast medium…just like you in the ocean if you noticed someone stealing from your possessions on shore.
Your possessions
You
Normal
1
2
Law of RefractionLaw of Refraction
Index of Refraction (n)Index of Refraction (n) =speed of light in vacuumspeed of light in medium
n = cv
Index of Refraction is another physical property of a substance (medium)
n 1 because c v Always!However nair 1.00 (to 3 sig.figs.)
f1 = f2
Waves don’t “pile up” at the boundary.
v1 v2
1 2
The wavelength changes at the boundary.
Law of Refraction (Snell’s Law)Law of Refraction (Snell’s Law)
sin1
sin2
v1
v2
= = constant (for two given mediums)
sin1
sin2
c/n1
c/n2
=
v2 = cn2
v1 = cn1
sin1
sin2
n2
n1
=
n1 sin1 = n2 sin 2 Snell’s Law
ExampleExample (Snell’s Law)
Find the angle (relative to the Normal) of the ray in the water.
Strategy:Strategy:Draw the Normal and measure 1 relative to the normal.Look up n1 and n2
n1 = 1.00 (air)n2 = 1.33 (water)Plug into Snell’s Law and Solve for 2
1.00 sin60 = 1.33 sin2
sin2 = .651 2 = sin-1(.651)2 = 41
1=60air
water
30
41
ExampleExample (Snell’s Law and “Critical Angles”)
Find the “critical angle” where light travels parallel to the surface of the water upon leaving the water.