Light and
Optics
IDS Physics: Unit 7, Lecture 1
Nature of Light
What is light?
•
Light is a wave
•
But what is the medium?
•
Applet
Light is also a particle
•
The particle is called a photon.
•
The particle nature of light was first proposed
by Einstein to explain the photoelectric effect.
•
http://phet.colorado.edu/simulations/sims.php?sim=Photoelectric_Effect
Wave Nature of Light
Light is an Electro
-
magnetic wave (EM Wave)
Energy is transferred through the electromagnetic
fields
The Spectrum
Electromagnetic Waves
http://phet.colorado.edu/simulations/sims.php?si
m=Radio_Waves_and_Electromagnetic_Fields
Light
“Light” is the name given to EM waves that have
a frequency detectable by the human eye.
Our eyes are electromagnetic wave detectors.
Infrared Vision
External detectors can
be used to detect other
frequencies
Polarization
The electric field
“wiggles” in a certain
direction.
Polarization
If the wave passes through a constriction, only
the part of the wave that is parallel to the slit will
continue.
Polarization
Polarization
Speed of Light
Light travels so fast it was originally thought to be
instantaneous.
Careful experiments reveal that it has a finite
velocity
8
3.00 10 m/s 186,000 feet/sec
c
Speed of Light
All EM waves travel at this speed in a vacuum.
c
is the absolute speed limit of the universe
In other media, like glass, light will still travel but
with a reduced speed.
Light experiences no acceleration:
x v t
Reflection
A mirror and a piece of white paper both reflect
essentially all light that hits them. What is the
difference?
Reflection
Mirror is example of specular reflection
mirror surface
Reflection
Diffuse reflection from a rough surface
Reflection
Microscopic view of
a sheet of paper
Reflections
Reflection: Headlights
Why do oncoming headlights seem so bright?
Why don’t headlights work in the rain?
Transmission
Light can enter an optically transparent material.
The light slows down as it is absorbed and
emitted by the atoms
Speed of Light
n the called the index of
refraction
it can be thought of as the
“slow down” factor for light
c
n
v
Your Turn: Index of Refraction
When passing though a solid piece of plastic,
light travels at 1.5 x 10
8
m/s. What will be the
index of refraction for this material?
A.
n = 1
B.
n = 1/2
C.
n = 2
D.
n = 3/2
E.
n = 2/3
Index of Refraction
0%
20%
40%
60%
80%
100%
Vacuum
Air
Ice
Water
EtOH
glass
Diamond
Index of Refraction
Material
Index of Refraction
Vacuum
1.000
Air
1.00029
Ice
1.310
Water
1.330
EtOH
1.360
glass
1.520
Diamond
2.417
Refraction
What happens if a wave of light approached an
interface where it must slow down?
Refraction
Refraction
is the bending of a wave when it
travels from one medium to another.
Animation showing how light bends
Refraction Examples
Slice your finger example
The bent straw
Spear fishing
Refraction Examples
Catching fish
n=1
n=1.5
Refraction Terminology
Refraction
Light bends towards the normal when it enters a
material with a slower speed (higher n)
n=1
n=1.5
Refraction
Light bends away the normal when it enters a
material with a higher speed (lower n)
n=1
n=1.5
Refraction of Sound
Dispersion
Each frequency of light has a slightly different
speed in a media
Each color bends a slightly different amount
Dispersion
Dispersion
Dispersion
is the separation of light into colors by
refraction
Animation
Dispersion
Most famous
example of
dispersion is the
rainbow
Rainbow
Rainbow
Total Internal Reflection
Simulator
When going from a slower to a faster medium,
light cannot escape if the angle is too big.
Applications
Diamonds
Applications
Light Pipes
Links
NASA Overview of EM Spectrum
Review of Concepts with lots of graphics
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