Light and Optics

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