The most famous and accurate
1880
Michelson’s results
C = 186,282.3960 miles per second,
plus or minus 3.6 feet per sec.
C = 299,792.4562 kilometers per second,
plus or minus 1.1 meters per second
The Speed of Light
 The speed of light in a vacuum is a
universal constant
 Accepted values 3.00 x 108 m/s
or 186,000 mi/s
 A beam of light could travel around
the earth, it would make 7.5 trips in
one second.
 The distance light travels in one
year is called a light-year.
Electromagnetic Waves
 Light is energy that is emitted by
accelerating electric charges—often
electrons in atoms.
 This energy travels in a wave that is
partly electric and partly magnetic.
 Such a wave is an electromagnetic
wave.
 Light is a small portion of the broad
family of electromagnetic waves
Electromagnetic Waves
This list includes in order of increasing (f) :
radio waves, microwaves, infrared waves,
visible light waves, ultraviolet waves, X rays, and
gamma waves
Electromagnetic Waves
POP QUIZ
 QUESTION:
 Is it correct to say that a radio wave is a low-frequency light
wave? Is a radio wave also a sound wave?
ANSWER:
 Both a radio wave and light wave are electromagnetic waves
originating from the vibrations of electrons. Radio waves have
lower frequencies of vibration than a light wave, so a radio
wave may be considered to be a low-frequency light wave. A
sound wave is a mechanical vibration of matter and is not
electromagnetic. A radio wave is not a sound wave.
Electromagnetic Waves
 The range of electromagnetic waves, or the electromagnetic
spectrum
 The lowest frequency of light we see in our eyes appears red
 The highest frequency of light we see in our eyes appears
violet
 Electromagnetic waves of frequencies lower than the red of
visible light are called infrared
 Electromagnetic waves of frequencies higher than those of
violet are called ultraviolet
Light and Transparent Materials
 Light is energy carried in an
electromagnetic wave
 Light incident upon matter, forces
electrons to vibrate
 How a receiving material responds
when light is incident upon it
depends on the frequency of light
and the natural frequency of
electrons in the material
Propagation
The natural vibration frequencies of an electron depend
on how strongly it is attached to a nearby nucleus
Different materials have different electric “spring
strengths.”
Light and Transparent Materials
The energy of vibrating electrons is reemitted as
transmitted light.
The (f) of the reemitted light = (f) incident light
A slight time delay occurs between absorption and
reemission.
There is lower average speed of light through a
transparent material.
Light and Transparent Materials
The Secret of the Archer Fish
 Light travels at different average speeds
through different materials.
 Light travels slightly more slowly in water
than in the atmosphere, but its speed there
is usually rounded off to c.
 When light emerges from these materials
into the air, it travels at its original speed,
c.
 Glass is transparent to visible light, but not
Light is not
to ultraviolet and infrared light.
changed because of
the perpendicular
Opaque Materials
 Most materials absorb light without reemission and
thus allow no light through them; they are opaque.
 In opaque materials, any coordinated vibrations
given by light to the atoms and molecules are
turned into random kinetic energy—that is, heat
Why are metals Shiny?
 Metals are also opaque.
 When light shines on metal and sets these free
electrons into vibration, their energy does not
“spring” from atom to atom in the material, but is
reemitted as visible light.
 This reemitted light is seen as a reflection and that is
why metals are shiny.
Opaque Materials
Our atmosphere is
transparent to visible light
and some infrared, but
almost opaque to highfrequency ultraviolet waves.
The small amount of
ultraviolet that does get
through is responsible for
sunburns.
Polarization
Unpolarized light
A light wave which is vibrating in more
than one plane
Polarized light
are light waves in which the
vibrations occur in a single plane
EX: Light emitted by the sun,
by a lamp in the classroom, or
by a candle flame
Polarization
 Polarization explains why light waves
are transverse and not longitudinal
 A single vibrating electron emits an
electromagnetic wave that is
polarized.
 A vertically vibrating electron emits
light that is vertically polarized,
 A horizontally vibrating electron emits
light that is horizontally polarized.
Polarization
More Polarization
Polarization Quiz
What is the result of shining light through two polarizing
filters whose transmission axes are parallel to each other
The first filter will polarize the light, blocking half of its
vibrations. The second filter will have no effect.
Which of the three pairs of sunglasses
to the right would be best for blocking
road glare?
A. The light coming from the road will
have a slight vertical polarization
.
Lumination
 Luminous objects
 are objects which generate their own light
Illumination
 Illuminated objects
 are objects which are capable
of reflecting light to our eyes
 None of us are light-generating objects
 It is only by reflection that we, see
Reflection
 Reflection: when a wave reaches a boundary,
some or all of it bounces back into the first
medium
 Totally Reflected waves are reflected back
rather than transmitted into another object
 Partially Reflected some energy is transmitted
into a new medium
Reflection
 Luminous objects emit light in a variety of
directions
 your eye only sees the very small portion of
rays coming towards it
 Ray = a narrow beam of light
The Law of Reflection
 angle of incidence = The angle made by the
incident ray and the normal
 angle of reflection = The angle made by the
reflected ray and the normal
 Normal = imaginary line drawn perpendicular
to the surface
The Law of Reflection
 angle of incidence = angle of reflection
The Law of Reflection
 Reflected waves travel back to the
medium from whence they came
 Incident rays and reflected rays make
equal angles with the normal
The Law of Reflection
Do Now Problems
.
1. Differentiate between the angle of
incidence and the angle of reflection
2. What is meant by the normal to the
surface?
3. What is the law of reflection
Pop Quiz
1. Consider the diagram at the
right. Which one of the angles (A,
B, C, or D) is the angle of
incidence? Which one of the angles
is the angle of reflection?
2. A ray of light is incident
towards a plane mirror at an
angle of 30-degrees with the
mirror surface. What will be the
angle of reflection?
60 degrees. Note the angle
of incidence is not 30
degrees!
Mirrors
 light reflects off surfaces in a very predictable
manner - law of reflection
 Rays of light are reflected from mirrors in all
directions
The Law of Reflection is Always Observed
(regardless of the orientation of the surface)
Mirrors
are images which are formed in
locations where light does not actually reach
 Virtual images
are formed through reflection
that can be seen by an observer but can not
be projected on a screen
 Virtual Image
 light from the object does not actually come
to a focus
Mirrors
 Your eyes cannot differentiate between a
real image and a virtual one
Your image in a plane mirror is?
ALWAYS
VIRTUAL !!!
Refraction of Light
• The bending of the path of light
• Refraction occurs as light passes across the
boundary between two medium
• A synonym for refraction is
"bending”
Refraction
 The change in speed that occurs at an interface or
boundary between two different media
Refraction of Light
• The speed of a light wave is dependent
upon the optical density of the material
through which it moves
Refraction
 The optical density of a material relates to
the tendency of the atoms of a material to
maintain the absorbed energy of an
electromagnetic wave

 One indicator of the optical density of a
material is the
index of refraction value
Refraction of Light
 When light rays enter a medium in which
their speed increases (less dense) the rays
bend away from the normal.
SFA = Slow to Fast, Away From Normal
If a ray of light passes across the boundary
from a material in which it travels slowly into a
material in which travels faster, then the light
ray will bend away from the normal line
Refraction of Light
When light rays enter a medium in which
their speed decreases (more dense) the
rays bend toward the normal
FST = Fast to Slow, Towards Normal
If a ray of light passes across the boundary
from a material in which it travels fast into a
material in which travels slower, then the light
ray will bend towards the normal
Refraction of Light
 How does refraction causes the bottom of a
clear lake or pool to appear?
CLOSER !!!!
Refraction of Light
Which medium is more dense?
Refraction of Light
This is caused by
the change in
speed of light as it
passes from one
medium to another
How many times is
the light refracted in
the picture?
Refraction of Light
 The wave speed is always greatest in
the least dense medium
 The wavelength is always greatest in
the least dense medium
Refraction of Light
 The frequency of a wave is not altered
by crossing a boundary
 However, both the wave speed and the
wavelength are changed
Refraction
 INDEX OF REFRACTION
(n)
 Defined as the ratio of the speed of light in
vacuum to the speed of light in the medium
 index of refraction
:
n=c/v
 The speed of light in a given material is related to
this quantity
Every substance has its own specific
index of refraction.
The next slide has a few examples
Material
Index of Refraction
Vacuum
1.0000
Air
1.0003
Ice
1.31
Water
1.333
Ethyl Alcohol
1.36
Plexiglas
1.51
Crown Glass
1.52
Light Flint Glass
1.58
Dense Flint Glass
1.66
Zircon
1.923
Diamond
2.417
Rutile
2.907
Gallium phosphide
3.50
<--lowest optical density
<--highest optical density
 Index of refraction values (represented by the
symbol
(n)
 It is the number of times slower that a light wave would
be in that material
 A vacuum is given an
v =c/
n
(n) value of 1.0000
n =c/
v
Snell’s Law
 Snell's Law
 The relationship between the angles of incidence and
refraction and the indices of refraction of two media
ni sin θi = nr sin θr
Snell’s Law
light crosses a boundary
into a medium with a
higher index of
refraction, the light
bends towards the normal
Light traveling across a
boundary from higher
(n) to lower (n) will
bend away from the
normal
Snell’s Law
 Index of refraction ( n ) = c / v material
 Describes the extent to which the speed of light in
a material medium differs from that in a vacuum
 ni sin i = nr sin r
 ni = index of refraction of incidence material
 i = angle of incidence
 nr = index of refraction of refractive material
 r = angle of refraction
Find the angle of refraction
ni sin i = nr sin r
r = 32o
ni sin i = nr sin r
r = 35o