# Reflection and refraction by HC120426013859

VIEWS: 42 PAGES: 110

• pg 1
```									Reflection and
Refraction
Reflection
Most objects we see reflect light
rather than emit their own light.
Principle of Least Time
• Fermat's principle - light travels in straight
lines and will take the path of least time to
strike mirror and reflect from point A to B
A                                                B

Wrong Path
True Path

MIRROR
Law of Reflection
“The angle of incidence equals the
angle of reflection.”

This is true for both flat mirrors and
curved mirrors.
Normal Line

A    Angle of       Angle of     B
Incidence   =   Reflection

MIRROR
Tangent
Incidence
Normal
Reflection

C            F
Types of Reflection
Specular Reflection - images seen on smooth
surfaces (e.g. plane mirrors)

Diffuse Reflection - diffuse light coming from
a rough surface (cannot see a reflection of
yourself)
Locating the Image for
Plane Mirrors
1. Draw the image the same distance behind
the mirror as the object is in front.
2. Draw a connector line from each object to
each image.
3. If the connector line passes through the
mirror, the image will be seen.
Mirror Images
A   B       C              D              E

These lines are
pointed to the only
images that will be
seen from each of
the original
locations (A-E)
NOTE: No
images will be
seen from E

A   B       C              D              E
Concave Mirrors
Light from Infinite Distance

Focuses at
the focal
C        F             point
Two Rules for Locating the
Image for Concave Mirrors
• Any incident ray traveling parallel to
the principal axis on the way to the
mirror will pass through the focal
point upon reflection
C   F
Two Rules for Concave Mirrors
• Any incident ray traveling parallel to
the principal axis on the way to the
mirror will pass through the focal
point upon reflection

• Any incident ray passing through the
focal point on the way to the mirror will
travel parallel to the principal axis upon
reflection
C   F
C   F
C   F
Virtual
Image

C   F
Mirror Equations
C   F
Mirror Equation: do> C
f = 2 cm, C = 4 cm, ho = 2 cm, do = 5cm, di = ?
1/f = 1/do + 1/di
1/2 = 1/5 + 1/di
1/di = 1/2 - 1/5 = 0.5 – 0.2 = 0.3
di = 3.33 cm
M = hi/ho = -di/do  (-ho x di )/ do = hi
hi = (-2 x 3.3)/5
hi = -1.3 cm
M = - di / do = -0.66
C   F
C   F
Mirror Equation: C >do>f
f = 2 cm, C = 4 cm, ho = 2 cm, do = 3 cm, di = ?
1/f = 1/do + 1/di
1/2 = 1/3 + 1/di
1/di = 1/2 - 1/3 = 0.5 – 0.333 = 0.167
di = 6.0 cm
M = hi/ho = -di/do  (-ho x di )/ do = hi
hi = (-2 x 6)/3
hi = -4.0
M = - di / do = -2.0
C   F
C   F
Mirror Equation: do = f
f = 2 cm, C = 4 cm, ho = 2 cm, do = 2 cm, di = ?
1/f = 1/do + 1/di
1/2 = 1/2 + 1/di
1/di = 1/2 - 1/2 = 0.5 – 0.5 = 0
di =  no image
C   F
Virtual
Image

C   F
Mirror Equation: do < f
f = 2 cm, C = 4 cm, ho = 2 cm, do = 1 cm, di = ?
1/f = 1/do + 1/di
1/2 = 1/1 + 1/di
1/di = 1/2 - 1/1 = 0.5 – 1.0 = -0.5
di = -2.0 cm
M = hi/ho = -di/do  (-ho x di )/ do = hi
hi = (-2 x -2)/1
hi = +4.0
M = - di / do = 2.0
Virtual
Image

C   F
Real vs. Virtual Image
• When a real image is formed, it still
appears to an observer as though light is
diverging from the real image location
– only in the case of a real image, light is
actually passing through the image location
• Light does not actually pass through the
virtual image location
– it only appears to an observer as though the
light was emanating from the virtual image
location
Real Image

C       F

Virtual
Image

C       F
Will an image ever
focus at a single
point with a
convex mirror?

F

Therefore, the
images you see
are virtual!
Refraction
Refraction is the bending of light
when it passes from one transparent
medium to another

This bending is caused by
differences in the speed of light in
the media
Normal
Line

Less Dense

More Dense
Light Beam          Normal
Line #1

Fast

AIR

Slow
WATER

AIR
Normal
Line

More Dense

Less Dense
Light Beam          Normal
Line #1

Fast

AIR

Slow
WATER

AIR
Fast

Normal
Line #2
Refraction Examples
• Light slows down when it goes from air into
water and bends toward the normal.
• An Analogy: A car slows down when it
goes from pavement onto gravel and turns
toward the normal.
• An Illusion : Fish in the water appear closer
and nearer the surface.
http://cougar.slvhs.slv.k12.ca.us/~pboomer/physicslectures/secondsemester/light/refraction/refraction.html
Refraction
Observer

AIR

WATER
False Fish

True Fish
Atmospheric Refraction

Our atmosphere can
bend light and create
distorted images called
mirages.
Index of Refraction Equations
• n = c/v = speed of light in a vacuum
speed of light in medium
Index of Refraction Problem
What is the speed of light in water, which has
an index of refraction of 1.33?

n = c/v  v = c/n

v = (2.998 x 108 m/s) / 1.33

V = 2.25 x 108 m/s
Index of Refraction Equations
• n = c/v = speed of light in a vacuum
speed of light in medium

• n = sin i/sin r
Index of Refraction Problem
A ray of light enters a piece of crown glass at
an angle of 57o and is refracted to 31o inside
the glass. What is the index of refraction?
n = sin i/sin r
= sin 57o / sin 31o
= 1.63
Index of Refraction Equations
• n = c/v = speed of light in a vacuum
speed of light in medium
• n = sin i/sin r

• sin A / sin B = nB / nA
Index of Refraction Problem
A diamond (n = 2.42) is in water (n = 1.33)
and a ray of light shines on it making an
angle of incidence of 55o. What is the
angle of refraction inside the diamond?

sin A / sin B = nB / nA

sin 55o / sin B = 2.42/1.33

B = 27o
Lenses
• Work due to change of direction of light due to
refraction
• Diverging Lens
• A lens that is thinner in the middle than at
the edges, causing parallel light rays to
diverge.
• Converging Lens
• A lens that is thicker in the middle and
refracts parallel light rays passing through
to a focus.
Diverging or
Concave Lens

C          F   F   C
Converging or
Convex Lens

C   F   F          C
Converging or
Convex Lens
Converging or
Convex Lens

C       F   F   C
Converging
or Convex
Lens

C   F   F       C
Lens Equation: do> C
f = 2 cm, C = 4 cm, ho = 2 cm, do = 5cm, di = ?
1/f = 1/do + 1/di
1/2 = 1/5 + 1/di
1/di = 1/2 - 1/5 = 0.5 – 0.2 = 0.3
di = 3.33 cm
M = hi/ho = -di/do  (-ho x di )/ do = hi
hi = (-2 x 3.3)/5
hi = -1.3 cm
Converging
or Convex
Lens

C   F   F       C
Converging
or Convex
Lens

C   F   F       C
Converging
or Convex
Lens

C   F   F       C
Converging
or Convex
Lens

C   F   F       C
Converging
or Convex
Lens

C   F   F      C
Mirror Equation: do < f
f = 2 cm, C = 4 cm, ho = 2 cm, do = 0.5 cm, di = ?
1/f = 1/do + 1/di
1/2 = 1/1 + 1/di
1/di = 1/2 - 1/0.5 = 0.5 – 2.0 = -1.5
di = -.67 cm
M = hi/ho = -di/do  (-ho x di )/ do = hi
hi = (-2 x -.67)/0.5
hi = +8/3 = +3.67
M = - di / do = +1.33
Converging
or Convex
Lens

C   F   F      C
Total Internal Reflection...
…is the total reflection of light
traveling in a medium when it strikes
a surface of a less dense medium

sin θ = n2/n1
http://cougar.slvhs.slv.k12.ca.us/~pboomer/physicslectures/secondsemester/light/refraction/refraction.html
Air – Water Interface
sin θ = n2/n1
Air nair = 1 and Water n2 = 1.33
sin θ = 1.00/1.33 = 0.750
sin θ = 0.750
θ = sin-1 0.750
θ = 49o
Refraction

Critical Angle                        AIR

WATER
49

Total                            Light
Internal                          Source
Reflection
What Is Fiber Optics ?
• Transmitting
communications signals
over hair thin strands
of glass or plastic
• Not a "new" technology
• Concept a century old
• Used commercially for
last 25 years
Fiber Optics Association
Fiber Has More Capacity

This single fiber
can carry more
communications
than the giant
copper cable!

Fiber Optics Association
Fiber Optic Communications
• Applications include
– Telephones
– Internet
– LANs - local area networks
– CATV - for video, voice and Internet
connections
– Utilities - management of power grid
– Security - closed-circuit TV and intrusion
sensors
– Military - everywhere!
Fiber Optics Association
Why Use Fiber Optics?
•   Economics
•   Speed
•   Distance
•   Weight/size
•   Freedom from interference
•   Electrical isolation
•   Security
Fiber Optics Association
Fiber Optic Applications
• Fiber is already used in:
– > 90% of all long distance telephony
– > 50% of all local telephony
– Most CATV networks
– Most LAN (computer network)
backbones

Fiber Optics Association
Fiber Optic Applications
• Fiber is the least expensive, most
reliable method for high speed and/or
long distance communications
• While we already transmit signals at
Gigabits per second speeds, we have
only started to utilize the potential
bandwidth of fiber
Fiber Optics Association
Fiber Technology

Fiber Optics Association
Fiber Technology

Fiber Optics Association
Light Used In Fiber Optics
Fiber optic systems transmit using
infrared light, invisible to the human
eye, because it goes further in the
optical fiber at those wavelengths.

Fiber Optics Association
Wavelength-Division Multiplexing

Fiber Optics Association
Fiber Optic Cable

• Protects the fibers
wherever they are
installed
• May have 1 to over
1000 fibers

Fiber Optics Association
Fiber Optic Connectors
• Terminates the fibers
• Connects to other fibers or
transmission equipment
Medical Fiberscopes
a role in medicine for decades
• Particularly interesting is the ability
to gain information without invasive
procedures
• Using fiber optics in medicine has
opened up new uses for lasers
Fiberscope
Construction
• Fiberscopes were the first use of optical fibers in
medicine
• Invented in 1957
• The objective lens forms a real image on the end of the
bundle of fiber optics
• This image is carried to the other end of the bundle
where an eyepiece is used to magnify the image
Endoscopes
• An endoscope is a fiberscope with
illuminating and viewing fibers
• The uses of these extra channels may
include
– Introducing or withdrawing fluids
– Vacuum suction
– Scalpels for cutter or lasers for surgical
applications
Air – Diamond Interface
sin θ = n2/n1
Air nair = 1 and Diamond n2 = 2.42
sin θ = 1.00/2.42 = 0.413
sin θ = 0.413
θ = sin-1 0.413
θ = 24o
http://cougar.slvhs.slv.k12.ca.us/~pboomer/physicslectures/secondsemester/light/refraction/refraction.html
Dispersion...
• …is the separation of white light into pure
colors (ROY G. BIV).
• The index of refraction is higher for higher
frequencies, so violet is bent the most
• Dispersion Examples:
• Prisms
• Diffraction Gratings
• CD’s
• Raindrops
Rainbows
• Raindrops refract, reflect and disperse sunlight.

• Rainbows will always appear opposite of the
Sun in the sky.

• You cannot run from or run to a rainbow!
Polarization
• Unpolarized light has random directions of
the electric field vector
• Light can be polarized by:
– (1) passing light though a polarizer
material or
– (2) reflecting light off of a solid or liquid
surface.
• For example, reflected light from a lake is
mostly horizontally polarized.
Polarization of Light Waves

• Each atom produces a wave with
its own orientation of E
• All directions of the electric field
vector are equally possible and lie
in a plane perpendicular to the
direction of propagation
• This is an unpolarized wave          General Physics
Polarization of Light, cont
• A wave is said to be linearly
polarized if the resultant electric
field vibrates in the same
direction at all times at a
particular point
• Polarization can be obtained
from an unpolarized beam by
– Selective absorption
– Reflection
– Scattering
General Physics
Polarization by Selective Absorption
• E. H. Land discovered a material that
polarizes light through selective
absorption
– He called the material Polaroid
– The molecules readily absorb light
whose electric field vector is parallel
to their lengths and transmit light
whose electric field vector is
perpendicular to their lengths
General Physics
Selective Absorption, cont

• The most common technique for polarizing light
• Uses a material that transmits waves whose electric field
vectors in the plane are parallel to a certain direction and
absorbs waves whose electric field vectors are
perpendicular to that direction
General Physics
Polarization by Reflection
• When an unpolarized light beam is reflected from a
surface, the reflected light is
– Completely polarized
– Partially polarized
– Unpolarized
• It depends on the angle of incidence
– If the angle is 0° or 90°, the reflected beam is
unpolarized
– For angles between this, there is some degree of
polarization
– For one particular angle, the beam is completely
polarized                          General Physics
Polarization by Reflection, cont
• The angle of incidence for
which the reflected beam
is completely polarized is
called the polarizing
angle, θp
• Brewster’s Law relates the
polarizing angle to the
index of refraction for the
material
sin p
• θp may also be called       n          tan p
Brewster’s Angle               cos  p

General Physics

```
To top