Transcript Glencoe Physics Chapter 16

Glencoe Physics
Chapter 16
“Fundamentals of Light”
Characteristics of Light
From our knowledge of waves, we know they vary
in frequency and wavelength. We have also
determined that light has wave and particle
properties. Light is probably our most important
means of learning about the physical nature of our
universe.
 light - that portion of the electromagnetic spectrum
that stimulates the human eye
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The Electromagnetic Spectrum
cosmic high frequency
short wavelength
 gamma
 x ray
 ultraviolet
 visible
 infrared
 microwaves
 radio waves
 electricity low frequency long wavelength
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Optical Terms
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luminous body - an object which emits its own light
Example (sun)
illuminous body - an object which reflects light
Example (moon)
transparent object - allows total light transmission
Example (glass)
translucent object - allows partial transmission
Example (church window)
opaque object - does not allow light transmission
Example (wall)
Speed of Light
Light moves at a speed of over 186,000 miles per
second or 3 X 108m/s.
 If a gun fired a bullet that moved at this speed, how
many trips could it make around the world in one
second?
c=f
 The AM radio band extends from 5.4 X 105 Hz to 1.7
X 106 Hz. What are the longest and shortest
wavelengths in this frequency range?
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Illumination of a Point Source
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Light obeys the inverse square law. If light is emitted
from a point source having an intensity of one candle,
at a distance of 1m, the intensity would be ___ lumen.
At a distance of 2m, the intensity would be ___
lumens. The equation relating light intensity and
distance would be,
I - intensity in cd
E = I / d2
E - illumination in lm
d - distance in m
P438,8-12
Flat Mirrors
Regular reflection enables us to see images of
objects in mirrors.
 Light rays reflect from objects and fall on mirrors
and are reflected in all directions.
 This enables us to see an image of the object in
infinite locations.
 A plane mirror reflects light rays in the same
manner that they approach it.
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Reflection of Light
Reflection of light involves the return of light
waves from an opaque object. This property
enables us to see objects.
 Law of Reflection
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The angle of incidence is equal to the angle of
reflection.
 regular reflection - parallel incident rays are
reflected parallel
 irregular reflection - parallel incident rays are
reflected nonparallel
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The image in a plane mirror is;
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1. upright - not upside down
2. reversed left to right - reflections of others are
reversed
3. the same size - no enlargement or reduction
4. located the same distance behind the mirror as the
object is in front of the mirror - image gets smaller as
you move away
5. virtual - not real, appears to be behind the mirror
Page 463; 6,9,10
Curved Mirrors
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Converging mirrors are also referred to as concave
mirrors.
They may be thought of as an infinite number of plane
mirrors located along a curved path.
The images seen in concave mirrors depends on the
relative distance between the mirror and the object.
There are six different cases of which images can be
generally defined.
To determine these cases, one must be able to draw an
optic diagram which can be used to locate the image.
Draw a concave mirror and label
the following parts.
F - focal point
f - focal length
 C - center of curvature r- radius of curvature
 di - distance to image do- distance to object
 V - vertex
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--------------------------------------------------------axis
Mathematical Relationships
1. radius of curvature - r, focal length - f
 r = 2f
 2. distance to object - do, distance to image - di,
focal length - f
 1/f = 1/di + 1/do
 3. size of object - so, size of image - si, distance
to object - do, distance to image di
 si/so = di/do
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Sample Problems
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A concave mirror has a focal length of 20cm.
Find the radius of curvature of the mirror.
 2. An object is located 36cm from a concave
mirror having a radius of curvature of 24cm.
Locate the image.
 3. The object in problem #2 is 3cm tall. Find
the height of the image.
Six Cases of Images Formed in
Converging Mirrors
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1. Object at infinity, Image is..........
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Six Cases of Images Formed in
Converging Mirrors
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2. Object beyond C, Image is..........
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Six Cases of Images Formed in
Converging Mirrors
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3. Object at C, Image is..........
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Six Cases of Images Formed in
Converging Mirrors
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4. Object between C & F, Image is..........
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Six Cases of Images Formed in
Converging Mirrors
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5. Object at F, Image is..........
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Six Cases of Images Formed in
Converging Mirrors
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6. Object between F & V, Image is..........
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 Assignment:
Page 469; 12-16
Virtual Images Formed by Convex
Mirrors
 Certain
mirrors cause reflected rays to diverge
or propagate in such a manner that they never
cross.
 Another name given to this type of diverging
mirror is a "convex" mirror.
 Uses of diverging mirrors include...
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1. rear view mirrors
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2. supermarket isle mirrors
Draw a diagram of an object located in
front of a diverging mirror.
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--------------------------------------------------------axis
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Image is....
Sample Problem
 An
object is located 20cm from a
diverging mirror of 8cm focal length.
Locate the image.
 The object is 4cm tall. How tall is the
image?
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Assignment: Page 472; 17-21
Color and Polarization
 Color
is a property of light which is a
result of varying frequency. The
wavelength is also used to distinguish
colors. The range of visible light for
wavelength is 400nm for violet to
700nm for red.
Polarization of Light
→
Polarization Photography
Reduce Sun Glare
Reduce Reflections
Darkens Sky
Increase Color Saturation
Reduce Haze
Polarization Photography
Without Polarizer
With Polarizer
• Provides better Color Saturation
• Darkens the sky
Polarization Photography
Without Polarizer
With Polarizer
Polarization Photography : Scattering
Haze
De-hazed
Polarization Photography : Wide Angle Lenses
Vignetting of the Sky
Polarization Photography : Reflections
Reduce Reflections
Polarization Photography : Reflections
Reduce Reflections
Polarization Photography : Reflections
Many titled planes
Aqua-polaricam
Polarization Photography : Underwater
• Offshore structures
• Offshore drilling rigs
• Vessel inspection
• Underwater ROV/AOV
• Marine biology
• Recreational photography
• Marine archaeology
• Underwater pipelines
and communication
Birefrengence
Interference pattern due to different refractive indices
Light as Plane Waves
I max
•Sinusoidal plane waves very
good approximation.
•Very useful for characterizing
polarization.
I min
max
180 o
•Polarized Wave: Has only one preferred orientation.
•Un-polarized Wave: Has no preferred orientation.
or has all orientations.
•Partially polarized wave: Has preferred orientation but
has energy in other orientations as well.
Classification of Polarization
Linear : Two orthogonal plane waves with same phase but
possibly different amplitudes.
Circular: Two orthogonal plane waves with 90 deg phase
shift but same amplitudes.
Elliptical: Possibly any degree phase shift with
different amplitudes.
Linear Polarization
Circular Polarization
Elliptical Polarization
Crossed Polarizers
Polarizer Puzzle
If crossed polarizers block all light, why does putting a third polarizer at 45°
between them result in some transmission of light?
Law of Malus
Amplitude:
Intensity = Const . (Amplitude)^2
Polarized Sunglasses
Reduce glare off the roads while driving
Frequently Asked Questions
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Why is a red shirt red?
Most of us know that red shirts are red because they
reflect red light and absorb other frequencies.
Why is black clothing warmer that white clothing?
Black absorbs all frequencies.
Why do cars get hot in the summer when the windows are
rolled up?
Visible light passes through the glass and strikes the
interior which interferes with the frequencies and
converts the light to infrared, heat, which will not pass
through the glass.