Conceptual Physical Science

murmerlastΠολεοδομικά Έργα

16 Νοε 2013 (πριν από 3 χρόνια και 11 μήνες)

118 εμφανίσεις

Copyright © 2008 Pearson Education, Inc., publishing as Pearson Addison Wesley

Hewitt/Suchocki/Hewitt


Conceptual Physical Science
Fourth Edition



Chapter 11:

LIGHT

Copyright © 2008 Pearson Education, Inc., publishing as Pearson Addison Wesley

This lecture will help you
understand:


Electromagnetic Spectrum


Transparent and Opaque Materials


Reflection


Refraction


Color


Dispersion


Polarization

Copyright © 2008 Pearson Education, Inc., publishing as Pearson Addison Wesley

Electromagnetic Nature of Light

Light:


electromagnetic waves created by vibrating electric
charges having frequencies that fall within the range of
sight


frequency of vibrating electrons equals the frequency of
the light


travels nearly a million times faster

than sound in air


light and all electromagnetic waves

are transverse waves

Copyright © 2008 Pearson Education, Inc., publishing as Pearson Addison Wesley

Electromagnetic Spectrum

Electromagnetic wave


made up of vibrating electric and magnetic fields
that regenerate each other by electromagnetic
induction






Copyright © 2008 Pearson Education, Inc., publishing as Pearson Addison Wesley

Electromagnetic Spectrum

The Electromagnetic Spectrum

Copyright © 2008 Pearson Education, Inc., publishing as Pearson Addison Wesley

The electromagnetic spectrum spans waves ranging from
lowest to highest frequencies. The smallest portion of the
electromagnetic spectrum is that of

A.

radio waves.

B.
microwaves.


C.
visible light.

D.
gamma rays.


Electromagnetic Spectrum

CHECK YOUR NEIGHBOR


Copyright © 2008 Pearson Education, Inc., publishing as Pearson Addison Wesley

The electromagnetic spectrum spans waves ranging from
lowest to highest frequencies. The smallest portion of the
electromagnetic spectrum is that of

A.

radio waves.

B.
microwaves.


C.
visible light.

D.
gamma rays.



Explanation
:


This can be inferred by a careful study of the spectrum and its
regions in Figure 11.3.

Electromagnetic Spectrum

CHECK YOUR ANSWER

Copyright © 2008 Pearson Education, Inc., publishing as Pearson Addison Wesley

Electromagnetic Nature of Light

Order of increasing frequency of visible light:


red


violet

nearly twice the frequency of red


ultraviolet

cause of sunburns


X
-
rays


gamma rays

Copyright © 2008 Pearson Education, Inc., publishing as Pearson Addison Wesley

A photographer wishes to photograph a
lightning bolt by setting a camera so that it is
triggered by the sound of thunder.


Electromagnetic Nature of Light

A situation to ponder…


Copyright © 2008 Pearson Education, Inc., publishing as Pearson Addison Wesley

Is this a good idea or a poor idea?

A.

Good idea for nearby lightning strikes.

B.
Good idea for all strikes.

C.
Poor idea for nearby lightning strikes.

D.
Poor idea for all strikes.


A situation to ponder…

CHECK YOUR NEIGHBOR

Copyright © 2008 Pearson Education, Inc., publishing as Pearson Addison Wesley

Is this a good idea or a poor idea?

A.

Good idea for nearby lightning strikes.

B.
Good idea for all strikes.

C.
Poor idea for nearby lightning strikes.

D.
Poor idea for all strikes.




Explanation
:


Light travels about a million times faster than sound. By the time
the sound of thunder arrives, the lightning bolt is long gone.

A situation to ponder…

CHECK YOUR ANSWER


Copyright © 2008 Pearson Education, Inc., publishing as Pearson Addison Wesley

Transparent and Opaque Materials

Opaque materials:


colored glass is opaque to much of incident
white light

Copyright © 2008 Pearson Education, Inc., publishing as Pearson Addison Wesley

Transparent and Opaque
Materials

Light incident on:


dry surfaces bounces directly to your eye


wet surfaces bounces inside the transparent wet
region, absorbing energy with each bounce, and
reaches your eye darker than from a dry surface

Copyright © 2008 Pearson Education, Inc., publishing as Pearson Addison Wesley

Transparent and Opaque
Materials

Light is transmitted similar to sound


light incident on matter forces some electrons in matter
to vibrate







Copyright © 2008 Pearson Education, Inc., publishing as Pearson Addison Wesley

Transparent and Opaque
Materials

How light penetrates a pane of glass







electrons in atoms of glass are forced into vibration


energy is momentarily absorbed and vibrates electrons in the
glass


a vibrating electron either emits a photon or transfers the
energy as heat


light slows due to time delay between absorption and
reemission of photons












Copyright © 2008 Pearson Education, Inc., publishing as Pearson Addison Wesley

Transparent and Opaque
Materials

Average speed of light through different
materials


vacuum

c
(300,000,000 m/s)


atmosphere

slightly less than
c

(but rounded off to
c
)


water

0.75
c


glass

0.67
c,

depending on material


diamond

0.41
c

Copyright © 2008 Pearson Education, Inc., publishing as Pearson Addison Wesley

Strictly speaking, the photons of light incident on glass are

A.

also the ones that travel through and exit the other side.

B.
not the ones that travel through and exit the other side.

C.
absorbed and transformed to thermal energy.

D.
diffracted.


Transparent and Opaque Materials

CHECK YOUR NEIGHBOR


Copyright © 2008 Pearson Education, Inc., publishing as Pearson Addison Wesley

Strictly speaking, the photons of light incident on glass are

A.

also the ones that travel through and exit the other side.

B.
not the ones that travel through and exit the other side.


C.
absorbed and transformed to thermal energy.

D.
diffracted.



Explanation
:


Figure 11.6 illustrates this nicely. A photon that exits the glass is
not the same photon that began the process of absorption and re
-
emission.

Transparent and Opaque Materials

CHECK YOUR ANSWER


Copyright © 2008 Pearson Education, Inc., publishing as Pearson Addison Wesley

Reflection

Reflection:


the returning of a wave to the medium through which it
came when encountering a reflective surface

Law of reflection:


angle of incidence = angle of reflection

Copyright © 2008 Pearson Education, Inc., publishing as Pearson Addison Wesley

Reflection

Virtual image


same size as object, formed behind a mirror, and located
at the position where the extended reflected rays
converge



as far behind the mirror as the object is in front of the
mirror





Copyright © 2008 Pearson Education, Inc., publishing as Pearson Addison Wesley

Reflection

Plane mirror


note, the only axis reversed in an image is the
front
-
back axis









Copyright © 2008 Pearson Education, Inc., publishing as Pearson Addison Wesley

Reflection

Curved mirrors form a different virtual image


convex mirror (that curves outward): virtual image is smaller and
closer to the mirror than the object


concave mirror (that curves inward): virtual image is larger and
farther away than the object






Copyright © 2008 Pearson Education, Inc., publishing as Pearson Addison Wesley

Reflection

Diffuse reflection


light striking a rough or irregular surface reflects in many
directions


an undesirable circumstance is the ghost image that
occurs on a non
-
cable TV set when TV signals bounce
off buildings and other obstructions






Copyright © 2008 Pearson Education, Inc., publishing as Pearson Addison Wesley

Diffuse Reflection Application


The open
-
mesh
parabolic dish is a
diffuse reflector for
short
-
wavelength
light.


It is also a polished
reflector for long
-
wavelength radio
waves.

Copyright © 2008 Pearson Education, Inc., publishing as Pearson Addison Wesley

Diffuse Reflection

Different road surfaces determine amount of diffuse
reflection


Rough road surface

diffuse reflection of illumination from your car
headlights lets you see road ahead at night


Wet road surface is smooth

more plane mirror than diffuse, so
seeing road ahead is more difficult


Now you know!



Copyright © 2008 Pearson Education, Inc., publishing as Pearson Addison Wesley

When you stand 2 meters in front of a plane mirror, your
image is

A.

2 meters in back of the mirror.

B.
4 meters from you.


C.
Both A and B.

D.
None of the above.


Reflection

CHECK YOUR NEIGHBOR


Copyright © 2008 Pearson Education, Inc., publishing as Pearson Addison Wesley

When you stand 2 meters in front of a plane mirror, your
image is

A.

2 meters in back of the mirror.

B.
4 meters from you.


C.
Both A and B.

D.
None of the above.


Reflection

CHECK YOUR ANSWER


Copyright © 2008 Pearson Education, Inc., publishing as Pearson Addison Wesley

Refraction

Refraction


bending of light when it passes from one
medium to another


caused by change in speed of light






Copyright © 2008 Pearson Education, Inc., publishing as Pearson Addison Wesley

Refraction

Here we see light rays pass from air into
water and from water into air


pathways are reversible for both reflection and
refraction




Copyright © 2008 Pearson Education, Inc., publishing as Pearson Addison Wesley

Refracted light that bends toward the normal is light that
has

A.

slowed down.

B.
sped up.


C.
nearly been absorbed.

D.
diffracted.

Refraction

CHECK YOUR NEIGHBOR

Copyright © 2008 Pearson Education, Inc., publishing as Pearson Addison Wesley

Refracted light that bends toward the normal is light that
has

A.

slowed down.

B.
sped up.


C.
nearly been absorbed.

D.
diffracted.


Refraction

CHECK YOUR ANSWER

Copyright © 2008 Pearson Education, Inc., publishing as Pearson Addison Wesley

Refracted light that bends away from the normal is light that
has

A.

slowed down.

B.
sped up.


C.
nearly been absorbed.

D.
diffracted.


Refraction

CHECK YOUR NEIGHBOR

Copyright © 2008 Pearson Education, Inc., publishing as Pearson Addison Wesley

Refracted light that bends away from the normal is light that
has

A.

slowed down.

B.
sped up.


C.
nearly been absorbed.

D.
diffracted.



Explanation
:


This question is a consistency check with the question that asks
about light bending toward the normal when slowing.


Refraction

CHECK YOUR ANSWER

Copyright © 2008 Pearson Education, Inc., publishing as Pearson Addison Wesley

Refraction

Illusions caused by refraction









Objects submerged in water appear closer to the
surface.

Copyright © 2008 Pearson Education, Inc., publishing as Pearson Addison Wesley

Refraction

Illusions caused by refraction
(continued)










Objects such as the Sun seen through air are
displaced because of atmospheric refraction.

Copyright © 2008 Pearson Education, Inc., publishing as Pearson Addison Wesley

Refraction

Illusions caused by refraction
(continued)











Atmospheric refraction is the cause of mirages.

Copyright © 2008 Pearson Education, Inc., publishing as Pearson Addison Wesley

Which of these would not exist if light didn’t slow in
transparent materials?

A.

Rainbows.

B.
Mirages.


C.
Magnifying glasses.

D.
All wouldn’t be.




Refraction

CHECK YOUR NEIGHBOR

Copyright © 2008 Pearson Education, Inc., publishing as Pearson Addison Wesley

Which of these would not exist if light didn’t slow in
transparent materials?

A.

Rainbows.

B.
Mirages.


C.
Magnifying glasses.

D.
All wouldn’t be.


Refraction

CHECK YOUR ANSWER

Copyright © 2008 Pearson Education, Inc., publishing as Pearson Addison Wesley

Color

Color we see depends on frequency
of light ranging from lowest (red) to
highest (violet).

In between are colors of the rainbow.


Hues in seven colors: red, orange,
yellow, green, blue, indigo, and violet.

Grouped together, they add to appear
white.

Copyright © 2008 Pearson Education, Inc., publishing as Pearson Addison Wesley

Color

Selective Reflection


Most objects don’t emit light, but reflect light.


A material may absorb some of the light and

reflect the
rest.

Selective Transmission


The color of a transparent object depends on the color of
the light it transmits.

Copyright © 2008 Pearson Education, Inc., publishing as Pearson Addison Wesley

Color

Mixed Color Lights


Three types of cone receptors in our eyes perceive color

each stimulated by only certain frequencies of light:


lower
-
frequency light stimulate cones sensitive to low
frequencies (red)


Middle
-
frequency light stimulate cones sensitive to
mid
-
frequencies (green)


High
-
frequency light stimulate cones sensitive to high
frequencies (blue)


Stimulation of all three cones equally, we see white
light

Copyright © 2008 Pearson Education, Inc., publishing as Pearson Addison Wesley

Color

Additive primary colors (red, blue, green):


red + blue = magenta


red + green = yellow


blue + green = cyan

Copyright © 2008 Pearson Education, Inc., publishing as Pearson Addison Wesley

Color

Opposites of primary colors:


opposite of green is magenta


opposite of red is cyan


opposite of blue is yellow

The addition of any color to its opposite color results in white.

Copyright © 2008 Pearson Education, Inc., publishing as Pearson Addison Wesley

Dispersion

Dispersion


process of separation of light into colors arranged by
frequency













Components of white light are dispersed in a prism (and
also in a diffraction grating)

Copyright © 2008 Pearson Education, Inc., publishing as Pearson Addison Wesley

When white light passes through a prism, green light is
bent more than

A.

blue light.

B.
violet light.


C.
red light.

D.
None of the above.


Dispersion

CHECK YOUR NEIGHBOR


Copyright © 2008 Pearson Education, Inc., publishing as Pearson Addison Wesley

When white light passes through a prism, green light is
bent more than

A.

blue light.

B.
violet light.


C.
red light.

D.
None of the above



Dispersion

CHECK YOUR ANSWER

Copyright © 2008 Pearson Education, Inc., publishing as Pearson Addison Wesley

Dispersion

Rainbows


a colorful example of dispersion












Copyright © 2008 Pearson Education, Inc., publishing as Pearson Addison Wesley

Dispersion

Rainbow detail














Copyright © 2008 Pearson Education, Inc., publishing as Pearson Addison Wesley

Dispersion

Rainbow facts


an observer is in a position to see only a single
color from any one droplet of water


your rainbow is slightly different from the
rainbow seen by others


your rainbow moves with you


disk within the bow is brighter because of
overlapping of multiple refractions (which don’t
occur outside the disk)

Copyright © 2008 Pearson Education, Inc., publishing as Pearson Addison Wesley

Dispersion

Rainbow facts (continued)


secondary rainbow is fainter (due to two internal
reflections and refracted light loss).


secondary bow is reversed in color (due to the extra
internal reflection)








Copyright © 2008 Pearson Education, Inc., publishing as Pearson Addison Wesley

Compared with the primary rainbow, the secondary bow

A.

is dimmer.

B.
has colors reversed.


C.
is caused by two internal reflections.

D.
All of the above.


Dispersion

CHECK YOUR NEIGHBOR

Copyright © 2008 Pearson Education, Inc., publishing as Pearson Addison Wesley

Compared with the primary rainbow, the secondary bow

A.

is dimmer.

B.
has colors reversed.


C.
is caused by two internal reflections.

D.
All of the above.



Dispersion

CHECK YOUR ANSWER

Copyright © 2008 Pearson Education, Inc., publishing as Pearson Addison Wesley

Polarization

Polarization


alignment of transverse electric vectors in
electromagnetic waves


property of transverse waves







Left: E & M wave is polarized Right: rope vibrations are polarized


In both cases, wave is in the same plane as the plane of
vibration
.

Copyright © 2008 Pearson Education, Inc., publishing as Pearson Addison Wesley

Polarization

Unpolarized light


vibrations producing light are in random directions










Copyright © 2008 Pearson Education, Inc., publishing as Pearson Addison Wesley

Polarization

Polarized light










Unpolarized light divided into two internal beams
polarized at right angles to each other. One beam is
absorbed while the other beam is transmitted.

Copyright © 2008 Pearson Education, Inc., publishing as Pearson Addison Wesley

Polarization

Polarized light
(continued)









Use your knowledge of vectors and vector components
to explain how light that can’t pass through a pair of
Polaroids at right angles to each other will pass light
when a third Polaroid is sandwiched between them!

Copyright © 2008 Pearson Education, Inc., publishing as Pearson Addison Wesley

Polarization occurs for waves that are

A.

transverse.

B.
longitudinal.


C.
Both A and B.

D.
Neither A nor B.



Polarization

CHECK YOUR NEIGHBOR

Copyright © 2008 Pearson Education, Inc., publishing as Pearson Addison Wesley

Polarization occurs for waves that are

A.

transverse.

B.
longitudinal.

C.
Both A and B.

D.
Neither A nor B.



Polarization

CHECK YOUR ANSWER