Chapter 22 Properties of Light. Section 1: Objectives Describe light as an electromagnetic wave....
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Chapter 22 Properties of Light
Chapter 22 Properties of Light. Section 1: Objectives Describe light as an electromagnetic wave. Calculate distances traveled by light by using the speed
Section 1: Objectives Describe light as an electromagnetic
wave. Calculate distances traveled by light by using the speed of
light. Explain why light from the sun is important.
Slide 3
Light: An Electromagnetic Wave Light is a type of energy that
travels as a wave. But unlike most other types of waves, light does
not require matter through which to travel. Light is an
electromagnetic wave (EM wave). An electromagnetic wave is a wave
that consists of electric and magnetic fields that vibrate at right
angles to each other.
Slide 4
Figure 1: Electromagnetic Waves
Slide 5
Light: An Electromagnetic Wave An electric field surrounds
every charged object. You see the effect of electric fields
whenever you see objects stuck together by static electricity. A
magnetic field surrounds every magnet. Because of magnetic fields,
paper clips and iron filings are pulled toward magnets.
Slide 6
Light: An Electromagnetic Wave An EM wave can be produced by
the vibration of an electrically charged particle. This vibration
makes electric and magnetic fields vibrate also. Together, the
vibrating fields are an EM wave that carries energy. The transfer
of energy as electromagnetic waves is called radiation.
Slide 7
Light: An Electromagnetic Wave Scientists have yet to discover
anything that travels faster than light. In the near vacuum of
space, the speed of light is about 300,000 km/s. Light travels
slightly slower in air, glass, and other types of matter.
Slide 8
Calculating Speed
Slide 9
Example # 1 The distance from the sun to Venus is 108,000,000
km. Calculate the amount of time it takes for light to travel that
distance. Speed = Distance / Time Speed of light = 300,000
km/s
Slide 10
Example # 2 The distance from the sun to Mercury is 83,000,000
km. Calculate the amount of time it takes for light to travel that
distance. Speed = Distance / Time Speed of light = 300,000
km/s
Slide 11
Light: An Electromagnetic Wave EM waves from the sun are the
major source of energy on Earth. For example, plants use
photosynthesis to store energy from the sun. Animals use and store
energy by eating plants or by eating other animals that eat
plants.
Slide 12
Light: An Electromagnetic Wave Even fossil fuels store energy
from the sun. Fossil fuels are formed from the remains of plants
and animals that lived millions of years ago. Only a very small
part of the total energy given off by the sun reaches Earth. The
sun gives off energy as EM waves in all directions. Most of this
energy travels away in space.
Slide 13
Chapter 22 Section 1 Recap 1) In what for of energy does light
travel? 2) How does light differ from other types of waves? 3) What
type of wave is light? 4) What is the difference between an
electric and magnetic field? 5) List 1 example of how you can
observe an electric field.
Slide 14
Chapter 22 Section 1 Recap 6) How can an EM wave be produced?
7) What 2 vibrating fields make up an EM wave? 8) ___________ is
the speed of light. 9) What is the major source of energy for the
sun? 10) List 1 way animals get energy indirectly from the
sun.
Slide 15
Chapter 22 Section 1 Recap 11) How are fossil fuels formed? 12)
In which direction do EM waves travel away from the sun? 13) From
Figure 1, where is the electric field located in relation to the
magnetic field? 14) From Figure 1, does the magnetic field vibrate
vertically or horizontally? 15) From Figure 1, does the electric
field vibrate vertically or horizontally?
Slide 16
Chapter 22 Section 1 Recap 16) Calculate the time it takes for
light to travel between 2 objects which are 912 km apart. 17)
Calculate the time it takes for light 2 travel between 2 mountain
ranges which are 233.1 km apart. 18) Calculate the time it takes
for light to travel between 2 vehicles which are 155.1 km
apart.
Slide 17
Section 2: Objectives Identify how electromagnetic waves differ
from each other. Describe some uses for radio waves and microwaves.
List examples of how infrared waves and visible light are important
in your life. Explain how ultraviolet light, X rays, and gamma rays
can be both helpful and harmful.
Slide 18
Characteristics of EM Waves The light that you can see is
called visible light. However, there is light that you cant see.
The light that you can see and light that you cannot are both kinds
of electromagnetic (EM) waves. Other kinds of EM waves include X
rays, radio waves, and microwaves. All EM waves travel at 300,000
km/s in a vacuum.
Slide 19
Characteristics of EM Waves The entire range of EM waves is
called the electromagnetic spectrum. The electromagnetic spectrum
is divided into regions according to the length of the waves. The
electromagnetic spectrum is shown on the next slide.
Slide 20
The EM Spectrum: Figure 1
Slide 21
Characteristics of EM Waves Radio waves cover a wide range of
waves in the EM spectrum. Radio waves have some of the longest
wavelengths and the lowest frequencies of all EM waves. Radio waves
are any EM waves that have wavelengths longer than 30 cm. Radio
waves are used for broadcasting radio signals.
Slide 22
Characteristics of EM Waves Radio stations can encode sound
information into radio waves by varying either the waves amplitude
or frequency. Changing amplitude or frequency of a wave is called
modulation. AM stands for amplitude modulation, and FM stands for
frequency modulation.
Slide 23
Characteristics of EM Waves AM radio waves have longer
wavelengths than FM radio waves. AM radio waves can bounce off the
atmosphere and thus can travel farther than FM radio waves. But FM
radio waves are less affected by electrical noise than AM radio
waves, so music broadcast from FM sounds better than music from AM
stations.
Slide 24
Characteristics of EM Waves TV signals are also carried by
radio waves. Most TV stations broadcast radio waves that have
shorter wavelengths and higher frequencies than those from radio
stations. Some waves carrying TV signals are transmitted to
artificial satellites orbiting Earth. The waves are amplified and
sent to ground antennas. The signals then travel through cables to
TVs in homes.
Slide 25
Characteristics of EM Waves Microwaves have shorter wavelengths
and higher frequencies than radio waves. Microwaves have
wavelengths between 1 mm and 30 cm.
Slide 26
Microwaves: Figure 2
Slide 27
Characteristics of EM Waves Microwaves are used to send
information over long distances. Cell phones send and receive
signals using microwaves. Signals sent between Earth and artificial
satellites in space are also carried by microwaves.
Slide 28
Characteristics of EM Waves Microwaves are used in radar. Radar
(radio detection and ranging) is used to detect the speed and
location of objects. Radar sends out microwaves that reflect off an
object and return to the transmitter. The reflected waves are used
to calculate speed.
Slide 29
Characteristics of EM Waves Infrared waves have shorter
wavelengths and higher frequencies than microwaves. The wavelengths
of infrared waves vary between 700 nanometers (nm) and 1 mm. Almost
everything give off infrared waves, including the sun, buildings,
trees, and your body. The amount of infrared waves an object emits
depends on the objects temperature. Warmer objects give off more
infrared waves than cooler objects.
Slide 30
Characteristics of EM Waves Visible light is the very narrow
range of wavelengths and frequencies in the EM spectrum that humans
eyes respond to. Visible light waves have wavelengths between 400
nm and 700 nm. The visible light from the sun is white light. White
light is visible light of all wavelengths combined.
Slide 31
Characteristics of EM Waves Humans see different wavelengths of
visible light as different colors. The longest wave-lengths are
seen as red light. The shortest wave-lengths are seen as violet
light. The range of colors is called the visible spectrum.
Slide 32
Characteristics of EM Waves Ultraviolet light (UV light) is
another type of EM wave produced by the sun. Ultraviolet waves have
shorter wavelengths and higher frequencies than visible light. The
wavelengths of UV light wave vary between 60 nm and 400 nm.
Slide 33
Characteristics of EM Waves Too much UV light can cause
sunburn. UV light can also cause skin cancer and wrinkles, and
damage the eyes. Ultraviolet waves produced by UV lamps are used to
kill bacteria on food and surgical tools. Small amounts of UV light
are beneficial to your body, causing skin cells to produce vitamin
D.
Slide 34
Characteristics of EM Waves X Rays have wavelengths between
0.001 nm and 60 nm. X rays can pass through many materials, making
them useful in the medical field. However, too much exposure to X
rays can damage or kill living cells.
Slide 35
X-Rays: Figure 3
Slide 36
Characteristics of EM Waves Gamma Rays have wavelengths shorter
than 0.1 nm. They can penetrate most materials easily. Gammas rays
are used to treat some forms of cancer. Doctors focus the rays on
tumors inside the body to kill the cancer cells. Gamma rays are
also used to kill harmful bacteria in foods, such as meat and fresh
fruits.
Slide 37
Chapter 22 Section 2 Recap 1) What type of wave is visible
light? 2) What type of wave is non-visible light? 3) How is the EM
spectrum divided into regions? 4)From Figure 1, which type of wave
has the lowest frequency? 5) From Figure 1, which type of wave has
the lowest wavelength?
Slide 38
Chapter 22 Section 2 Recap 6) From Figure 1, which type of wave
has the highest wavelength? 7) From Figure 1, which type of wave
has the highest frequency? 8) What is modulation? 9) What do AM and
FM stand for? 10) Why do AM waves travel farther than FM
waves?
Slide 39
Chapter 22 Section 2 Recap 11) Which type of waves carry TV
signals? 12) From Figure 2, what is a magnetron? 13) What 2 things
are radars used to detect? 14) What does the amount of infrared
waves an object emits depend on? 15) List 1 example of an object
that emits white light.
Slide 40
Chapter 22 Section 2 Recap 16) What is white light? 17) Where
are the longest wavelengths seen? 18) Where are the shortest
wavelengths seen? 19) What is the visible spectrum? 20) Which type
of rays are used to kill harmful bacteria in food and can penetrate
most materials easily?
Slide 41
Section 3: Objectives Describe how reflection allows you to see
things. Describe absorption and scattering. Explain how refraction
can create optical illusions and separate white light into
colors.
Slide 42
Section 3: Objectives Explain the relationship between
diffraction and wavelength. Compare constructive and destructive
interference of light.
Slide 43
Reflection, Refraction, and Interference Reflection happens
when light waves bounce off an object. Light reflects off objects
all around you. The Law of Reflection states that the angle of
incidence is equal to the angle of reflection. This law is
explained on the next slide.
Slide 44
Reflection, Refraction, and Interference You see your image in
a mirror because of regular reflection. Regular reflection happens
when light reflects off a very smooth surface. All the light beams
bouncing off a smooth surface are reflected at the same angle.
Slide 45
Reflection, Refraction, and Interference You cannot see your
image in a wall because of diffuse reflection. Diffuse reflection
happens when light reflects off a rough surface, such as a wall.
Light beams that hit a rough surface reflect at many different
angles.
Slide 46
Law of Reflection: Figure 1
Slide 47
Reflection, Refraction, and Interference The tail of a firefly,
flames, light bulbs, and the sun are light sources. You can see a
light source in the dark because its light passes directly into
your eyes. Most things around you are not light sources. But you
can see them because light from light sources reflects off the
objects and the travels to your eyes.
Slide 48
Reflection, Refraction, and Interference The transfer of energy
carried by light waves is called absorption. When a beam of light
shines through the air, particles in the air absorb some of the
lights energy. As a result, the beam of light becomes dim.
Slide 49
Reflection, Refraction, and Interference An interaction of
light with matter that causes light to change direction is
scattering. Light scatters in all directions after colliding with
particles of matter. Light can be scattered out of a beam by air
particles. This scattered light allows you to see things outside of
the beam. But, the beam becomes dimmer because light is scattered
out of it.
Slide 50
Reflection, Refraction, and Interference Refraction is the
bending of a wave as it passes at an angle from one material to
another. Refraction of light waves occurs because the speed of
light varies depending on the material through which the waves are
traveling. When a wave enters a new material at an angle, the part
of the wave that enters first begins traveling at a different speed
from that of the rest of the wave.
Slide 51
Reflection, Refraction, and Interference A lens is a
transparent object that refracts light to form an image. Convex
lenses are thicker in the middle than at the edges. When light
beams pass through a convex lens, the beams are refracted toward
each other. Concave lenses are thinner in the middle than at the
edges. When light beams pass through a concave lens, the beams are
refracted away from each other.
Slide 52
Reflection, Refraction, and Interference Your brain always
interprets light as traveling in straight lines. But when you look
at an object that is underwater, the light reflecting off the
object does not travel in a straight line. Instead, it
refracts.
Slide 53
Refraction Diagram: Figure 3 Because of refraction, the cat and
the fish see optical illusions.
Slide 54
Reflection, Refraction, and Interference White light is
composed of all the wavelengths of visible light. The different
wavelengths of visible light are seen by humans as different
colors. When white light is refracted, the amount that the light
bends depends on its wavelength.
Slide 55
Reflection, Refraction, and Interference: Figure 4 Waves with
short wavelengths bend more than waves with long wavelengths. White
light can be separated into different colors during refraction, as
shown below.
Slide 56
Reflection, Refraction, and Interference Diffraction is the
bending of waves around barriers or through openings. The amount a
wave diffracts depends on its wavelength and the size of the
barrier or opening. The greatest amount of diffraction occurs when
the barrier or opening is the same size or smaller than the
wavelength.
Slide 57
Reflection, Refraction, and Interference The wavelength of
visible light is very small. So, a visible light wave cannot
diffract very much unless it passes through a narrow opening,
around sharp edges, or around a small barrier.
Slide 58
Reflection, Refraction, and Interference Interference is a wave
interaction that happens when two or more waves overlap.
Constructive Interference happens when waves combine to form a wave
that has a greater amplitude than the original waves had.
Destructive Interference happens when waves combine to form a wave
that has a smaller amplitude than the original waves had.
Slide 59
Reflection, Refraction, and Interference: Figure 5 The image
below shows what happens when light combines by interference.
Slide 60
Chapter 22 Section 3 Recap 1) What does the law of reflection
state? 2) What is the difference between regular and diffuse
reflection? 3) From Figure 1, what is the difference between angle
of incidence and angle of reflection? 4) What happens when a beam
of light shines through the air? 5) T/F Light can be scattered out
of a beam by air particles.
Slide 61
Chapter 22 Section 3 Recap 6) What is a lens? 7) How does your
brain always interpret light? 8) What is white light composed of?
9) What does the amount a wave diffracts depend on? 10) What size
is the wavelength of visible light?
Slide 62
Section 4: Objectives Name and describe three ways light
interacts with matter. Explain how the color of an object is
determined. Explain why mixing colors of light is called color
addition. Describe why mixing colors of pigment is called color
subtraction.
Slide 63
Light and Matter When light strikes any form of matter, it can
be reflected, absorbed, or transmitted. Reflection happens when
light bounces off an object. Absorption is the transfer of light
energy to matter. Transmission is the passing of light through
matter.
Slide 64
Light and Matter: Figure 1 The image below explains
transmission, reflection, and absorption.
Slide 65
Light and Matter Transparent matter is matter though which
light is easily transmitted. Glass is transparent. Translucent
matter transmits light but also scatters it. Frosted windows are
translucent. Opaque matter does not transmit any light. Computers
and books are opaque.
Slide 66
Light and Matter: Figure 2 The images below explain the
difference between the terms transparent, translucent, and
opaque.
Slide 67
Light and Matter Humans see different wavelengths of light as
different colors. The color that an object appears to be is
determined by the wavelengths of light that reach your eyes. Light
reaches your eyes after being reflected off an object or after
being transmitted through an object.
Slide 68
Light and Matter When white light strikes a colored opaque
object, some colors of light are absorbed, and some are reflected.
Only the light that is reflected reaches your eyes and is detected.
So, the colors of light that are reflected by an opaque object
determine the color you see.
Slide 69
Light and Matter Ordinary window glass is colorless in white
light because it transmits all the colors of light that strike it.
But some transparent objects are colored. When you look through
colored transparent or translucent objects, you see the color of
light that was transmitted through the material.
Slide 70
Light and Matter Red, blue, and green are the primary colors of
light. These three colors can be combined in different ratios to
produce white light and many colors of light. Color Addition is
combining colors of light. Light and Color Television The colors on
a color TV are produced by color addition of the primary colors of
light.
Slide 71
Light and Matter A material that gives a substance its color by
absorbing some colors of light and reflecting others is a pigment.
Color Subtraction When you mix pigments together, more colors of
light are absorbed or taken away. So, mixing pigments is called
color subtraction. Yellow, cyan, and magenta are the primary
pigments.
Slide 72
Light and Matter: Figure 3
Slide 73
Chapter 22 Section 4 Recap 1) What is the difference between
reflection and absorption? 2) Give 1 example of an object that is
transparent. 3) Give 1 example of an object that is translucent. 4)
Give 1 example of an object that is opaque. 5) What happens when
white light strikes a colored opaque object?
Slide 74
Chapter 22 Section 4 Recap 6) Why is ordinary window glass
colorless in white light? 7) List the 3 primary colors of light. 8)
List the 3 primary pigments. 9) From Figure 3, what color is
produced when green and blue mix together? 10) From Figure 3, what
color is produced when magenta and yellow mix together?