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Transcript
Chapter 22
The Nature of Light
Preview
Section 1 What Is Light?
Section 2 The Electromagnetic Spectrum
Section 3 Interactions of Light Waves
Section 4 Light and Color
Concept Mapping
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Chapter 22
Section 1 What Is Light?
Bellringer
What do you think light is? Is light made of matter?
Can light travel through space?
Explain your answers in your science journal.
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Chapter 22
Section 1 What Is Light?
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.
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Chapter 22
Section 1 What Is Light?
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.
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Chapter 22
Section 1 What Is Light?
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Chapter 22
Section 1 What Is Light?
Light: An Electromagnetic Wave, continued
• Electric and Magnetic Fields 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.
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Chapter 22
Section 1 What Is Light?
Light: An Electromagnetic Wave, continued
• How EM Waves Are Produced 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.
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Chapter 22
Section 1 What Is Light?
The Speed of Light
• 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.
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Chapter 22
Section 1 What Is Light?
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Chapter 22
Section 1 What Is Light?
Light from the Sun
• 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.
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Chapter 22
Section 1 What Is Light?
Light from the Sun, continued
• 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.
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Main
Chapter 22
Section 2 The Electromagnetic Spectrum
Bellringer
Describe the weather conditions necessary to see a
rainbow. Why do rainbows form?
Write your answers in your science journal.
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Main
Chapter 22
Section 2 The Electromagnetic Spectrum
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.
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Chapter 22
Section 2 The Electromagnetic Spectrum
Characteristics of EM Waves
• The light that you can see is called visible light.
However, there is light that you can’t 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.
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Chapter 22
Section 2 The Electromagnetic Spectrum
Characteristics of EM Waves, continued
• 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.
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Chapter 22
Section 2 The Electromagnetic Spectrum
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Chapter 22
Section 2 The Electromagnetic Spectrum
Radio 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.
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Chapter 22
Section 2 The Electromagnetic Spectrum
Radio Waves, continued
• Broadcasting Radio Signals 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.”
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Chapter 22
Section 2 The Electromagnetic Spectrum
Radio Waves, continued
• Comparing AM and FM Radio 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.
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Chapter 22
Section 2 The Electromagnetic Spectrum
Radio Waves, continued
• Radio Waves and Television 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. They the
signals travel through cables to TVs in homes.
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Chapter 22
Section 2 The Electromagnetic Spectrum
Microwaves
• Microwaves have shorter wavelengths and higher
frequencies than radio waves. Microwaves have
wavelengths between 1 mm and 30 cm.
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Chapter 22
Section 2 The Electromagnetic Spectrum
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Chapter 22
Section 2 The Electromagnetic Spectrum
Microwaves, continued
• Microwaves and Communication Microwaves
are used to send information over long distances.
• Cellular phones send and receive signals using
microwaves. Signals sent between Earth and
artificial satellites in space are also carried by
microwaves.
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Chapter 22
Section 2 The Electromagnetic Spectrum
Microwaves, continued
• Radar 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.
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Chapter 22
Section 2 The Electromagnetic Spectrum
Infrared 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
object’s temperature. Warmer objects give off more
infrared waves than cooler objects.
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Chapter 22
Section 2 The Electromagnetic Spectrum
Visible Light
• Visible Light from the Sun 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.
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Chapter 22
Section 2 The Electromagnetic Spectrum
Visible Light, continued
• Colors of Light Humans see different wavelengths
of visible light as different colors. The longest wavelengths are seen as red light. The shortest wavelengths are seen as violet light.
• The range of colors is called the visible spectrum.
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Chapter 22
Section 2 The Electromagnetic Spectrum
Ultraviolet Light
• 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.
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Chapter 22
Section 2 The Electromagnetic Spectrum
Ultraviolet Light, continued
• Bad Effects Too much UV light can cause sunburn.
UV light can also cause skin cancer and wrinkles, and
damage the eyes.
• Good Effects 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.
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Chapter 22
Section 2 The Electromagnetic Spectrum
X Rays and Gamma Rays
• 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.
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Chapter 22
Section 2 The Electromagnetic Spectrum
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Chapter 22
Section 2 The Electromagnetic Spectrum
X Rays and Gamma Rays, continued
• 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.
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Chapter 22
Section 3 Interactions of Light Waves
Bellringer
Mirrors are common objects that most people use
every day. From your experience, how do mirrors
work and what do mirrors do to light waves?
Explain your answers in your science journal.
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Chapter 22
Section 3 Interactions of Light Waves
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.
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Chapter 22
Section 3 Interactions of Light Waves
Objectives, continued
• Explain the relationship between diffraction and
wavelength.
• Compare constructive and destructive interference
of light.
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Chapter 22
Section 3 Interactions of Light Waves
Reflection
• 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.
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Chapter 22
Section 3 Interactions of Light Waves
Law of Reflection
Click below to watch the Visual Concept.
Visual Concept
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Chapter 22
Section 3 Interactions of Light Waves
Reflection, continued
• Types of Reflection 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.
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Chapter 22
Section 3 Interactions of Light Waves
Reflection, continued
• 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.
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Chapter 22
Section 3 Interactions of Light Waves
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Chapter 22
Section 3 Interactions of Light Waves
Reflection, continued
• Light Source or Reflection? 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.
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Chapter 22
Section 3 Interactions of Light Waves
Absorption and Scattering
• Absorption of Light 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 light’s energy. As a result,
the beam of light becomes dim.
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Chapter 22
Section 3 Interactions of Light Waves
Absorption and Scattering, continued
• Scattering of Light 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.
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Chapter 22
Section 3 Interactions of Light Waves
Refraction
• 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.
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Chapter 22
Section 3 Interactions of Light Waves
Refraction, continued
• Refraction and Lenses 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.
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Chapter 22
Section 3 Interactions of Light Waves
Refraction, continued
• Refraction and Optical Illusions Your brain
always interprets light as traveling in straight lines.
• But when you look an an object that is underwater,
the light reflecting off the object does not travel in a
straight line. Instead, it refracts.
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Chapter 22
Section 3 Interactions of Light Waves
Refraction, continued
• Because of refraction, the cat and the fish see
optical illusions.
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Chapter 22
Section 3 Interactions of Light Waves
Refraction, continued
• Refraction and Color Separation 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.
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Chapter 22
Section 3 Interactions of Light Waves
Refraction, continued
• Waves with short wavelengths bend more than
waves with long wavelengths.
• White light can be separated into different colors
during refraction, as shown below.
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Chapter 22
Section 3 Interactions of Light Waves
Diffraction
• 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.
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Chapter 22
Section 3 Interactions of Light Waves
Diffraction, continued
• Diffraction and Wavelength 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.
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Chapter 22
Section 3 Interactions of Light Waves
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.
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Chapter 22
Section 3 Interactions of Light Waves
Interference, continued
• The image below shows what happens when light
combines by interference.
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Chapter 22
Section 4 Light and Color
Bellringer
What is your favorite color? In a short paragraph,
explain why you like your favorite color. Also,
explain how certain colors affect your mood.
Write your paragraph in your science journal.
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Chapter 22
Section 4 Light and Color
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.
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Chapter 22
Section 4 Light and Color
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.
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Chapter 22
Section 4 Light and Color
Light and Matter, continued
• The image at right
explains transmission,
reflection, and
absorption.
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Chapter 22
Section 4 Light and Color
Light and Matter, continued
• 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.
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Chapter 22
Section 4 Light and Color
Light and Matter, continued
• The images below explain the difference between
the terms transparent, translucent, and opaque.
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Chapter 22
Section 4 Light and Color
Colors of Objects
• 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.
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Chapter 22
Section 4 Light and Color
Colors of Objects, continued
• Colors of Opaque Objects 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.
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Chapter 22
Section 4 Light and Color
Colors of Objects, continued
• Colors of Transparent and Translucent Objects
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.
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Chapter 22
Section 4 Light and Color
Mixing Colors of Light
• 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.
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Chapter 22
Section 4 Light and Color
Mixing Colors of Pigment
• Pigments and Color 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.
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Chapter 22
Section 4 Light and Color
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Chapter 22
The Nature of Light
Concept Mapping
Use the terms below to complete the Concept
Mapping on the next slide.
magnetic fields
electromagnetic wave
reflection
electric fields
light
absorption
transmission
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Chapter 22
The Nature of Light
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Chapter 22
The Nature of Light
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