The Nature of Light

1
The Nature of Light
Chapter 22
Preview
Section 1 What Is Light? Section 2 The
Electromagnetic Spectrum Section 3 Interactions
of Light Waves Section 4 Light and Color
Concept Mapping
2
Section 1 What Is Light?
Chapter 22
Bellringer
What do you think light is? Is light made of
matter? Can light travel through space? Explain
your answers in your science journal.
3
Section 1 What Is Light?
Chapter 22
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.

4
Section 1 What Is Light?
Chapter 22
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.

5
Section 1 What Is Light?
Chapter 22
6
Section 1 What Is Light?
Chapter 22
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.

7
Section 1 What Is Light?
Chapter 22
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.

8
Section 1 What Is Light?
Chapter 22
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.

9
Section 1 What Is Light?
Chapter 22
10
Section 1 What Is Light?
Chapter 22
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.

11
Section 1 What Is Light?
Chapter 22
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.

12
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.
13
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.

14
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 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.

15
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.

16
Chapter 22
Section 2 The Electromagnetic Spectrum
17
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.

18
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.

19
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.

20
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.

21
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.

22
Chapter 22
Section 2 The Electromagnetic Spectrum
23
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.

24
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.

25
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 objects temperature. Warmer
  objects give off more infrared waves than cooler
  objects.

26
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.

27
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 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.

28
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.

29
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.

30
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.

31
Chapter 22
Section 2 The Electromagnetic Spectrum
32
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.

33
Section 3 Interactions of Light Waves
Chapter 22
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.
34
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.

35
Chapter 22
Section 3 Interactions of Light Waves
Objectives, continued

• Explain the relationship between diffraction and
  wavelength.
• Compare constructive and destructive
  interference of light.

36
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.

37
Chapter 22
Section 3 Interactions of Light Waves
Law of Reflection
Click below to watch the Visual Concept.
Visual Concept
38
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.

39
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.

40
Section 3 Interactions of Light Waves
Chapter 22
41
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.

42
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 lights
  energy. As a result, the beam of light becomes
  dim.

43
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.

44
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.

45
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.

46
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.

47
Chapter 22
Section 3 Interactions of Light Waves
Refraction, continued

• Because of refraction, the cat and the fish see
  optical illusions.

48
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.

49
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.

50
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.

51
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.

52
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.

53
Chapter 22
Section 3 Interactions of Light Waves
Interference, continued

• The image below shows what happens when light
  combines by interference.

54
Section 4 Light and Color
Chapter 22
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.
55
Section 4 Light and Color
Chapter 22
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.

56
Section 4 Light and Color
Chapter 22
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.

57
Section 4 Light and Color
Chapter 22
Light and Matter, continued

• The image at right explains transmission,
  reflection, and absorption.

58
Section 4 Light and Color
Chapter 22
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.

59
Section 4 Light and Color
Chapter 22
Light and Matter, continued

• The images below explain the difference between
  the terms transparent, translucent, and opaque.

60
Section 4 Light and Color
Chapter 22
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.

61
Section 4 Light and Color
Chapter 22
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.

62
Section 4 Light and Color
Chapter 22
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.

63
Section 4 Light and Color
Chapter 22
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.

64
Section 4 Light and Color
Chapter 22
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.

65
Section 4 Light and Color
Chapter 22
66
The Nature of Light
Chapter 22
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

67
The Nature of Light
Chapter 22
68
The Nature of Light
Chapter 22