Chapter 22—The Nature of Light
Material on the Final Exam
Section 1—What is Light?
• Objectives
– How is light an electromagnetic
wave?
– Explain how you could calculate
distances traveled by light using the
speed of light
– Explain why light from the sun is
important
Light: An Electromagnetic Wave
• Light travels as a wave
• Light does not need matter to
travel
• Light is an electromagnetic wave
– Electromagnetic waves are waves
that consist of electric and magnetic
fields that vibrate at right angles to
each other
Electromagnetic Wave
Electric and Magnetic Fields
• An electric field surrounds every
charged object
• A magnetic field surrounds every
magnet
How EM Waves are Produced
• Produced by the vibration of an
electrically charged particle
• Creates electric field
• Field starts vibrating
• Creates magnetic field
• Carries energy
The speed of light
• Fastest thing known to science
• In a vacuum
– 300,000,000 m/s
– 300,000 km/s
• Slows down in matter
• Faster than sound
The speed of light
• We can use the speed of light to
find how far it travels
• Formula
• SI units for speed: m/s
• SI units for distance: m
• SI units for time: s
Math Practice
• Math Practice
– The distance from Earth
to the moon is 384,000
km. Calculate the time it
takes for light to travel
that distance.
• You try!
– The distance from the
sun to Venus is
108,000,000 km.
Calculate the time it
takes for light to travel
that distance.
Math Practice
• Math Practice
– It takes 2595 seconds
(43 min) for light from
the sun to reach
Jupiter. How far away
is Jupiter?
• You try!
– The alpha centauri
system has two stars.
If it takes 11470s for
light to reach one star
to the other, how far
apart are they?
Light from the Sun
• Light is a major energy source for
our planet
– Plants use it to make food
– Animals eat these plants
– Fossil fuels store solar energy from
the past
Section 1—What is Light?
• Objectives
– How is light an electromagnetic
wave?
– Explain how you could calculate
distances traveled by light using the
speed of light
– Explain why light from the sun is
important
22-1 Study Guide
– Must have 3 colors
– Must draw and label and EM wave
– Must describe the two waves that make
up an EM wave
– Must show the speed of light number
– Must show the speed of light formula OR
formula triangle
– Must give 2 reasons why light from the
sun is important
Section 2—The electromagnetic Spectrum
• Objectives
– Identify the two ways that EM 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 harmful
and helpful
Characteristics of EM waves
• Light is only a teeny part of all EM
waves
• The electromagnetic spectrum is
the entire range of EM waves
– Divided by wavelength and frequency
Radio Waves
• Longest wavelengths (30+ cm)
• Lowest frequencies
• Used for broadcasting radio
signals
– Modify frequency or amplitude
(height) of wave
• AM and FM radio
Radio Waves
• FM versus AM Radio
– AM has longer wavelengths
– AM bounce off atmosphere
– FM less affected by electrical “noise”
• Why FM sounds better
Radio waves and Television
• TV signals carried by
radio waves
• Shorter wavelengths
than radio
• Higher frequencies
than radio
• Change frequency
and amplitude
• Sent to satellites to
amplify signal
Microwaves
• Shorter wavelengths (1mm-30cm)
and higher frequencies than radio
• Microwave ovens, Radar and
communication
Radar
• From microwaves
• Radio detection and ranging
• Finds speed and location of object
– Sends waves that bounce off items
Infrared Waves
• Shorter wavelengths (700 nm to
1mm) and higher frequencies than
microwaves
• “Warm” feeling on sunny day
• Heat
• Invisible for us, but can be
detected--thermogram
Visible Spectrum
• Narrow range of wavelengths and
frequencies that humans can see
• White light is the combination of
Ultraviolet Light
• Shorter wavelengths (60-400nm)
and higher frequencies than
visible light
• Both good and bad for your body
Ultraviolet Light
• Good Effects
– Kill bacteria on
food
– Sterilize surgical
tools
– Helps body make
vitamin D
• Helps with calcium
absorption
• Bad Effects
– Sunburn
– Skin cancer,
wrinkles, eye
damage
– Protected by
ozone, clothing
and sunscreen
X rays and Gamma Rays
• X rays
– .001nm-60nm
wavelength
– Medical field
– Kill cells
– Lead aprons
– Airport security
• Gamma rays
– Shortest
wavelengths
(<0.1nm) and
highest frequency
– Penetrate almost
all materials
– Treat cancer
– Kill cells
– Kill bacteria on
food
Section 2—The electromagnetic Spectrum
• Objectives
– How do EM 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 harmful
and helpful
22-2 Study Guide
– Must have 3 colors
– Must write the EM waves in order from
long λ to short λ
– Must show wavelength, frequency, and
energy trend from left to right
– Must list the two ways that EM waves
differ from each other
– Must include one use of each wave
– Give one harm for UV
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
– Explain how refraction can separate
white light into colors
– Compare constructive and
destructive interference of light
Reflection
• Reflection is when light waves
bounce off an object
– EX: mirror
• The Law of Reflection states that
the angle of incidence is equal to
the angle of reflection
– The angle it comes in is the same
angle it goes out
Types of Reflection
• Regular Reflection
is when all light
beams are reflected
at the same angle
– Smooth surfaces
• Diffuse Reflection is
when light beams
reflect at many
different angles
– Not smooth
Light Source or Reflection?
• Luminous objects produce visible
light
– Light source
• Illuminated objects are visible
objects that are not a light source
– Due to the light around it (reflection
Absorption and Scattering
• Absorption is the transfer of
energy carried by light waves to
particles of matter
– Air absorbs some energy
– Why a flashlight dims
• Farther the light source, the more light
that gets absorbed
Absorption and Scattering
• Scattering is an interaction of
light with matter that causes light
to change direction
– All directions
– See objects outside beam
– WHY THE SKY IS BLUE!
Refraction
• Refraction is
the bending of
a wave as it
passes at an
angle from one
substance to
another
Refraction
• Why does refraction happen
– Light travels at different speeds
when it goes through different things
Refraction
• When light switches materials, it
speeds up or slows down
– This changes the angle
Diffraction
• Diffraction is the bending of
waves around barriers or through
openings
– Depends on wave size
– Depends on barrier size
Diffraction and Wavelength
• Small wavelength for light!
– Does not bend much unless opening
is even smaller
– Why light does not bend around
corners
Interference
• Interference is a wave interaction
that happens when two or waves
overlap
– Can brighten: constructive
– Can dim: destructive
Constructive v. destructive interference
Section 3—Interactions of Light
Waves
• Objectives
– Describe how reflection allows you
to see things
– What is the difference between
absorption and scattering
– How can refraction separate white
light into colors
– What is the difference between
constructive and destructive
interference?
22-3 Study Guide
– Must have 3 colors
– Be able to Label and draw examples for
•
•
•
•
•
•
Regular Reflection
Diffuse Reflection
Absorption
Scattering
Refraction
Diffraction
Section 4—Light and Color
• Objectives
– Name and describe the three ways
light interacts with matter
– Explain how the color of an object is
determined
– Describe color addition and color
subtraction
Light and Matter
• When light strikes objects, it can
be
– Reflected
– Absorbed
– Transmitted
Reflection, Absorption,Transmission
• Reflection is when
light bounces off an
object
• Absorption is when
light energy is
transferred to matter
• Transmission is the
passing of light
through matter
Types of Matter
• Transparent matter is matter
through which visible light is
easily transmitted
– Ex: glass, plastic wrap
Types of Matter
• Translucent matter transmits light
but also scatters it
– Ex: frosted glass, wax paper
Types of Matter
• Opaque matter is matter that does
not transmit any light
– Ex: Aluminum foil, a book, wood
Colors of Objects
• Color is about
the reflection
of light off
materials that
hits your eyes
Colors of objects
• Opaque objects
– The colors you see are the
colors that are reflected
• White = ALL colors
reflected
• Black = ALL colors
absorbed
• Translucent
objects
– The colors you see
are the colors that
are transmitted
Mixing colors of light
• Only need 3
colors to make
white light
– Red
– Green
– Blue
• Called primary
colors of light
Color addition
• Combining colors
of light is called
color addition
• Mixing two
primary light
colors makes
secondary light
colors
Colored Television
• Television has
color because
each “dot” has a
group of red,
green, and blue
dots
• Different
combinations
give us color
Mixing colors of pigment
• A pigment is a
material that
gives a substance
its color by
absorbing some
color of light and
reflecting others
• Primary pigments
– Magenta
– Yellow
– Cyan
Color subtraction
• Mixing pigments
results in more
colors being
absorbed or
taken away—
color subtraction
22-4 Study Guide
– Must have 3 colors
– Pick SEVEN facts from this section to
include
• You can do vocab, pictures, examples, etc.
Section 4—Light and Color
• Objectives
– Name and describe the three ways
light interacts with matter
– Explain how the color of an object is
determined
– Describe color addition and color
subtraction