Transcript FPS3Chap25Light-1 - Mater Academy Lakes High School

LIGHT
Chapter Twenty-Five: Light
25.1 Properties of Light
25.2 Color and Vision
25.3 Optics
Chapter 25.1 Learning Goals
Describe the properties of light.
Explain the relationship between
energy and the colors of light.
Describe waves included in the
electromagnetic spectrum in terms of
energy, frequency, and wavelength.
Investigation 25A
Color
Key Question:
 What happens when you mix different
colors of light?
25.1 Properties of light
Light travels fast over
long distances and carries
energy and information.
Light travels in straight
lines, but can be bent by
lenses or reflected by
mirrors heat and warmth.
Light has color and can
be bright or dim.
25.1 The electromagnetic
spectrum
Light, like sound and heat, is a form of
energy.
The visible light we see is part of the
electromagnetic spectrum.
25.1 Properties of light
You see book pages because light in the
room reflects from the page to your
eyes.
Your eyes and brain use the information
carried by the light to make a mental
picture.
25.1 Light is produced by atoms
Most light is produced by atoms.
When you put some energy into the
atom, it excites the atom’s electrons.
Light is produced when the electron
releases this energy.
25.1 Incandescent light
Making light with heat is
called incandescence.
Atoms in the filament
convert electrical energy
to heat and then to light.
Incandescent bulbs
are inefficient, but
their waste heat can
be useful.
25.1 Fluorescent light
To make light,
fluorescent bulbs use
high-voltage electricity
to energize atoms of
gas in the bulb.
These atoms release
the electrical energy
directly as light (not
heat), in a process
called fluorescence.
25.1 Color and energy
When all the colors of the rainbow are
combined, we see light without any
color.
We call the combination of all colors
white light.
25.1 Color and energy
Compare the hot, blue flame from a gas
stove to the orange flame of a match.
The light from a gas flame is blue (high
energy) and the light from a match is
red-orange (low energy).
25.1 The speed of light
The speed at which light travels through
air is about 300 million meters per second.
The speed of light is so important in
physics that it is given its own symbol, a
lower case “c”.
25.1 Speed of light
The speed at which electromagnetic waves
travel through air is about 300 million
meters per second.
The speed of light is so fast that when
lightning strikes a few miles away, we hear
the thunder after we see the lightning.
25.1 Wavelength and
Frequency of Light
Because the wavelength
of light is so small,
scientists measure it in
nanometers.
One nanometer (nm) is
one billionth of a meter
(0.000000001 m).
25.1 What kind of wave is light?
A sound wave is a oscillation of air.
A water wave is an oscillation of the
surface of water.
An oscillation of electricity or
magnetism creates electromagnetic
waves.
25.1 Electromagnetic waves
If you could shake
the magnet up and
down 450 trillion
times per second, you
would make waves of
red light with a
frequency of about
450 THz.
25.1 Electromagnetic spectrum
The entire range of electromagnetic waves,
including all possible frequencies, is called
the electromagnetic spectrum.
This spectrum includes visible light and
invisible waves:






radio wave
microwaves
infrared light
ultraviolet light
X-rays
gamma rays
Chapter Twenty-Five: Light
25.1 Properties of Light
25.2 Color and Vision
25.3 Optics
Chapter 25.2 Learning Goals
Explain how humans see.
Demonstrate knowledge of the
additive and subtractive color
processes.
Apply knowledge of the behavior
of light to explain why plants have
certain colors.
Investigation 25B
Reflection and Refraction
Key Question:
 How does light behave when its path is
changed?
25.2 The human eye
The eye is the sensory
organ used for vision.
The retina contains
light-sensitive cells
called photoreceptors.
Photoreceptors convert
light into nerve
impulses that travel
through the optic nerve
to the visual cortex of
the brain.
25.2 Photoreceptors
The human eye has
two types of
photoreceptors—
cones and rods.
Cones respond to
color and rods
respond to the
intensity of light.
Rod cells “see”
black, white, and
shades of gray.
25.2 How we see color
Our eyes work
according to an
additive color process
— 3 photoreceptors
(red, green, and blue)
in the eye operate
together so that we
see millions of
different colors.
25.2 Making an RGB color image
A television makes
different colors by
lighting red, green, and
blue pixels in different
proportions.
Color images in TVs and
computers are based on
the RGB color model.
25.2 Making an RGB color image
Like the rods and cones in your retina, a
video camcorder has tiny light sensors on
a small chip called a CCD.
There are three sensors for each pixel of
the recorded image: red, green, and blue.
25.2 How objects appear to be
different colors
Your eye creates a
sense of color by
responding to red,
green, and blue light.
You don’t see objects
in their own light, you
see them in reflected
light!
25.2 Subtractive color process
A blue shirt looks
blue because it
reflects blue light
into your eyes.
Chemicals known as
pigments in the dyes
and paints absorb
some colors and
reflect other colors.
25.2 The CMYK color process
The subtractive
color process is
often called CMYK
for the four
pigments it uses.
CMYK stands for
cyan, magenta,
yellow, and black.
25.2 Why plants are green
Plants absorb
energy from light
and convert it to
chemical energy
in process called
photosynthesis.
Chlorophyll is the main pigment of plants
absorbs red and blue light and reflects
green light.
25.2 Why plants are green
Plants must reflect
some light to
avoid absorbing
too much energy.
A plant will die if
placed under
only green light!
Chapter Twenty-Five: Light
25.1 Properties of Light
25.2 Color and Vision
25.3 Optics
Chapter 25.3 Learning Goals
Explain how basic optical devices
function.
Compare and contrast the
interactions of light and matter.
Distinguish between concave and
convex lenses.
25.3 Basic optical devices
Three useful optical devices are:
1. lenses
2. mirrors
3. prisms
25.3 Basic optical devices
A magnifying glass
is a converging lens
that can be used in
survival situations
to make a hot spot.
Mirrors can attract
the attention of
rescue teams from
great distances.
25.3 Four ways light is affected
by matter
All four interactions
almost always happen
together.
Green colored paper
absorbs some light,
reflects some light, and
is partly translucent.
Can you tell which
colors are reflected and
which are absorbed?
25.3 Four ways light is affected
by matter
A glass window is
mostly transparent,
but also absorbs,
scatters, and reflects
some light.
See if you can
identify where
certain colors are
absorbed and
reflected in this
picture.
25.3 Light rays
Reflection occurs when light bounces off a
surface and when light bends while
crossing through materials.
25.3 Reflection
There are two types of reflection; but not
all reflections form images.
Rays light that strikes a shiny surface (like
a mirror) create single reflected rays.
This type of reflection is called specular
reflection.
25.3 Reflection
A surface that is dull or uneven creates
diffuse reflection.
When you look at a diffuse reflecting
surface you see the surface itself.
25.3 Law of reflection
A ray diagram is an
accurately drawn
sketch showing how
light rays interact
with mirrors, lenses,
and other optical
devices.
25.3 Refraction
Materials with a higher index of refraction
bend light by a large angle.
The index of refraction for air is about 1.00.
Water has an index of refraction of 1.33.
25.3 Refraction
Vegetable oil and glass
have almost the same
index of refraction.
If you put a glass rod
into a glass cup
containing vegetable oil,
the rod disappears
because light is NOT
refracted!
25.3 Lenses
An ordinary lens is a
polished, transparent
disc, usually made of
glass.
The shape of a
converging lens is
described as being
“convex” because the
surfaces curve
outward.
25.3 Lenses
The distance from the center of the lens to
the focal point is the focal length.
Light can go through a lens in either
direction so there are always two focal
points, one on either side of the lens.
25.3 Lenses
For a converging lens, the first surface (air
to glass) bends light rays toward the
normal.
At the second surface (glass to air), the rays
bend away from the normal line.
Searching the Cosmos
Astrophysicist Dr. Hakeem
Oluseyi (Oh-lu-SHAY-ee) is
fascinated by stars. A
physics and space science
professor at the Florida
Institute of Technology,
he has invented several
new instruments to give
astronomers a closer look
at the cosmos.