Transcript 10.1 The speed of light

Electricity, Sound and Light
10.1 Properties of light
• Every time you see
something, light is
involved.
• Light rays in the room
reflect off the page and
into your eyes.
• The reflected light
carries information that
allows your brain to
form an image of the
page.
10.1 Properties of light
• Light travels fast and over
long distances.
• Light can carry energy and
information.
• Light travels in straight lines.
• Light can be bent by lenses
or reflected by mirrors heat
and warmth.
• Light has color.
• Light can be bright or dim.
10.1 Light comes from atoms
• In order to get light out
of an atom, you must put
some energy into the
atom first.
• Making light with heat is
called incandescence.
• Atoms in the filament
convert electrical energy
to heat and then to light.
10.1 Light comes from atoms
• 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.
10.1 Color and energy
• We call the combination of all colors white light.
• Not all light has the same energy.
• Color is how we perceive the energy of light.
10.1 Color and energy
• Just as matter is
made of atoms, light
energy comes in tiny
wave bundles called
photons.
• Each photon has its
own color (energy).
10.1 Color and energy
• All of the colors in the
rainbow are light of
different energies.
• Red light has the
lowest energy we can
see, and violet light
the highest energy.
• As we move through
the rainbow from red
to yellow to blue to
violet, the energy of
the light increases.
10.1 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”.
10.1 Wavelength
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).
Wavelength and Frequency of Visible Light
10.1 What kind of wave is light?
• Light is an electromagnetic
wave.
• Red light is a traveling
oscillation (wave) with a
frequency of about 450 THz.
• If you could shake the
magnet up and down 450
trillion times per second, you
would make waves of red
light.
Electromagnetic Waves
• Waves that can travel through vacuums, where
there is no matter, are electromagnetic waves.
• The sun emits electromagnetic waves that travel
through space and reach Earth.
– The energy carried by electromagnetic waves is
called radiant energy.
10.1 The electromagnetic
spectrum
• The entire range of electromagnetic waves,
including all possible frequencies, is called the
electromagnetic spectrum.
• This spectrum includes visible light and invisible:
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radio wave
microwaves
infrared light
ultraviolet light
X-rays
gamma rays
10.2 The human eye
• The eye is the sensory
organ used for vision.
• The retina contains lightsensitive cells called
photoreceptors.
• Photoreceptors convert
light into nerve impulses
that travel through the
optic nerve to the visual
cortex of the brain.
10.2 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.
10.2 How we see color
• Our eyes work
according to an
additive color
process — three
photoreceptors (red,
green, and blue) in the
eye operate together
so that we see millions
of different colors.
10.2 Making an RGB color image
• Color images in TVs and
computers are based on
the RGB color model.
• A television makes
different colors by
lighting red, green, and
blue pixels in different
proportions.
10.2 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.
10.2 How objects appear to be
different colors
• 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.
10.2 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.
10.2 Why plants are green
• Plants absorb
energy from light
and convert it to
chemical energy in
process called
photosynthesis.
• Chlorophyll is the main pigment used in
photosynthesis.
10.2 Why plants are green
• Chlorophyll
absorbs mostly
blue and red light,
and reflects green
light.
• Plants must reflect
some light to avoid
absorbing too
much energy.
10.3 Basic optical devices
Three useful optical devices are:
1. lenses
2. mirrors
3. prisms
10.3 Basic optical devices
• A magnifying glass is
a converging lens.
• In survival situations,
it can be used to
make a hot spot.
• Mirrors can attract
the attention of
rescue teams from
great distances.
10.3 Four ways light is affected
by matter
10.3 Four ways light is affected
by matter
• All four interactions almost
always happen together.
• A glass window is mostly
transparent but also
absorbs about 10% of light.
• The glass scatters some
Can you tell which
light (translucency) and
colors are reflected and
reflects some light.
which are absorbed?
10.3 Light rays
• Reflection occurs when light bounces off a surface.
• Refraction occurs when light bends while crossing
through materials.
10.3 Reflection
• There are two types of reflection; not all form
images.
• A ray of light that strikes a shiny surface (like a
mirror) creates a single reflected ray.
• This type of reflection is called specular
reflection.
10.3 Reflection
• A surface that is dull, (or uneven) creates
diffuse reflection.
• When you look at a diffuse reflecting
surface you see the surface itself.
10.3 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.
10.3 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!
10.3 Lenses
• An ordinary lens is a
polished, transparent disc,
usually made of glass.
• For a converging lens, the
first surface bends light
rays toward the normal
line.
• At the second surface, the
rays bend away from the
normal line and because of
the curvature it bends
toward the focal point.
10.3 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.