Transcript Chapter 2 Using Light

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Section 1: Waves and the
Electromagnetic Spectrum
What causes waves?
What are the basic properties of waves?
What does an electromagnetic wave consist of?
What are the waves of the electromagnetic spectrum?
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Electromagnetic Waves
Believe it or not, you are being “showered” all the time, not
by rain but by waves.
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Transverse Waves
Waves that move the medium perpendicular to the direction
in which the waves travel are called transverse waves.
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Properties of a Wave
Amplitude: The maximum distance that the
medium carrying the wave energy moves away
from the resting position.
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Properties of a Wave
Wavelength: The distance between two similar
parts of a wave.
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Properties of a Wave
Frequency: The number of times a wave
passes an area in 1 second. Measured in Hertz
(Hz).
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Properties of a Wave
Speed: How fast a wave travels. Measured in
kilometers per second (km/s).
• Mechanical Waves: The speed can change
depending on the medium and the energy. Can
be slow or fast, but they can NEVER be as fast
as electromagnetic waves.
• Electromagnetic Waves: Always travel at “the
speed of light” (300,000 km per second in a
vacuum). They will slow down a bit when going
through mediums like air or glass.
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Amplitude, Wavelength, and Frequency
The basic properties of all waves are amplitude, wavelength,
and frequency.
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Mechanical Waves
Mechanical waves are produced when a source
of energy passes through a medium.
Examples:
» Sound
» Earthquakes
» Ocean waves
» “Snapping” a rope
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What Is an Electromagnetic Wave?
• An electromagnetic wave consists of vibrating
electric and magnetic fields that move through
space at the speed of light.
• They do NOT require a medium to travel.
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What Is the Electromagnetic Spectrum?
The electromagnetic spectrum is the complete
range of electromagnetic waves placed in order
of increasing frequency.
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Radio Waves
• Longest wavelength (and
lowest frequency)
• Uses the least amount of
energy (and is therefore the
safest of all E.M. waves)
• Used to broadcast FM and
AM radio signals
• Was once used to
broadcast television signals
• CB Radio (popular with
truck drivers)
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Microwaves
• Used to heat up food in
microwave ovens
• Also used for cell phone
communication
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Infrared Rays
• Usually in the form of invisible heat (stove, fire, etc.)
• Can also be used for night vision and thermography
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Visible Light
Makes up a very small part of the very large
Electromagnetic Spectrum
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Visible Light
• The human eye can only see wavelengths
between 800 nanometers (red light) to 400
nanometers (violet light).
• 1 billion nanometers = 1 meter (about 3 feet)
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Visible Light
The main colors of visible light (in order of
largest to smallest wavelength): ROY G BIV
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Visible Light
• “White light” is
actually all the colors
of the visible spectrum
blended into one.
• Light is separated
into the colors of the
visible spectrum when
it passes through a
prism.
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Ultraviolet (U.V.) Rays
• Small amounts are
useful to humans (skin
can convert UV rays into
Vitamin D).
• Buy sunblock that has
the highest UVA and UVB
protection (the best
sunblocks contain zinc
oxide).
• Large amounts are
harmful to humans
(leading cause of skin
cancer).
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X-Rays
• Can pass through most objects except dense matter
(like bone or lead).
• Excessive exposure can lead to cancer, but getting
3 - 4 X-ray exams a year is considered safe.
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Gamma Rays
• Shortest wavelength (and highest frequency).
• Most dangerous of all electromagnetic waves.
• In small, concentrated doses, can be used to kill
cancer cells.
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End of Section:
Waves and the
Electromagnetic
Spectrum
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Section 2: Visible Light
and Color
How does visible light interact with an object?
What determines the color of an opaque
object?
How is mixing pigments different from mixing
colors of light?
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When Light Strikes an Object
When light strikes an
object, the light can be
reflected, transmitted, or
absorbed.
Key Term
Transmit : to send from
one place to another
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Visible Light
Transparent: material that allows light to transmit
through it in straight lines
»examples: clear glass, clean air
Translucent: material that scatters transmitted light as it
passes through it
»examples: fog, frosted glass
Opaque: material that reflects some colors and absorbs
other colors; does not allow any light to pass through
» examples: walls, mirrors
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The Color of Objects
The color of an opaque object is the color of the light it
reflects.
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Combining Colors : Light
.
When combined in equal
amounts, the three
primary colors of light
(green, red, and blue)
produce white light.
The primary colors can
also form other colors
(example: red and green
make yellow).
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Combining Colors : Pigments
• Pigments are found in
inks, paints, and dyes.
• They absorb some
colors while they reflect
others.
• The primary colors of
pigments (magenta,
yellow, and cyan)
combine in equal
amounts to form black.
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End of Section:
Visible Light and Color
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Section 3:
Reflection and Refraction
What does the law of reflection state?
Why do light rays bend when they enter a new
medium at an angle?
What determines the types of images formed
by convex and concave lenses?
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The Law Of Reflection
When an object or wave hits a surface through which it
cannot pass, it reflects (bounces back).
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Concave Mirrors
A mirror with a surface that curves inward like the inside of a
bowl is a concave mirror.
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Concave Lenses
A concave lens will make a larger real object look like a
smaller “virtual” image.
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Examples of Concave Mirrors & Lenses
Make-Up Mirrors
Glasses for Nearsightedness
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Convex Lenses
How can you make this
tiny ladybug appear
larger?
A convex lens will make a
small real object look like
a larger “virtual” image.
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Examples of Convex Mirrors & Lenses
Blind-spot Mirrors
Magnifying Lens
Reading Glasses
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Refraction of Light
When light rays enter a medium at an angle, the change in
speed causes the rays to bend, or change direction.
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The Index of Refraction
The index of refraction of a
medium is a measure of how
much light bends as it travels
from air into the medium. The
table shows the index of
refraction of some common
mediums.
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The Index of Refraction
Interpreting Data:
Which medium causes the
greatest change in the
direction of a light ray?
Diamond causes the greatest
change in the direction of a
light ray traveling from air.
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The Index of Refraction
Interpreting Data:
According to the table, which
tends to bend light more:
solids or liquids?
According to the graph, most
solids bend light more than
liquids do (quartz is an
exception).
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The Index of Refraction
Predicting:
Would you expect light to
bend if it entered corn oil at
an angle after traveling
through glycerol? Explain.
You would not expect light to
bend if it entered corn oil at
an angle after traveling
through glycerol, because
corn oil and glycerol have the
same value for the index of
refraction.
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End of Section:
Reflection and
Refraction
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Section 4: Seeing Light
How do you see objects?
What types of lenses are used to correct
vision problems?
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Cross-Section of the Eye
___________________ :
Hole through which light
enters the eye.
___________________ :
Transparent front surface
of the eye.
___________________ :
Short, thick nerve through
which signals travel to
the brain from the eye.
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Cross-Section of the Eye
___________________ :
Ring of muscle around
the pupil.
___________________ :
Curved part of the eye
behind the pupil that
refracts light.
___________________ :
Layer of cells lining the
inside of the eyeball.
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Pupil and Iris
The iris (the colored
part of the eye) is a
ring of muscle that
opens and closes
depending on how
much light needs to
enter the eye.
The pupil (black
hole) is simply the
opening made by
the iris.
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Retina
The retina is a layer of
cells that lines the inside
of the eyeball.
Contains two types of cells:
– Rods
• able to see with very little light
• can only see black and white
images
– Cones
• respond to colors red, green,
and blue
• needs bright light to function
properly
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Correcting Vision
Concave lenses are used to correct nearsightedness.
Convex lenses are used to correct farsightedness.
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End of Section:
Seeing Light
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Section 5:
Optical Tools
How are lenses used in cameras, telescopes,
and microscopes?
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Cameras
The lens of the camera focuses light to form a real, upsidedown image on film in the back of the camera.
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Microscopes
A microscope uses
a combination of
lenses to form
enlarged images of
a tiny object.
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Telescopes
Telescopes use lenses or mirrors to collect and
focus light from distant objects.
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End of Section:
Optical Tools