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Waves and Light
Table of Contents
9.3
Refraction and Lenses
Ms. De Los Rios
7th Grade
Interactive Art
http://www.pearsonsuccessnet.com/snpapp/learn/navigateIDP.do?method=vlo&int
ernalId=140711110000082#
Vocabulary 9.3
1. Index of Refraction- A measure of the amount of ray of light
bends when it passes one medium to another.
2. Mirage- An image of a distant object caused by refraction of light
as it travels through air of varying temperatures.
3. Lens- A flexible structure that focuses light that has entered the
eye. A curved piece of glass or other transparent material that is
used to refract light.
4. Concave Lens- A lens that is thinner in the center than at the
edges.
5. Convex Lens- A lens that is thicker in the center than at the
edges.
What Happens When Light Hits an Object? Pg. 328
When light hits an object=
it can be reflected, refracted, and/or absorbed.
• The more transparent/see-through an object is, the less light
it will absorb.
• An opaque/solid not clear object will both reflect and absorb
light.
Reflected
Refraction
Refraction (bent) can cause you to see something that may not actually be there.
When light rays enter a medium at an angle, the change in speed causes the rays to
bend. Some mediums cause light to bend more than others.
The index of refraction of a medium is a measure of how much a light ray bends
when it enters that medium.
Pencil Animation
The refraction occurs only at the boundary. Once the light has crossed the boundary between the two
media, it continues to travel in a straight line. Only now, the direction of that line is different than it
was in the former medium.
Refraction and Lenses pg. 329
Optical Illusion In a Fish Tank
There is only one fish in the tank, but refraction makes it look as though there are two.
Refraction and Lenses pg. 330
Refraction is the bending of a
wave when it enters a medium
where it's speed (frequency speed)
is different.
Refraction of Light
The light ray bends as it passes
through different mediums.
Refraction in Different Mediums pg. 330
Some mediums causes light to bend
more than others.
• Fig. 2 light ray travels faster _____
P1
• When light passes from air into water the light
slows down.
• Then the light slows down again and bends
more when it passes from the water into the
glass.
• When light passes back from glass to air, the
light speeds up.
Refraction and Lenses pg. 330
Bending Light
The table shows the
index of refraction of
some common mediums.
What Happens When Light Hits an Object?
Prisms and rainbows pg. 331
When white light enters a prism, each
wavelength is refracted (bend) by a
different amount.
The longer the wavelength= wave is less bent by a prism
.
Prisms and Rainbows pg. 331
Which color has the longest wavelength? = _____is refracted the least
Which color has the shortest wavelength?= _____is refracted the most
• This difference in refraction causes white light to spread out into the
colors of the spectrum.
• When white light from sun shines through water droplets, the droplets act
like prisms, refracting and reflecting the light and separating the colors to
appear as a rainbow
Brainpop Rainbow
Refraction and Lenses
Rainbow
A rainbow forms when light is reflected and refracted by water droplets suspended in the
air.
Did You Know?
•
You can see the effects of
refraction even more in a diamond.
•
Light rays slow down and bend
considerably when they enter a
diamond.
• These light rays eventually exit the
diamond as bright bursts of light.
• The bursts of light give diamonds
their characteristic sparkle.
Quick Quiz
Check your understanding of these principles by determining
which color(s) of light are reflected by the paper and what color
the paper will appear to an observer.
Color virtual lab
What Happens When Light Hits an Object? Mirages Pg. 332
A mirage is an image of a distant object caused by the
refraction of light.
When light moves from hot air near the ground to cooler air
above, it refracts. You may see a mirage on a road.
What Determines the Type of Image Formed by a Lens? pg. 333
Binoculars
Eyeglasses
Cameras
A lens is a curved piece of glass or other transparent material that
refracts/bend light.
• A lens forms an image by refracting light waves that pass through it.
• Lenses can have different shapes.
The type of image formed by a lens depends on:
the shape of the lens and the position of the object.
What Determines the Type of Image Formed by a lens? Pg. 333
Characteristics of a concave lens
and images:
• Thinner in the center than at the edges.
•
A concave lens can produce only
virtual images because parallel light
rays passing through it never meet.
• The virtual images are always upright
and smaller than the object.
• The image is located where the light
rays appear to come from.
Refraction and Lenses pg. 333
Concave Lens
A concave lens produces a virtual image
that is upright and smaller than the
object.
In the second diagram, where would the
image be when the two light rays are
extended back to the same side of the
lens as the object?
What Determines the Type of Image Formed by a Lens?
A convex lens is thicker in the center
than at the edges. It acts like a
concave mirror because it focuses
rays of light. An object’s position
relative to the focal point determines
whether a convex lens forms a real or
virtual image. When an object is
between the lens and the focal point,
a virtual image forms. The image
forms on the same side of the lens as
the object. If the image is outside of
the focal point, a real image forms on
the other side of the lens. The real
image can be smaller, larger, or the
same size as the object.
Refraction and Lenses pg. 333
How a Convex Lens
Works
The type of image formed
by a convex lens depends
on the object’s position.
Which image is virtual and
which is real?
Refraction and Lenses
Lenses and Mirrors
These photos show parallel rays of light
passing through a convex lens and a concave
lens. Complete the Lenses and Mirrors table.
What Factors Affect the Speed of a Wave? pg.336
Light waves, sounds waves, and other waves move at different
speed in different materials.
The speed of a wave through a substance is
determined by the substance’s physical properties.
Light, like all E.W, consists of:
vibrating electric fields
magnetic fields
The speed of light through a substance depends on how that
substance interacts with electric and magnetic fields.
What Factors Affect the Speed of a Wave? Pg. 337
The speed of sound waves is affected by three factors—
temperature, compressibility and density
• As temperature of a medium (way) increases = the speed of
sound also increases.
•
As for solids, a temperature increase = causes wave
speeds to decrease.
What Factors Affect the Speed of a Wave? pg.337
Two other factors that determine the speed of sound through a
substance are:
the compressibility and density of that substance.
Compressibility is a measure of how
hard a substance is to compress, or
squeeze.
Density is a measure of how much
mass a given volume of a substance has.
Refraction and Lenses
The Changing Speed of Sound
Sound travels faster through steel than air, even though steel is denser,
because steel is also less compressible.
Resources
Pearson Art in Motion (Refraction, Reflection, and Rainbows)
http://www.pearsonsuccessnet.com/snpapp/learn/navigateIDP.do?method=vlo&internalId=140711110000083#
Light Absorption, Reflection, and Transmission
http://www.physicsclassroom.com/class/light/u12l2c.cfm
http://webcache.googleusercontent.com/search?q=cache:rM-LG-4ua3gJ:hyperphysics.phyastr.gsu.edu/hbase/geoopt/refr.html+&cd=2&hl=en&ct=clnk&gl=us&client=firefox-a
Color virtual lab++++++++
http://water.me.vccs.edu/courses/env211/lesson15_print.htm