Light Energy through online lessons and activities.
Teachers can expect to address the following basic concepts:
1. identify a variety of natural and artificial sources of light
2. describe the behavior of light
3. distinguish between objects that produce their own light and those that
reflect light from another source
4. identify color as a property of light
This unit has been geared toward students from grades four through eight.
Objective
Identify a variety of natural and artificial light sources
Directions:
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Brainstorm with students sources of natural light (the sun, fireflies)
Brainstorm with students sources of artificial light (a candle, a light bulb,
lamps, headlights and tail lights on vehicles, lights in stadiums)
Student Assignment:
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Students create a Light Title Page in their Science workbooks using
brainstorming ideas for illustrations
Display brainstormed information in the form of a chart with two columns,
labelling illustrations (i.e. Natural Sources || Artificial Sources)
What’s Next?
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Introduce Light Vocabulary
Introduce Light Vocabulary Definitions
Background Information for Teachers:
What is Light? http://tqd.advanced.org/13405/intro/what.html
Light Basics: http://www.opticalres.com/kidoptx.html
SEE END OF UNIT PLAN FOR DEFINITIONS
Is a candle an example of a natural or artificial source of light?
natural
artificial
Background Information
Light waves travel through the air in straight line lines.
Student Assignment: Broken Pencil Experiment
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Arrange students in small groups (4-5)
Materials: drinking lass, water, pencil
Directions
1. Fill a glass about ¾ full with water
2. Place a pencil in the glass, at a slant
3. Observe the pencil above and below the water line. Invite students to
share their observations.
Observations
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Light travels through the air in a straight line but bends when it moves
from one medium to another (e.g. water)
Looking through water changes the way light appears to travel.
The bending of light is called refraction.
When you put a pencil in a glass of water, the pencil seems to bend at the
water line.
What is the bending of light called?
refraction
reflection
Background Information
This is a sorting activity.
Definitions According To Merriam-Webster Dictionary
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Transparent: to show through
Translucent: transmitting and diffusing light so that objects beyond cannot
be seen clearly
Opaque: blocking the passage of radiant energy and especially light
Student Assignment
To determine whether an object is transparent, translucent or opaque
Materials
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A flashlight and container with about 10-15 objects - some of which are
transparent, translucent or opaque
Be sure to include objects with different attributes (thickness, shape, etc. e.g. seran wrap, fabric, foil
Directions
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Provide a flashlight and shoe box containing with the various objects. Be
sure that some are transparent, some translucent and some opaque.
Invite students to sort objects using the flashlight to examine them.
Objects can be sorted by similarities and differences. Attributes can
include colour, shape, size, texture . . .)
Would you classify tin foil as transparent, translucent or opaque?
transparent
translucent
opaque
Background Information
Sunlight or light may appear “white” but it is really made up of different colours.
Red, blue and green are Primary colors of Light. You can make any color
combination from those three colors.
A rainbow is a band of coloured light that shows the colours of the spectrum. It is
caused by sunlight hitting water particles in the air and splitting the light rays into
colors of the spectrum, as a prism does. The colors of the rainbow are red,
orange, yellow, green, blue , indigo and violet (acronym: ROYGBIV)
Student Assignment
To investigate color as a property of light
Materials
flashlight, overhead projector, prism, color paddles, paper plates, tempera paint
(primary colors)
Directions
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Shine a light (overhead projector/flashlight works well in a classroom)
through a prism to produce a spectrum.
Place colour paddles in the path of the light. Paddles should be used
individually, in pairs and in groups.
Compare those results to the way we mix paint! Fill paper plates with each
of the primary colours and allow students to mix the paint to compare and
contrast results.
Questions: What three colours can be made by combining colours of light?
Think of the various combinations that are possible!
Observations
Describe and illustrate a rainbow.
Additional Activities
Be sure to check out:
The Franklin Institute: http://sln.fi.edu/tfi/activity/physics/op-3.html
Optics for Kids: http://www.opticalres.com/kidoptx.html#WhiteVsLaser
Circles of Light: http://www.geom.umn.edu/education/calc-init/rainbow/
Background Information
The angles of incidence and reflection are the inner angles as measured from the
ray to the normal line. The normal is an imaginary line perpendicular to the
mirror.
Understanding Angles
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Incident Ray: the ray of light going toward the mirror
Reflected Ray: the ray of light bouncing off the mirror
The angles of incidence and reflection are always equal.
Visual Aids: http://www.mathresources.com/reflection.htm
Student Assignment
To measure the angles of incidence and reflection
Materials
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A mirror
Flashlight
Protractor
Try These Activities
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To understand reflection of light, be sure to check out:
http://ww2010.atmos.uiuc.edu/...
Reflection and Refraction:
http://www.cybertours.com/...
Check out how these angles appear in rainbows:
http://www.unidata.ucar.edu/...
Challenge your students to measure angles like these!
What do the angles of incidence and reflection have in common?
they are not equal
they are equal
Design an experiment that demonstrates that light travels in a straight
line. You may use these materials: a flashlight, a dark room, a fork, a
piece of black construction paper.
Be sure to follow this outline
Purpose
(Why am I doing this activity?)
To find out how light travels
Apparatus
(Materials)
Method (Steps I would take to do the experiment)
Observation
(What did I see?)
Conclusion
(What did I learn?)
Below are some of the definitions that students will need to be familiar with as
they study the theme of Light.
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Angles
the angle of incidence and the angle of reflection are always equal
Light
o Is energy that you can see
o travels in a straight line
Prism
o is a specially shaped transparent object that is used to separate
light
o as white light passes through a prism, it is separated into bands of
colour (known as the visible light spectrum): red, orange, yellow,
green, blue, indigo, violet
o Reflection
objects are seen by the reflection of light
o Rays
in demonstrating reflection, light rays are given names such as:
incident ray, reflected ray, the normal
o Incident Ray
is the ray of light going toward the mirror
o Reflected Ray
is the ray of light bouncing off the mirror
o
o
o
the Normal Ray
is a line perpendicular to the mirror at the
point the light hits
o Rainbows
are caused by water in
the air splitting the
sunlight into the colours
of the spectrum
Concave Lens
 a concave lens causes light to spread out or diverge
 a mirror in which the reflecting surface curves inward is
called concave
 a concave mirror makes things look bigger than the real
objects
 e.g. the inside of a spoon’s bowl (the shape is like the inside
of a cantaloupe carved out)
Convex
 a convex lense causes light to converge, or focus
 a mirror in which the reflecting surface curves outward is
called convex
 a convex mirror makes things look smaller
 e.g. the back of a spoon’s bowl, side-view mirrors on trucks

o
o
o
Transparent
light passes through transparent objects
Translucent
some light passes through translucent objects
Opaque
no light passes through opaque objects
What does a convex lens cause light to do?
focus
convey
converge
Light Basics
What is light?
It's a kind of energy called "electromagnetic (EM) radiation" (but
this kind of radiation is not harmful, except for an occasional sunburn). There are other
kinds of EM radiation too (radio waves, microwaves, x-rays, etc.), but light is the part
WE can see, the part that makes the rainbow.
How does light travel?
FAST and STRAIGHT.
How FAST?
About 186,000 miles per second
[300,000 kilometers per second], so light from the sun
takes about 8 minutes to go 93 million miles [149
million kilometers] to earth. Does this seem SLOW?
Well, if you could DRIVE to the sun at 60 mph [100
kph], it would take you 177 years to get there! In one
second, light can go around the earth 7 times!
How STRAIGHT? Perfectly straight, until something bends it. The straight paths of
light are called LIGHT RAYS.
Controlling Light
There are THREE basic ways to control light:
1. Block it with something (this makes a shadow)
2. Reflect it (change its path with a mirror):
This is called REFLECTION, strangely enough.
3. Bend it:
Change its direction by making it pass into another transparent material of
different density, like glass or water. This is called REFRACTION, and it's
how lenses work.
The fine print:There are actually other ways to bend or deflect
light, including diffraction gratings and holographic lenses.
These depend on the wave nature of light, and are a little more
difficult to explain. Scientists have also found that gravity can
bend light, but it takes a very large object with strong gravity
such as a star to bend light very much, so it's not an effect you
see every day!
Why do we CARE about controlling light ANYWAY?
Well, some important, useful, and very cool "things" depend on being able to
produce, control, and/or detect light in special ways:
Your eyes
Eyeglasses and contact lenses
Lenses for TV, movie, and photographic cameras
Photocopiers and fax machines
Binoculars and telescopes
Microscopes and magnifiers
Projectors (overhead, movie, slide, TV)
CD players
Supermarket product code laser scanners
Weather and spy satellites
Medical systems (to look inside the body)
Solar energy systems
...and many more (not to mention a little thing like PLANTS which use light to grow
and to make the oxygen we breathe - but engineers don't make plants).
Lenses
What are lenses? Lenses bend light in useful ways. Most devices that control light
have one or more lenses in them (some use only mirrors, which can do most of the same
things that lenses can do).
There are TWO basic simple lens types:
CONVEX or POSITIVE lenses will
CONVERGE or FOCUS light and can form
an IMAGE
CONCAVE or NEGATIVE lenses will DIVERGE (spread
out) light rays
You can have mixed lens shapes too:
Complex Lenses
Simple or Complex? Simple lenses can't form very sharp images, so lens designers
or optical engineers figure out how to combine the simple types to make complex lenses
that work better. We use special computer programs to help us do this because it can take
BILLIONS and BILLIONS of calculations.
Camera lens This complex lens has 6 simple lens elements - click the small picture
to see the whole camera.
Zoom lens for home video
camera (13 elements)
A professional TV zoom
lens used to broadcast
sports could have 40
elements and cost over
$100,000!
Magnifying Glass: A simple optical device
This diagram (click it to see a bigger version) shows how a magnifying glass
bends light rays to make things look bigger than they are. Many optical
devices use the same basic idea of bending the light to fool your eye and
brain so light LOOKS like it came from a different (usually larger or closer)
object.
White Light and Laser Light
What is "White light?"
Regular light from the sun or from a light bulb really contains all the colors of
the rainbow. But you have to split it up to see this.
Can light split???
YES! You can split up white
light into its colors with a
prism (raindrops act like tiny
prisms when they make a
rainbow in the sky, and a CD
can break the light up into
colors because it has fine
grooves like a diffraction
grating or a hologram)
So what's a laser?
A laser is a special source of
light of only one pure color (or
WAVELENGTH). You can't break
up laser light into other colors.
What's Cool About Lasers?
FOCUS!
Lasers can be focused to a very small spot and can shine for long distances
without spreading out very much (unlike a flashlight which spreads out a lot)
ENERGY!
The spot contains a lot of energy - so much that some lasers can cut through
thick metal (and smaller ones are used as scalpels in some kinds of surgery)
INFORMATION!
Lower-power laser systems can be used to send and pick up information. For
example,
the product code scanner in a supermarket uses a laser, lenses, rotating
mirrors, and a computer to "read" bar codes from products. And the tiny laser
in a CD player reads EVEN tinier bumps and holes that record the music like
Morse Code (bumps and holes are used something like dots and dashes)
COMMUNICATION!
Lasers can also send information through long threads of glass called
OPTICAL FIBERS. A single laser can send thousands of phone conversations
through a fiber at the SAME TIME.
HOLOGRAMS!
Lasers are also used to make 3-D pictures called HOLOGRAMS (some
engineers are working on moving holograms, so someday we may have
AMAZING 3-D TV pictures - click here to learn more about holograms)
Scientists and Engineers
Aren't they the same thing?
Not quite. Though they use many of the same ideas and methods, scientists
and engineers are somewhat different.
What do scientists want?
Scientists want to know how the universe works. They may see it as an
enormous jigsaw puzzle to solve for its own sake. Some things they find are
useful right away, others not (though much of what scientists have found in
the past has turned out to be useful in some way). Though they certainly
want to help people, their major goal is understanding, not usefulness.
What about engineers?
Engineers try to use the facts of science and math to do things that are useful
to people. Many engineers are designers -- designing the many products that
we use in the world, from computers to cars to camera lenses.
What do they have in common? Quite a few things, actually. Scientists and engineers
both use the facts and methods of science, and both often use MATH and COMPUTERS
in their work.
Some Questions Scientists Might Ask About Light
What is light?
How is light produced by matter?
Why are things different colors?
Why is the sky blue?
Why do some things reflect lots of light and others very little?
Why are some things transparent?
How and why does light bend?
How fast does light travel?
Is light a particle, a wave, or something else?
Why does light change some materials?
More fine print: Some of these questions are answered in A
Gentle Introduction to Optical Design on this site (this is a
slightly more technical discussion of optics). For others, try
going to a Web search site such as AltaVista and typing the
question there! Another thing to search for is "physics FAQ,"
which exists in several places on the Net and answers a lot of
interesting questions. Another great resource on the Web is
Scientific American's "Ask the Experts," where you can do just
that, and also browse through the archives of past questions.
Some Questions Engineers Might Ask About Light
Light lets us see things -- how can we control light to see better?
To
To
To
To
correct poor vision? (Glasses)
see things that are far away? (Telescopes)
see very small things? (Microscopes)
see in the dark? (Night vision goggles)
Light can change matter (e.g., sun turns skin red) -- can we use this fact?
To capture images of things to see later? (Photos, movies, TV, holograms)
To cut or shape things? (Laser surgery, laser drills, etc.)
To make electricity from light? (Solar cells and other solar energy systems)
Light moves fast and can carry information - how can we use this?
To get information from the world? (TV cameras, laser scanners, robot vision)
To communicate? (Optical fiber telephone systems)
To store a lot of information? (CDs, holograms)
Careers
The world needs scientists and engineers!
Scientists and engineers are important members of our society. We need
science and technology to live in the modern world -- to have products we
want, to communicate, to travel, to understand and protect the environment,
and much more.
What do they do?
Scientists and engineers usually do a variety of things in their jobs and are
usually well paid. It's not all math, computers, reading, and writing (though
these are important skills). Many scientists and engineers travel for parts of
their jobs (knowing a foreign language can be very useful). In the past, the
majority of scientists and engineers have been men, but more and more
women have been entering these fields in recent years, and there are good
opportunities for anyone with a curious mind!
What about Math?
Math is important, but good reading and writing skills, common sense,
curiosity, and general knowledge are also important. You need to have four or
more years of college to be an engineer or scientist (most scientists and
many engineers go to graduate school after college to increase their
knowledge and get advanced degrees).
Other Options: Optics (optical science) and optical engineering are specialized but
very useful and interesting fields, though there are many, many other areas too.
Science or engineering can be fun!
Conclusions
Optics is the science of light
Devices that control light are common and important in our daily lives
Many optical devices use lenses and lasers
Scientists and engineers use similar facts and methods (like math and
computers), but their goals are different
Science or engineering can really be fun!