Content Benchmark P.8.C.1
Students know visible light is a narrow band within the electromagnetic spectrum. I/S
Light is everywhere in our world. We need light to see everything in our world. Seeing colors
and shapes is automatic to us, yet light is a complex topic when we study it more closely.
Scientists call the light we see visible light. They also call light, electromagnetic radiation.
Visible light is only a small portion of the electromagnetic spectrum. Light from all portions of
the electromagnetic spectrum are used by us every day. For example, dentists and doctors use Xrays to help treat their patients, lasers are used to perform surgeries, radio waves are used in
cellular communication devices, and infrared rays are used in remote controls.
Light comes from many sources, the main one being our sun, and it provides us with the energy
needed for life. Light is one way that radiant energy may be transferred from one place to
another. Scientists now recognize that light sometimes behaves like waves and, at other times,
like particles.
To learn more about light as waves and particles, go to
http://www.glenbrook.k12.il.us/gbssci/phys/Class/light/u12l1a.html
Electromagnetic Spectrum
The electromagnetic spectrum is more familiar than you might think. The microwave you use to
heat your food, the T.V. that you watch, and the cell phones you use are all using parts of the
electromagnetic radiation spectrum (EMR spectrum).
Figure 1. The electromagnetic spectrum showing the lengths of the different types of light.
(From http://science.hq.nasa.gov/kids/imagers/ems/index.html)
Visible light is only a small portion of the EMR spectrum. Visible light waves are the only
electromagnetic waves we can see, and are also the portion of the spectrum that allows us to see
things in our world. This visible part of the electromagnetic spectrum consists of the colors that
we see in a rainbow - from reds and oranges, through blues and purples.
To learn more about the electromagnetic spectrum go to
http://imagine.gsfc.nasa.gov/docs/science/know_l1/emspectrum.html
Light and Its Properties
Color
Each color has a different wavelength. Red has the longest wavelength and violet has the
shortest. When all the waves are seen together, they make white light. Red, green and blue are
known as the primary colors of light, because when they are added together, white light is
formed.
Figure 2. White light refracted through a prism to show the different wavelengths of visible light.
(From http://science.hq.nasa.gov/kids/imagers/ems/index.html)
Brightness
Brightness is defined as the amount of light over a given coverage area. For example, thinking
about the lights in your house or classroom, some lights can brighten an entire room, while
others only cover a small area around them. Brightness decreases quickly as the distance from
the light source increases. Watts is the measure of the amount of light, so brightness is measured
as Watts per square meter.
To learn more about brightness as the amount of light over a given area, go to
http://ifa.hawaii.edu/~barnes/ASTR110L_S03/inversesquare.html
The brightness of light is also related to the amount of light an object emits or reflects. This
depends on the light wave amplitude (the height of light waves). Brightness is also somewhat
influenced by wave length. For example, yellow light tends to look brighter than reds or blues.
To learn more about brightness in relation to color, go to
http://www.nature.com/neuro/journal/v2/n11/full/nn1199_1010.html
Wavelength
When thought of as a wave, light is composed of vibrating electric and magnetic fields, where
the vibrations are perpendicular (at right angles) to the direction of light energy transfer. With
vibrations perpendicular to the energy motion, all light waves are transverse (see Figure 3
below).
Figure 3. Diagram showing how wavelength is measured from crest to crest or trough to trough.
(From http://cse.ssl.berkeley.edu/light/rightside_wavelength.html)
In a transverse wave, the size of a wave is measured as its wavelength, which is the distance
between any two corresponding points on successive waves, usually peak-to-peak or trough-totrough. The unit given to the wavelength depends on what type of wave is being measured and
what area of science it is being used in. Wavelength measurements include microns, photons,
angstroms, and nanometers. For visible light, angstroms or nanometers are used. One angstrom
is equal to 10-10 meter. The SI unit for visible light is the nanometer, which is equal to 10-9
meter. Visible light band is between 400 to 800 nanometers.
For more information on the measurement units for wavelength, go to
http://eosweb.larc.nasa.gov/EDDOCS/Wavelengths_for_Colors.html
Frequency
The frequency is the number of wave peaks (or troughs) that pass a point in space during any
time interval, usually one second. It is measured in units of cycles per second, or Hertz (Hz).
Figure 4. The electromagnetic spectrum showing the relationship between the different types of
light, their wavelengths, frequencies, and photon energy.
(From http://son.nasa.gov/tass/images/cont_emspec2.jpg)
All electromagnetic radiation travels at the speed of light which is 300,000 kilometers per second
or 186,000 miles per second, in a vacuum. Because light travels at a constant speed in a vacuum,
frequency is directly related to wavelength. As wavelength increases, frequency decreases. For
example, in the visible spectrum, red has the longest wavelength, which means is has the lowest
frequency. On the other hand, blue light has the shortest wavelength and the greatest frequency.
For more information on the relationship between wavelength and frequency, go to
http://www.physclips.unsw.edu.au/jw/EMspectrum.html
Reflection
Figure 5. Diagram of light reflecting off a smooth surface.
(From http://science.howstuffworks.com/light10.htm)
On a flat, smooth surface, light hitting the surface at some angle is reflected off the surface at an
equal angle. Mirrors, which are flat, smooth surfaces, work the way they do, based on this
principle. For rough surfaces, the light is reflected in many different directions.
Reflection also is what allows us to see things that don’t provide their own source of light. For
example, when we see an object painted blue, all of the wavelengths are being absorbed by the
object except blue, which is being reflected into our eyes. Our eyes then interpret the color and
object using the brain.
Figure 6. Diagram of how light being reflected off a blue object.
(From http://acept.asu.edu/PiN/rdg/color/color.shtml)
Refraction
The bending of light as it passes from one medium or material to another is called refraction.
Depending on the new medium, the light will travel faster or slower. When white light shines
through a prism, the white light is refracted, or bent into the colors of the visible light spectrum.
Water vapor in the atmosphere can also break apart wavelengths creating a rainbow.
For more information about light refraction and rainbows, go to
http://www.eo.ucar.edu/rainbows/.
Refraction is also used to explain why objects appear bent when they are partially in water. For
example, if you place a pencil in a beaker that is filled with water, the pencil will seem bent
because the speed of light is changing from the air to the water and the light angle is bent.
Figure 7. Angles of light traveling through air and water.
(From http://sol.sci.uop.edu/~jfalward/physics17/chapter12/chapter12.html)
Diffraction
Diffraction is the slight bending of light as it passes around the edge of an object. The amount of
bending depends on the relative size of the wavelength of light compared to the size of the
opening. If the opening is much larger than the light's wavelength, the bending will be almost
unnoticeable. However, if the two are closer in size or equal, the amount of bending is easily
seen.
Figure 8. Light being diffracted through cloud droplets.
(From http://ww2010.atmos.uiuc.edu/(Gh)/guides/mtr/opt/mch/diff.rxml)
To learn more about light diffraction, go to
http://library.thinkquest.org/C006027/html-ver/op-diffract.html
Temperature and Radiation
All objects above the temperature of absolute zero radiate energy in the form of electromagnetic
waves. As the temperature of an object increases, the frequency of electromagnetic radiation
emitted by that object also increases. For example, the average temperature of the universe is
about 2.7 K, and therefore, ubiquitous microwave light is emitted throughout the universe (called
the cosmic microwave background). Most of the planets in our Solar System have surface
temperatures that are around 100 K up to about 1000 K, and therefore, predominantly emit
infrared. Our Sun and most stars predominantly emit visible light because their photospheres are
around a few thousand degrees to tens of thousands of degrees. Even hotter objects, such as
white dwarf stars and black holes predominantly emit ultraviolet and X-rays.
Figure 9. The relationship between temperature of an object, the predominant kind
of light it emits, and the wavelength of light.
(From http://chandra.harvard.edu/resources/illustrations/xlightScale.html)
Although the temperature determines the predominant frequency of light emitted by an object, it
turns out the objects truly emit all parts of the electromagnetic spectrum, even if the amount of
some types of light is very, very small. The profile of the quantity of different types of light
emitted and the object’s temperature is called the black body curve. A black body is a
hypothetical condition showing ideal conditions for radiation emitted at a particular temperature.
Figure 9. Blackbody radiation curves for objects at three temperatures.
(From http://www.astro.washington.edu/larson/Astro101/LecturesFraknoi/graphics/blackbody.jpg)
For more information on the relationship between temperature, electromagnetic radiation, and
black bodies, go to
http://feps.as.arizona.edu/outreach/bbwein.html
Content Benchmark P.8.C.1
Students know visible light is a narrow band within the electromagnetic spectrum. I/S
Common misconceptions associated with this benchmark
1. Students inaccurately assume that we see because light shines on things and brightens
them.
What we see when we are looking at an object is the light reflecting off it. The eye converts that
light into nerve impulses and our brain tells us what we are seeing by interpreting those signals.
Students tend to think that light is shining into our eyes and that is what allows us to see objects.
They struggle to understand that we are seeing light being reflected off an object to our eyes.
They assume that we cannot see in the dark because there is no light hitting our eyes rather than
knowing that there is not light hitting the objects in the dark.
For more information on how we see, go to
http://www.accessexcellence.org/AE/AEC/CC/vision_background.html
2. Students have difficulty understanding how we see colors.
When an object appears green, it is actually absorbing all colors of light, except green. That is
the color being reflected to our eyes which is why we see it as green. Students tend to think that
white light is illuminating the object so that our eyes can see the color the object is. They need
to understand that white light is made of all the visible colors and that objects absorbing and
reflecting certain wavelengths allows us to see color. Using prisms to refract color and
discussing how a black shirt feels warmer helps students move past this misconception.
For more information on how we see colors, go to http://www.artsparx.com/seeingcolor.html
3. Students incorrectly believe that visible light is the only type of light.
Light has been used to describe light bulbs, flash lights, day light, and neon light. However, light
is not what we say when we refer to radio waves, ultraviolet, or X-rays. Students are lead toward
this misconception because visible light is such a frequent item in their lives and it is the only
radiation referred to as “light” during daily conversation. By discussing microwaves and
infrared as light and talking about sunburns being caused by ultraviolet light, students begin to
understand that visible light is only a small part of the electromagnetic radiation spectrum.
To learn more about this and other misconceptions about light, go to: http://amazingspace.stsci.edu/eds/overviews/myths/light.php.p=Teaching+tools@,eds,tools,%3EMyths+vs.+re
alities@,eds,tools,type,myths.php
Content Benchmark P.8.C.1
Students know visible light is a narrow band within the electromagnetic spectrum. I/S
Sample Test Questions
Questions and Answers to follow on a separate document
Content Benchmark P.8.C.1
Students know visible light is a narrow band within the electromagnetic spectrum. I/S
Answers to Sample Test Questions
Questions and Answers to follow on a separate document
Content Benchmark P.8.C.1
Students know visible light is a narrow band within the electromagnetic spectrum. I/S
Intervention Strategies and Resources
The following is a list of intervention strategies and resources that will facilitate student
understanding of this benchmark.
1. Interactive Simulations
Interactive on-line simulations allow students the opportunity to see how light behaves without
using expensive equipment. For example, the University of Colorado has created a site which
allows students to experiment with mixing different colors of light, as well as different pigments.
Students can then contrast how these light and pigments are different.
To see the way light colors and pigments interact, go to
http://www.colorado.edu/physics/2000/tv/colortv.html
Another website allows students to place mirrors at different angles and locations to see how
light reflects. Then it has a multiple choice quiz for students to take.
To try this activity, go to
http://www.bbc.co.uk/schools/ks2bitesize/science/activities/see_things.shtml
2. Online Quizzes
Interactive quizzes allow students to practice what they know and realize what they need to
study. These sites have multiple choice quizzes that students can take and then see their results
along with the correct answers. It also includes tutorials and online labs to use.
For an online quiz about the electromagnetic spectrum, go to http://glencoe.mcgrawhill.com/sites/0078617766/student_view0/chapter3/chapter_review_quizzes-eng_.html
To study light and its properties, go to http://glencoe.mcgrawhill.com/sites/0078617766/student_view0/chapter4/chapter_review_quizzes-eng_.html
3. Puzzles and Flash Cards
On-line crossword puzzles and flash cards are great ways for students to practice vocabulary and
concepts. Both of these sites allow students to match vocabulary to the definitions and check to
make sure they are correct. They also have tutorials the students can go back to if they need to
study more.
A crossword puzzle on light is found at http://glencoe.mcgrawhill.com/sites/0078617766/student_view0/chapter4/interactive_tutor.html#
A concentration game on waves is found at http://glencoe.mcgrawhill.com/sites/0078617766/student_view0/chapter3/interactive_tutor.html#
4. Lesson Plans about the Electromagnetic Spectrum.
NASA’s Chandra X-ray Observatory has an education website with lessons that are classroom
ready. The site includes introductory material, reinforcement activities and labs, and
performance assessment activities.
To see and download these lessons, go to http://chandra.harvard.edu/edu/formal/ems/
The Discover Education site includes a lesson plan that incorporates the electromagnetic
radiation spectrum with an extension activity that debates whether or not the government should
be able to control radio and television frequencies.
To access this lesson and others, go to
http://school.discoveryeducation.com/lessonplans/activities/electromagneticspectrum/