Written By Kennda Lynch!
Sunday, April 8, 2012
Electromagnetic Spectrum - Part 1
Light & Color
Lesson Objective: The objective of this lesson is for students to learn and understand some
basic principles about electromagnetic energy, why light is only a small part of the entire EM
spectrum and how 7 why we can see colors.
Standards Addressed - Science, Matter & Energy
SC.05.41.01.03 - Energy comes in many forms such as light, heat, sound, magnetic,
chemical, and electrical.
SC.05.81.02.03 - There are different forms of energy and those forms of energy can be
changed from one to another, but total energy is conserved.
SC.05.81.04.03 - Recognize that waves such as electromagnetic, sound, seismic, and
water have common characteristics and unique properties.
SC.05.53.01.03 - Earth and Sun provide a diversity of renewable and nonrenewable
resources.
Materials: Color and Light Video from "Science in Action" series (Note: your local library
should have this or should be able to get it).
Estimated Time: 1 Hour
Background: Light is a form of energy also known as electromagnetic energy or radiation.
This energy moves through space and is generated from multiple sources. What we know as
"light rays" s only the visible region of the electromagnetic (EM) spectrum that we can detect
Figure 1. Electromagnetic Spectrum (image courtesy of NASA)
with our eyes and the rest of the EM spectrum is made up of other rays such as infrared rays,
gamma rays, radio rays and x-rays.
Different types of EM energy moves at different speeds. We measure and define the different
types of EM energy by using Frequency and Wavelength.
Wavelength - EM energy moves in waves much like the waves of the ocean. Each type of
energy has a different length of wave that we call wavelength. A wavelength is the distance
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Written By Kennda Lynch!
Sunday, April 8, 2012
Figure 2. Wave Length Definition (figure courtesy of NASA)
between two crests of a given wave as shown in figure 2. Each type of EM energy has it's own
range of wavelengths. For example, as shown in figure 1, the visible spectrum has
wavelengths between 400 and 700 nanometers whereas X-rays are found between 0.001 and
10 nanometers.
Frequency - Different wavelengths of EM energy travel at different speeds and we measure
this using a unit called frequency. Frequency is defined as the number of wave crests that
pass a given point within one second. One wave (or cycle) per second is defined by a unit
called a Hertz (Hz). So, a wave that has 4 wave crests (or cycles) pass a given point in one
second has a frequency of 4 Hz. Shorter wavelengths have higher frequencies and longer
wavelengths have shorter frequencies.
Energy - The amount of energy in each EM wave depends on the type of wave. Longer
wavelengths have lower frequencies and are moving slower, so it takes less energy to move
them. Shorter wavelengths have higher frequencies and are moving faster, hence they require
more energy.
Our primary source of electromagnetic energy is from the sun, however there are other natural
sources of light such as light from a firefly. Humans have also developed ways to make
artificial light.
Procedure:
Before showing this video, review the basics of light and energy. Discuss where light comes
from and how light supports life on earth: providing heat to warm the planet, plight for
photosynthesis in plants and Vitamin D synthesis in humans, etc.
There are three parts to the video. Watch each section then stop the video and review the
following concepts and definitions for each section. Note: the video asks several questions at
the end of each section, that can be answered after watching the next section.
Part 1 - What is Color?
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Written By Kennda Lynch!
Sunday, April 8, 2012
White light - White light is the visible region of the electromagnetic spectrum. All the colors
rays that we see in a rainbow, for example, are contained in white light.
Refraction - Refraction is when light is bends through a prism as shown in figure 3. Each color
in the visible spectrum is a ray of electromagnetic energy and therefore has it's own
Figure 3. White light being refracted through a prism to generate a rainbow spectrum.
(image courtesy of NASA).
wavelength and frequency. So, when the light passes through the prism, each color bends at
a slightly different angle and exits the prism at a slightly different speed and so the light leaves
the prism in distinct colors that correspond to each color's wavelength. The water droplets in
the sky after it rains act as tiny prisms, hence why we have rainbows.
Opaque, Transparent, Translucent - Different objects allow different amounts of light through.
•
•
•
Transparent objectives, glass for example, let most of light through completely, so that
an image of the other side of the object can be seen clearly.
Translucent objects allow some light through so that an image on the other side of the
object can be seen, but not clearly.
Opaque objects do not let any light through. Instead they either absorb or reflect light
that hits it.
Absorption & Reflection - if light cannot be transmitted through an object, such as an opaque
object, then it is either reflected or absorbed. We see color because objects have pigments,
both natural and synthetic. Different pigments absorb certain wavelengths of visible light and
reflect the others. The wavelengths that are reflected result in color. The wavelengths that are
absorbed are not seen.
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Black - The color black means the object is absorbing all the wavelengths of the visible
spectrum.
White - The color white means that the object is reflecting all the colors of the visible spectrum
Part 2 - Primary Colors & Color Mixing
Primary Colors of Pigment - Magenta, Yellow, and Cyan. All colors can be made by mixing
these three colors. Each of the primary colors reflect two primary colors of light.
• Magenta - Reflects Blue & Red
• Cyan - Reflects Blue & Green Light
• Yellow - Reflects Red and Green
Subtractive Mixing - When two primary colors are mixed, only the primary colors that are
reflected in both will be seen, the other colors get absorbed/subtracted. When all three colors
are mixed, you get black (figure 4).
Figure 4. Additive vs subtractive color mixing.
Primary Colors of Light - Red, Green and Blue. All color of light are in these three colors.
Additive Color Mixing - Mixing primary colors of light, adds to the total amount of light being
reflected in our eyes. So, when you add all three colors, you get white light.
Part 3 - Artificial Light.
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Written By Kennda Lynch!
Sunday, April 8, 2012
Incandescent light - Uses heat to generate light. Electricity flows through a filament and heats
it which generates light.
Fluorescent/Neon light - Do not use heat to produce light. They are called luminescent light.
Electricity flows through a tube/bulb that has a special coating and contains a specific gas.
The gas and the electricity react and generate white light.
LASER - Light Amplification by Stimulated Emission of Radiation. Device that produces and
intense beam of light of one color/wavelength.
References:
1. Video - Color & Light. Science in Action Series. TMW media group. http://
www.tmwmedia.com/sci_in_action.html
2. Energy Quest - http://energyquest.ca.gov/index.html
3. Science Fun - http://scifun.chem.wisc.edu/homeexpts/Chemilum.html
4. Light: A Question and Answer Book. Adele Richardson. Capstone Press, 2006. Mankato,
MN.
5. NASA: Mission: Science. Tour of the Electromagnetic Spectrum -http://
missionscience.nasa.gov/ems/index.html
6. NASA's Imagers Website: The EM Spectrum - http://science.hq.nasa.gov/kids/imagers/
ems/
7. DIY Calculator - http://www.diycalculator.com/popup-m-cvision.shtml
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