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VANDERBILT STUDENT VOLUNTEERS FOR SCIENCE
VISIBLE LIGHT AND UV LIGHT
Spring 2014
LESSON OUTLINE
I. What is Light?
Give each pair of students one of the handouts. If the class has covered the section on light in their textbook (check
with teacher), ask some of the questions given in the introduction section of the lesson.
II. The Electromagnetic Spectrum
Briefly explain electromagnetic radiation and point out the different types - X rays, UV, IR, and radio
waves. Mention that the difference in energy is because of their differences in wavelength or frequency.
They all travel at 300 million meters per second (speed of light).
III. Visible Light Can Be Separated Into Different Colors
Refraction: Pass out the jars of water and stick. The stick looks broken or bent at the place where it
enters the water. This is an example of refraction, when light bends as it passes from air to water.
IV. UV Light
A. Bluing agents - Demonstration
Shine the black light on white paper, white T-shirts, white tennis shoes
B. Hands-On Activity
Students dip a Q-tip in the bottle of bluing agent and write their first name on a paper towel. When
the black light is shown on the paper towel, their name fluoresces.
C. UV Detecting Bracelet - Hands-On Activity
Students make a bracelet that they get to keep. The beads will detect UV radiation.
Shine the black light on their bracelet, and then turn it off. The UV beads will glow after the black
light is removed. You may have to turn off the room lights for them to see the beads glow.
Materials
12 Black Lights (hand-held ones)
12 jars containing water and a stick
1 container UV beads of assorted colors
25 pieces of braid for stringing beads - each one is tied off on one end with one UV
bead
25 ¼ size white paper towels
12 Bottles of Bluing Agent (UltraClorox-2)
1 bag (12) Q-tips
1 piece of copy paper
12 handouts - Electromagnetic Spectrum
SAFETY PRECAUTION: Do not look directly at the black light; ultraviolet light can
be damaging to eyes.
I. WHAT IS LIGHT?
A. What is light?
Light is a form of energy.
Light comes from the sun and also from light bulbs and fire.
The light you can see comes from the visible spectrum.
The visible spectrum is a very small part of the electromagnetic spectrum.
B. What color is visible light? Usually white.
White is actually made up of all colors.
II. THE ELECTROMAGNETIC SPECTRUM
BACKGROUND INFORMATION – this is way too difficult for 3-4th graders to understand,
and is for your information only.
Electromagnetic radiation is difficult to explain. Avoid detailed explanations of “electromagnetic” if
possible.
Much of the energy we receive on Earth comes from the sun. Energy travels in waves. Some waves,
like light, are visible; other waves are invisible. Examples of invisible waves are ultraviolet (UV),
infrared (IR), X rays, and radio waves. Both the visible and invisible forms are called electromagnetic
radiation. Radiation is the process of sending out energy waves. A light bulb radiates light. A radio
station radiates radio waves. The human body emits infrared radiation in the form of heat, which can
be detected by night vision goggles.
The difference in energy of the different forms of electromagnetic radiation is because of their
differences in wavelength or frequency. The speed of all electromagnetic radiation is the same - 300
million meters per second in a vacuum. Since visible light is the most familiar form, this speed is
usually referred to as the speed of light.
Give each student one of the handouts that include the electromagnetic spectrum and “rainbow”.
What is the Electromagnetic spectrum (EM Spectrum)?
 The electromagnetic spectrum is the arrangement of all the different types of electromagnetic
waves.
 Tell the students to look at the EM spectrum on the observation sheet.
 Discuss briefly (not more than 2 minutes) the different parts of the electromagnetic spectrum.
 Point out that there a several different types of waves – radio, microwave, infrared, visible,
ultraviolet, x-rays and gamma rays. These waves have different wavelengths, frequencies and
energies.
Point out the parts of the electromagnetic spectrum that they will be investigating today:
1. Visible light.
2. Ultraviolet light.
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III. REFRACTION AND DIFFRACTION OF VISIBLE LIGHT.
Tell student they are going to investigate two properties of light; refraction and diffraction.
Background Information for VSVS members only. Visible light is made up of all the colors that
the eye can detect. The range of colors, when mixed, looks white to the eye. The three primary
colors of light (additive primary colors) are red, green, and blue. When white light passes from one
medium (like air) to another (like water), it is refracted. Actually, each color is refracted at a
different rate - red is bent the least, while violet is bent the most. When the colors are bent and
spread out they form the color spectrum.
A. Refraction.
1. Give each group a jar containing water and a straw lying at an angle in the jar.
2. Tell the students to rotate the jar while looking at the straw. Ask them what they observe. The
straw will appear to be bent at the point where it emerges from the water.
3. Tell the students to unscrew the lid and to hold the straw vertically in the center of the jar, so that
half is in/out of the water. Look at the straw “straight on” at the center point, and then slowly move
it to the side of the glass (do not move your head with the straw). Ask them what they observe.
4. This is an example of refraction, when light bends as it passes from air to water.
Reference: http://www.physicsclassroom.com/mmedia/optics/bp.html
• Ask students to look at the visible light spectrum (the “rainbow”) and identify colors that make
up visible light. You can remember the order of the colors by naming the spectrum Roy G
B(i)v for red, orange, yellow, green, blue and violet. Indigo is no longer named in the rainbow
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spectrum.
R
O
Y
G
B
V
• Ask students where they have seen light broken into its different colors - answers may include a rainbow,
a garden sprinkler, light shining through a prism, or on an oil film.
Tell students that visible white light is separated into the colors of a rainbow by refraction. Rainbows
are a result of refraction of light through water.
IV. ULTRAVIOLET LIGHT.
Remind students that the visible “rainbow” is just a small part of the electromagnetic spectrum. There
are many wavelengths you cannot see.
Point to the UV (Ultraviolet) part of the electromagnetic spectrum on their handout.
What is UV light?
 UV stands for Ultraviolet, a portion of the light spectrum that is beyond the violet light that we can
see with our eyes.
 We cannot see UV light.
 Show the students a “black light” and turn it on.
 Where does UV light come from?
 Ultraviolet light is produced by the sun. What happens when it reaches the earth’s atmosphere?
Most UV radiation is absorbed by the atmosphere or reflected back into space.
 UV waves have higher energy than visible light.
Since we cannot see ultraviolet light, how can it be detected?
 Some chemicals absorb UV light and then re-emit the energy as visible light.
A. Activity Using Bluing Agent
Tell students that white paper, white tennis shoes, white T-shirts, and even other types of shirts may
fluoresce under UV light.
• Hold the black light over a piece of white copy paper to show that it fluoresces with a black
light.
• Hold the black light over someone's tennis shoes or over a T-shirt or article of clothing,
being careful not to shine it in anyone's eyes.
EXPLANATION: The fluorescent blue that is observed is caused by a bluing agent that is added to
tennis shoes and fabric to make them look whiter. A bluing agent is also added to laundry detergent to
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make clean clothes look whiter. These additives are called optical brighteners because they absorb UV
light and emit visible light through fluorescence. When optical brighteners are incorporated into textiles,
they make the material appear brighter and whiter, thus giving the appearance of being cleaner.
• Give each student a piece of paper towel and a Q-tip. Place the 12 bottles of bluing agent
around the room so that 2 students have access to a bottle.
 Tell them to dip the Q-tip in the bluing agent and write their first name (or a picture) on the paper
towel.
• Wait until the bluing is dry and tell students to hold the black light over their paper towel. Their
name/drawing will be fluorescent blue. If this is difficult to see, put the paper towel on top of a white
piece of paper and repeat.
The bluing agent in the bottle is UltraClorox 2. This type of additive is used along with detergent when
washing clothes.
NOTE: Students see blue color immediately after the black light is shone, but the blue color is gone
as soon as the black light is removed. This is called fluorescence. In the next example colors can be
seen for several minutes after the black light is removed – this is phosphorescence.)
V.
HOW CAN UV LIGHT BE USEFUL?
Ask the students if they know any uses for UV lights.
 Ultraviolet lights are used by forensic scientists to detect bodily fluids.
 They can also be used to kill bacteria.
 Bug Zappers use UV light to attract insects.
 They are used to detect fake dollar bills ($5 and up). This strip can be seen in visible light, but
fluoresces only under UV light. Bills of different denominations have strips that
fluoresce different colors and are at different positions on the bill. The $1 bill does not have a
strip.
How is UV light dangerous?
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Ultraviolet light has more energy than visible light, and can damage living cells.
When UVB light damages DNA, our cells might not work correctly. Sometimes this makes the
cells grow uncontrollably, a condition called cancer.
UVB light also damages the tissue in our eyes and can cause cataracts.
We should block as much UV light from our bodies as is possible.
Your Notes:
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How do you know if your skin has received too much UV light?
o It turns red and becomes tender, i.e., you get a sunburn.
What are some ways to block UV light?
o There are many ways to block UV light. They include: sunscreen, long sleeves and pants,
wide brimmed hats, sunglasses, and staying in the shade. Glass in windows transmits less
than 10% of sun-burning UV light.
VI. MAKING A UV DETECTING BRACELET
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Show the students a string of UV detecting beads. Point out that all the beads are white.
Expose the necklace to the 8 inch UV light, until the beads have turned color.
Explain that this color change is due to the presence of UV light. The beads contain a chemical
that absorbs the UV light and reemits it as colored visible light.
Point out the purple beads in the necklace and tell the students that they will be using just the
purple beads for this experiment because these change to a more intense color than the others.
For VSVS information only: The color change involves a dye molecule absorbing UV energy to produce a
different geometric isomer of the molecule. When the UV energy is removed, the color slowly fades as the dye
molecule rotates back to the more stable form. The wavelength required is between 360-300 nm, so parts of
the UV Type A and Type B will change the color of the beads. UV Type C and the radiation from
incandescent light bulbs will not cause color changes.
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Give each student a cup of 5 UV beads and 1 piece of braid for stringing the beads.
After they have finished stringing the beads, they can make a bracelet by putting the untied end
through the hole in the bead on the tied-off end and tie a knot.
Shine their black light on the beads. (The beads take a few minutes to develop the full color.)
Notice that the beads continue to glow after the black light is removed.
Tell the students they get to keep the bracelet and to use their UV detecting bracelet to measure the
amount of UV radiation on sunny days. They could keep a diary of their results – trying different
times of the day and different times of the year – summer vs. winter.
Clean-Up and Return of the Kit:
One VSVS team member should collect the used Q-tips, and paper towels and place them in the
Ziploc bag marked “Used”. Return the Ziploc bag to the kit box.
Note: Be sure to collect all black lights. Count to make sure you have 12. Check that they are turned
off and place them back in the kit box before you go on with the next section.
Written by: Mel Joesten, Professor Emeritus, Department of Chemistry, Vanderbilt University
Pat Tellinghuisen, Director and Faculty Advisor, Vanderbilt Student Volunteers for Science
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