Ultraviolet Light

Vanderbilt Student Volunteers for Science

Fall 2011

IA. Electromagnetic Radiation• Give each student:

– one electromagnetic spectrum handout.

– One instruction sheet.• Explain the electromagnetic

spectrum:– Light is an electromagnetic

wave.– Different types of waves according

to wavelengths, frequencies and energies – radio, microwave, infrared, visible, ultraviolet, x-rays, & gamma.

– Visible light is made of many colors.

• Explain that the focus is on ultraviolet light

IB. What is UV Light?

• UV stands for ultraviolet, a portion of the light spectrum beyond what our eyes can see.

• Explain that UV light has a shorter wavelength and thus has a higher energy than that of visible light.

• Ask students to look at the visible light spectrum and identify colors that make up visible white light.– ROY G B(I)V Acronym is

useful. (Note that the “I” has been removed.)

R O Y G B VLong Wavelength Short wavelength 700 nm 400 nm

IB. What is UV Light? (Cont.)

• Demonstrate a wavelength:– Draw a wave on the board– The infrared waves are longer

and of lower energy than visible light;

– The ultraviolet waves are shorter and of higher energy than visible light.

• UV Rays:– Produced by the sun.– Most UV radiation is absorbed

by the atmosphere or reflected off.

– There are three categories of UV light: UVA, UVB, and UVC

II. Activities and DemonstrationsA. How Can It Be Detected?

• Using a paper towel and a Q-tip,

apply bluing agent, and write

VSVS in big letters on the paper

towel.

• Hold the black light over the paper

towel, and allow the letters to

fluoresce.

• Hold black light over a piece of

copy paper, a newspaper, and

someone’s tennis shoes to see if

they fluoresce as well.

• NOTE: explain the difference between

fluorescence (light disappears as soon as

source is removed) and phosphorescence

(slow disappearance).

IIA. Narra Wood Water Extract Fluorescence Demonstration

• Shine a black light on the jar labeled “narra wood extract,” and show the fluorescence that results.

• Show the students a small piece of narra wood, and explain what narra wood is and its historical significance.– Source: narra (species name:

Pterocarpus indicus) is a tropical hardwood found in Southeast Asia, the Philippines, and Malaysia, which is used for furniture, carpentry, and carving.

– Historical Significance: The fluorescence of narra wood was the first recorded example of fluorescence over 400 years ago.

IIB. How Can UV Light Be Useful?

•Ask students if they know any uses for UV lights.

•Mention antimicrobial, insecticidal, and forensic uses of UV light.

•Tell students to look at their handout sheet to see the $20 bill showing the fluorescing strip.

IIC. How is UV Light Dangerous?

• Ultraviolet light has more energy than visible light, and can damage living cells. This can cause cancer, cataracts, sunburn…

• We should block as much UV light from our bodies as is possible.

• What are some ways to block UV light? Sunscreen, long sleeves and pants, wide brimmed hats, sunglasses, and staying in the shade.

IIC. How is UV Light Dangerous?

• Ask students how they could test if the goggles prevent UV light from damaging their eyes.

• Place a UV detecting bead inside a goggle, and hold both over the black light to demonstrate.

• Students should put their goggles on until the end of the lesson.

II.Discuss the Ozone Hole

• Ask the students if they know how the earth’s atmosphere is protected from too much UV radiation.

– In the upper atmosphere, ozone is a “good” gas, since it screens out dangerous UV rays.

• Ozone information:– it is an essentially colorless gas (pale blue at high concentrations) that has a

distinctively sharp and unpleasant smell.

– Ozone is naturally formed in the atmosphere when UV rays react with O2.

• Ozone hole information:– The amount of screening of UV radiation from ozone has decreased by about 3%

over the last decade. – An ozone hole forms over Antarctica every spring. – Ozone losses over the Antarctica may contribute to changes in ozone over the

whole globe.– Ozone depletion is primarily caused by chlorine contained in chlorofluoro

carbons (CFC’s).

III. Testing UV Blocking Materials

•Tell students they will be testing several items to see how well they block UV radiation (all students and VSVSers wear goggles). UV-sensitive beads will be used to determine the amount of radiation that gets through.

•There will be three trials: each trial will consist of one control bead at the center of the plate with two experimental objects (with beads on them) on either side (make sure to line up beads between black lines on plate).

1.Trial 1 will include SPF 45 or lower sunscreen (spread on acetate slide), sunglass lens and a piece of a t-shirt.

2. Trial 2 will include white and yellow milk carton material.

3.Trial 3 will include a pill bottle and a rectangle of glass.

Leave plates directly on top of the black light for 2 minutes, and have students record the results.

All materials Trial 1

Trial 2 Trial 3

IV. Review results

• Ask students:– Does sunscreen really work? Yes

– Do sunglasses block UV? Yes

• You may want to elaborate that these sunglasses were cheap.

– Does clothing protect you from UV light? Yes

– Which milk jug gives better protection? Yellow

• Purity advertises that their milk is better because it came in a yellow plastic carton.

– Are they right? Yes – Are drugs protected in the yellow bottles? Yes.

– Typical window glass transmits some UVA but not UVB (this is why you don’t get sunburned while driving in a car with the windows up).

Clean up

• Clean-Up and Return of the Kit:

• Collect plates and put in a separate plastic bag (this is done to

prevent sunscreen from contaminating the plates.

• Students should place everything else (especially the acetate with

bead covered with sunscreen – we wash and reuse these) back in their ziploc bag.

• VSVS members will collect and return everything to the VSVS lab.

Note: Be sure to collect all black lights. Count to make sure you have nine. Check that they are turned off and place them back in the kit box before you go on with the Review Sections.

V. UV-Detecting Bracelets• Give each student a container of 5 UV

beads and 1 piece of braid for string beads.

• Tell the students to string the beads onto

the braid. After they have finished stringing

the beads, they should make a bracelet by

putting the untied end through the hole in

the bead on the tied-off end and tying a

knot.

• When they are finished, they should shine

their black lights on the beads.

• Students can keep the bracelets and

measure the amount of UV radiation on

sunny days.