Blacklight Acvies Saturday Science Club

Blacklight Acvies

Author: Robby Ferguson

Acvity Descripon

The following acvity is meant to provide a basic overview of the electromagnec spectrum in addion to elaborang on some of the more interesng characteriscs of light.

Goals/Objecves

• To learn the different parts of the electromagnec spectrum • To be able to disnguish between colors that are contained within the visible light spectrum and those that are outside of that range • To understand what phosphors are and how they are affected by ultraviolet light • To learn the definion of luminescence and the difference between chemiluminescence and bioluminescence

Needed Supplies

• a relavely powerful blacklight • tonic water • tap water • highlighters • permanent markers • paper

Experiment Steps

1. Start by discussing a very basic overview of the electromagnec spectrum. To make the spec- trum more clear to the students, draw a simplified version of the spectrum on the whiteboard (referring to the first link in the References secon).

2. Explain to the students that there are all kinds of electromagnec waves around us all the me, but the only ones that we can see are in the visible light spectrum, which includes violet, blue, green, yellow, orange, and red.

3. Turn on the blacklight, and turn off the overhead lights in the room. Ask the students what color they see.

4. Although they should see violet or purple, explain that the blacklight is also projecng ultra- violet light, and show them where ultraviolet light falls on the electromagnec spectrum.

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5. Temporarily turn the overhead lights back on.

6. Describe how we cannot actually see ultraviolet light because it is a shorter wavelength than the visible spectrum.

7. Put a bole or glass of tonic water and a bole or glass of regular water together on a table.

8. Ask the students if they noce anything different about the tonic water and the regular water. Some may menon that they see bubbles in the tonic water, but be sure to emphasize that there is no color visible in either liquid.

9. Turn the overhead lights back off, and shine the blacklight on each liquid. The tonic water should glow under the blacklight, while the regular water remains uncolored.

10. Explain to the students that things that glow under a blacklight, like the tonic water, contain phosphors, which are a special substance that emits visible light when excited by radiaon, such as the ultraviolet light. The tonic water contains phosphors, but regular tap water does not.

11. This glowing effect is a form of luminescence. Ask the students if they can think of anything else that glows. Although there may be many answers, describe how glow scks and light- ning bugs are two examples of different types of luminescence. Glow scks light up due to a chemical reacon that takes place when you bend them, and this glowing is called chemilumi- nescence. Lightning bugs also light up due to a chemical reacon, but because the reacon happens inside their bodies, the glowing is referred to as bioluminescence.

12. For a final experiment, give each child a piece of copy paper and ask them to write two mes- sages on them, one in permanent marker and one in highlighter. Tally the number of students who think the permanent marker has more phosphors and the number of students who think the highlighter has more phosphors.

13. Shine the blacklight on each student’s paper. The students should easily see that the high- lighter glows under the blacklight and, therefore, contains more phosphors than the perma- nent marker.

References and More Informaon

1. http://www.clivemaxfield.com/diycalculator/imgs/console-07.gif

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