Explorers Club

The Rushmore Explorers Club began a new year of science and nature investigation with a meeting in September, 2009 that focused on ultraviolet radiation, or UV.

After greeting the returning club members and welcoming the new ones, Mr. Ramsey demonstrated with a prism how what we consider “white light” is really a combination of all the colors in the rainbow. The students then discussed how this range of visible light really represents only a tiny portion of what is known as the electromagnetic spectrum. The electromagnetic spectrum is made up of all types of radiation, most of which we have no way to perceive with our usual senses. Radiation of lower energies than visible light falls below the red end of the visible spectrum, and include such categories as radio waves, microwaves, and infrared.

At the other end of the spectrum (literally!) is radiation that is higher in energy than visible light. These include things such as x-rays, gamma rays, and cosmic rays, all of which pack enough of a punch to penetrate human tissues and cause (in sufficient doses) cell damage and resulting problems such as cancer or even death. Many things in our universe produce these potentially lethal energies, but luckily for us here on Earth our atmosphere blocks the vast majority of them.

Higher in energy than visible light but not as powerful as those other dangerous types is ultraviolet radiation. Ultraviolet radiation lies just beyond the purple end of our visible spectrum, and while not strong enough to pass through a human body, it is strong enough to penetrate our skin and do damage to the layers underneath. The most obvious sign of this is a sunburn, and prolonged exposure to too much UV can itself cause skin cancer.

Mr. Ramsey then pulled out the “stars” of this session, several packs of plain, innocent-looking white beads. The key came when the group tromped out of the classroom and out into the schoolyard—once the cover was removed and the beads were exposed to sunlight, within a few seconds they began turning from white to bright colors of red, orange, yellow, green, blue, and purple. Mr. Ramsey explained that these beads are made of plastic but also contain a material that is sensitive to UV radiation, and that when it hits them they turn color. Going back inside, the students observed that within just a minute or so the beads began fading back to white.

Next came the experiment part of the session. The students split into groups and separated the mass of beads into six baggies, with a variety of colors in each baggie. They then placed these baggies aside and sprayed suntan lotion onto another set of six baggies, making sure to completely coat and smear the lotion on the surface of the baggies. Two of the groups used lotion of SPF (sun protection factor—the higher the SPF number the more of the UV rays the lotion is supposed to block, thereby providing more protection than lotions with lower SPF ratings) 30, two groups used SPF 50 lotion, and two groups used SPF 85 lotion. The baggies with the beads were then placed inside these lotion-coated baggies, with the two layers of baggies representing the outer parts of our skin and the beads themselves representing the inner parts. After discussing how the lotion should keep the beads from turning color as strongly as they would without any “protection,” the students predicted that they would see the beads change color the most in the SPF 30 baggies and change the least inside the SPF 85 baggies. With that idea in mind, outside the Explorers again headed, this time with lotion-smeared baggies full of beads in hand.

So did our predictions come true? Well, sort of. It was immediately obvious that the suntan lotion blocked some of the UV radiation, as the beads in all of the baggies turned color a bit but were much more muted than when they received direct exposure. The surprising thing, though, was that there was nowhere near as much difference among the baggies as we expected. In fact, based on a quick glance, Mr. Ramsey had difficulty even identifying which baggie had which strength of lotion on it—for the most part, the beads looked very similar inside all of the baggies. In particular, there seemed to be little difference between the SPF 30 and SPF 50 baggies, indicating that perhaps the difference between the two strengths is not as great as the number ratings would suggest.

Briefly going back inside, the Explorers thoroughly washed their hands to remove all traces of the lotion and then put the beads into bowls. They discussed how several different science fair experiments could be designed around the same type of activity they had just performed, and then they all headed back outside with the bowls of beads. For the remainder of the session they strung the beads onto lengths of string to make bracelets (and in a few cases necklaces) in color patterns that they designed.

To see some photos from our ultraviolet light explorations, click on the “Gallery” link below!

Gallery

NOTE: The beads were purchased from a science toys and supplies web site—click on this link to visit the site and then search for “energy beads.”

Steve Spangler Science