Playing with light July 20 2015, 0 Comments

Summer is a great time to play, and I still enjoy playing with my science observations. Light and color are great subjects for exploration. Put it all together and here’s what I’ve been doing.

First of all I ordered a bag of UV beads from Loose in the Lab, a company in Salt Lake City, UT. These beads are available from a number of suppliers on the Internet. They are plain white beads in artificial lighting, but when they are outdoors in sunlight, they turn bright colors. A substance that reacts to something we can’t see and allow us to see it is often called an indicator, and these beads are an indicator of light that has too short a wavelength for us to see.

I noticed one day that these UV beads developed pale colors on the window sill, where the glass should have filtered out any ultraviolet light. Either the window glass was letting in a some UV or the beads were coloring from the shortest of visible wavelengths.

I checked the ability of shorter wavelength visible light to color the beads using a window sill prism that projects a nice spectrum of light across the room. I placed the bag of UV beads in the “rainbow” and saw that the beads in the violet light at the top of the spectrum caused some of the beads to color. The beads that turned blue and purple in sunlight also colored lightly in violet light. None of the beads in red, yellow, green, or blue light changed color.

I also researched window glass transmission of UV light on the Internet. I thought that glass blocked UV, and I found that it does block UVB, the wavelengths that cause sunburn and allow us to make vitamin D in our skin. I was surprised to learn that glass transmits appreciable quantities of UVA, the longer UV wavelengths that age skin and can cause cataracts. It is unlikely that any seating in your classrooms put children in direct sunlight in the middle part of the day because of the heat, but if so, you may want to move them to avoid UVA. Morning and afternoon sun is less intense, so sunlight at that time is not such a hazard.

The beads that colored in the violet part of the spectrum tell me that the shortest wavelengths of visible light will cause color change, and I suspect that the UVA coming through the window is strong enough to change them as well because the colors were stronger on a sunny window sill than in the violet light. The sunlight coming through an acrylic skylight colors the beads quickly, but not as deeply as direct sunlight, so I suspect that the skylight cover transmits a lot of UVA. In case you are wondering, polycarbonate plastic, which is often used in safety glasses, blocks all UV light. Children should have these safety glasses if they use UV or “black” light. Their eyes are specially sensitive to UV damage.

What can children learn out of this experiment? Different wavelengths of light are different colors, and the shorter wavelengths (violet) carry more energy than the longer wavelengths (red). There are wavelengths of light that we can’t see, but other substances allow us to detect them.

Children can address many questions using these beads. They may be interested in the ability of clothing or other items to block UV light. Does UV light come through the clouds? Have fun finding out!

Tools for appreciating flowers May 26 2015, 0 Comments

I’m going to go off on a tangent before I discuss materials for botany studies with older elementary children. I’ve been researching an important tool for botany studies, a hand lens.

A hand lens (aka pocket magnifier) is very useful for botany studies. Many flowers have parts too small to see without magnification, and there are even whole flowers that are too small to see without this help. Regular magnifying glasses are usually 2-3X magnification, but what you need for botany is something in the 4X to 5X range. With that you can see the texture of stigmas and even the larger pollen grains on anthers.

In years past I have been able to purchase 5X glass hand lenses. The lens folded into a plastic case that protected it while it was being carried outdoors. When I tried to find more of these lenses, I found they were no longer available. I searched the Internet, especially Amazon, looking for a replacement and ordered several to try. Here’s what I found.

The only hand lens that had the magnification described on Amazon was the Bausch and Lomb 4X folded pocket magnifier, which cost about $14. I’m now carrying that one in my pocket as my personal lens, but that is a bit pricey for a classroom set. I found that the inexpensive lenses on Amazon were not as advertised. One that was listed as a 4X was actually a 2X. One with glass lenses came with a large scratch on the lens, and its magnification was half of the description. A “bug loupe” that was labeled 5X is actually closer to 3X, and it focuses only when held above the surface, not when resting on its clear plastic housing, which one presumes was there to contain the bug. My basic message: Let the buyer beware when it comes to inexpensive hand lenses.

To tell the magnification of a simple lens, first measure its focal length. You can do this by focusing an image of a light fixture or the scene outside a window onto plain paper. Then you measure the distance between the paper and the center of the lens. If you measured in inches, divide that measurement into 10. If you measured in centimeters, divide that measurement into 25. The result is the magnification. This means that a 5X lens should focus about 2 inches or 5 cm from the paper. A 4X lens should focus at 2.5 inches, and so on.

In the end, I decided that I will have to settle for plastic lenses, although they will scratch easier than glass. Acorn Naturalists has a small 5X lens for about $4, so you can get several for botany or other work. The lens is about an inch in diameter, which is easier for children to use than the narrower 10X lenses. Ten times is more magnification than one really needs, and the short focal length means that you cut off the light as you bend close to look.

With all these lenses, you need to hold the lens close to your eye and either bend down or bring the object up until it is in focus.

I hope this information helps you find the lenses you need for botany and other outdoor observations. If you have found a better alternative, please let me know.