Using Gigantic Growing Spheres to Illustrate an Aspect of Rainbow Formation

Gordon R. Goreby: Gordon R. Gore
BIG Little Science Centre

Educational Innovations has a new product called Gigantic Growing Spheres (Catalogue #GB-760) which physics teachers might find useful for illustrating internal reflection. These are a very large version (about 6 cm) of the Growing Spheres (also called Jelly Balls) discussed in earlier issues of BIGScience*.

Basic Equipment Needed

1 green* laser pointer (* works much better than red)

1 fully grown ‘Giant Growing Sphere’ (about 6 cm diameter)

Materials

The growing spheres, made of polyacrylamide polymer, are delivered in a plastic envelope, about 60 to a bag. They start at about 1 cm diameter, and after soaking in water for a day or two, reach a diameter of about 6 cm.

Gigantic Growing Sphere

One use for these giant clear spheres, which are mostly water, is to illustrate internal reflection in a ‘drop’ of water, as in a cloud. A green laser pointer works very well, because of its brightness. The photo (above) shows what happens. Of course, a rainbow is the result of refraction, internal reflection and dispersion of all the wavelengths of sunlight by countless water droplets, but this is a useful simulation of what happens to one wavelength (colour) of light. Gigantic Growing SpheresIt is possible to obtain a crude spectrum (rainbow) with the growing sphere if ‘white light’ from a ray box with one slit is aimed at the sphere. (Experiment to find the best incident angle.)

Gigantic Growing Spheres

*Previous articles describing ways to use Growing Spheres (Jelly Balls) are in Volumes 142, 143 and 144 of BIGScience.

The BIG Little Science Centre was started in February 2000 by Gordon R. Gore, a retired science teacher who has dedicated his life to teaching science in an interactive environment. The Centre currently operates out of four classrooms leased from School District 73 at Bert Edwards Science and Technology School, 711 Windsor Avenue Kamloops BC, Canada.

 

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