We have observed that in implementing "Solids & Light" and/or "Luminescence: It's Cool Light!" in a high school physics classroom some instructors have focused on the concrete observational aspects of the materials and not on developing the energy model of the atom as a result of their lack of familiarity with this model. The Potential Energy Diagrams instructional unit was developed to provide both the students and instructor with experiences in reviewing energy conservation by using potential energy diagrams. We have found that when students are provided with opportunities to practice applying energy diagrams for various classical situations, they are likely to experience less difficulty when using these diagrams to explain the physical properties of light-emitting devices.

Since computer accessibility in many high school classrooms is a problem, an inexpensive alternative or supplement to the Gas Lamp Emission Spectroscopy program that has proven effective involves the use of "energy ladders" — wooden dowels or pencils placed on a piece of cardboard that contains an energy scale similar to the one found in the program. The wooden dowels represent energy levels that may be placed horizontally on the scale. Electron transitions are represented as large bold arrows drawn to scale on separate pieces of paper. Students then can place these "transitions" pointing downward between two "energy levels" to represent electron transitions that result in the emission of energy. The energy difference between the two "energy levels" is equal to energy of a resulting spectral line. On the back of these "transitions," a single vertical line of a specific color is used to identify the resulting spectral line. The energy ladder used in conjunction with the computer program provides students with a concrete, hands-on, and visual means to construct their energy level model. The use of the energy ladder could also be used to provide students with concrete experiences in constructing "electron transitions" that result in the absorption or emission of energy.

Investigations on the physical properties of luminescent devices themselves, without the introduction of energy level models of the atom, have also been adapted to provide students with a unique means to reinforce their understanding of the concepts of energy and light and to develop proficiency in scientific inquiry.¹³ For example, students can use light sticks to model how temperature affects the light emitted by a bioluminescent organism — the firefly. This investigation has been very effective and relevant in illustrating the general idea of a scientific model for audiences of all ages and cultures.

We have demonstrated that it is possible to introduce 20th-century physics ideas in an introductory university or high school physics and physical science course with the use of visual and interactive simulations, combined with interesting and relevant hands-on activities using accessible materials. The Visual Quantum Mechanics — Original materials are published by Ztek Inc., http://www.ztek.com. A sampler is available at http://web.phys.ksu.edu/vqm/index.html.