Visualizations of particle-field interactions

Abstract

Visualizations within physics education are critical for learning physics and can be realized in a classroom with experiments, demonstrations, digital tools, mathematical analysis, or other representations, all with different levels of abstraction. This project aimed to determine whether the concept of field (i.e. electrical, acoustic, or optical fields) can be demonstrated, visualized, and applied in various experiments. In the first Paper, an experimental setup for visualizing charge particles’ motion in an electrical field was built. Designed learning activities were performed, and the effects on Swedish upper secondary school students’ conceptual understanding were tested. This work shows that students’ understanding of the interaction of charged particles with electrical fields increases more than without if a lecture includes an experiment that visualizes the phenomenon, either live or videotaped. In Paper II a remotely operable optical trap was realized and used to levitate and investigate charged droplets remotely from a classroom. Visualizing and measuring many fundamental physical processes are described. The motion of charged particles in electric fields and the photon pressure of light is described as well as how it can be safely demonstrated for a class. In Paper III, an optical trap is used to visualize the electron´s quantization. In this work, it was shown that the effect of a single electron addition can be magnified and observed by the naked eye and measured with a ruler analogous to Millikan’s experiment. The droplet is optically trapped and uncharged in an alternate electric field by an alpha radiation source. A strong electrical field was applied and as the uncharged droplet gained charges from the ionized air it jumped a well-defined step depending on how many electrons were added. The smallest jump corresponds to the addition of one electron, i.e. one elementary charge, and longer jumps are multiples of this. Finally, in Paper IV, a new type of experimental method to determine the volume of microliter-sized droplets in acoustic fields is described. By using a simulation of the acoustic field to assist in setting the cavity length a fast and self-calibrated method is presented.