Sihui Wang

Hearing light from an incandescent bulb

In this paper, we present an interesting experiment to turn the vibratory light from an incandescent light bulb into audible sound. Inspired by research on the photoacoustic effect (PAE) using lasers, we construct a similar device in an undergraduate physics laboratory with everyday articles including light bulbs, glass beakers and soot. Using our device, a distinct sound is detected and analysed experimentally. Particular attention is paid to the attenuation effect of the acoustic signal, which can be explained by modifying the existing theory and using the adiabatic boundary condition according to the incident light source we use. This demonstration is a comprehensive experiment with the combination of sound, light and heat. The modification on the model can help undergraduate students gain an intuitive understanding of different boundary conditions.

Formation of birefringence patterns under everyday conditions

The interference of two polarized lights is always discussed in general optics courses, and birefringence is considered to be a way to cause polarized light. In this article, we investigate the formation of birefringence patterns under everyday conditions. We firstly present a simple method to demonstrate coloured patterns in a plastic plate with everyday utensils. Then we investigate the possibility of observing colours in plastics without Polaroids under natural incident light. We prove by theoretical calculation that polarization of the incident light is unnecessary to produce birefringence patterns except for in the normal incidence condition.

Confining rigid balls by mimicking quadrupole ion trapping

The rotating saddle not only is an interesting system that is able to trap a ball near its saddle point, but can also intuitively illustrate the operating principles of quadrupole ion traps in modern physics. Unlike the conventional models based on the mass-point approximation, we study the stability of a ball in a rotating-saddle trap using rigid-body dynamics. The stabilization condition of the system is theoretically derived and subsequently verified by experiments. The results are compared with the previous mass-point model, giving large discrepancy as the curvature of the ball is comparable to that of the saddle. We also point out that the spin angular velocity of the ball is analogous to the cyclotron frequency of ions in an external magnetic field utilized in many prevailing ion-trapping schemes.