July 2025
Volume 93, Issue No. 7
Determining the charge-to-mass ratio of the electron using old TVs: A low-cost approach Available
In this work, an innovative and low-cost experimental setup was developed to measure the electron charge-to-mass ratio (q/m). It uses a cathode ray tube (CRT) obtained from an old mini-TV. This paper shares plans for constructing the required electromagnet, its power supply, and a high-voltage source for accelerating the electrons in the CRT. The experimental setup can cost as little as $40. The electron beam displacement on the CRT screen can be used to determine the q/m ratio, making this an effective approach for modern experimental physics in high school and undergraduate courses.
EDITORIAL
In this issue: July 2025 by John Essick; Jesse Kinder; Claire A. Marrache-Kikuchi; Beth Parks; B. Cameron Reed. DOI: 10.1119/5.0282016
Call for papers: Special issue on motivating physics learning through research applications by Beth Parks. DOI: 10.1119/5.0282126
PAPERS
Pre-instruction diagnostic tests can predict grade probabilities in introductory physics Available by David E. Meltzer; Dakota H. King. DOI: 10.1119/5.0255768
Editor's Note: This large-scale study (2141 students across 31 classes at 5 institutions with 8 instructors) shows that students who score in the top and bottom quartiles of pretests are much more likely to earn grades in the top and bottom quartiles, respectively, compared to the chances that they will move between these quartiles. Physics instructors will want to consider the implications of these results.
Initial evidence that peer instruction is less effective for physics students with lower quantitative preparation in a highly heterogeneous class by Eric N. Smith; Jacob Helwig; Kathryn Hendren; Jane M. Huk; Vernita Gordon. DOI: 10.1119/5.0070669
Editor's Note: Physics education researchers advocate for classroom experiences that are more interactive than traditional lectures in order to foster improved student interest, engagement, and grades. This paper compares learning outcomes in two sections of an introductory mechanics course at a large public research university, one taught via peer instruction and the other with interactive lectures. Students enrolled in the peer instruction sections earned lower grades than did those in the interactive sections as well as lower gains in understanding foundational concepts if they entered with lower incoming quantitative SAT scores. The authors recommend further consideration of whether peer instruction is the optimal pedagogy for heterogeneous populations of students.
On the analogy between spinning disks coming to rest and merging black holes by Domenico Davide Meringolo; Francesco Conidi; Alessandra Mercuri; Massimino Sposato; Riccardo Cristoforo Barberi; Giuseppe Pucci. DOI: 10.1119/5.0208307
Editor's Note: Did you know that nearly everyone carries a black hole in their pocket? Okay, not an actual black hole, but a good analog to some of its properties. This paper shows that if you take a coin and make it spin on a (relatively) flexible platform, the platform's vertical acceleration mimics the gravitational waves emitted by two black holes merging together. Moreover, the precession angular velocity of the spinning disk exhibits a scaling in time similar to that of the orbital angular velocity of the black holes. This paper is for you, if you want to spice up your undergraduate mechanics classes or labs.
Quantum solutions for the delta ring and delta shell by Luis F. Castillo-Sánchez; Julio C. Gutiérrez-Vega. DOI: 10.1119/5.0256321
Editor's Note: Analyzing the one-dimensional Dirac delta-function potential is a rite of passage in quantum mechanics. Its bound state energy and reflection and transmission coefficients are familiar to most physicists. But what about the higher-dimensional analogs of the familiar spike in one dimension: a two-dimensional Dirac ring or a three-dimensional Dirac bubble? In this paper, the authors derive the bound state spectrum as well as the transmission and reflection coefficients for these potentials to reveal similarities and surprising differences in the behavior of particles in one, two, and three dimensions. The analysis is suitable for an undergraduate or graduate quantum mechanics course, adding two more exactly solvable potentials for the quantum canon. The calculations also provide interesting application of Bessel functions and spherical harmonics that could augment courses in mathematical methods.
Minimum-error state discrimination and Fano's inequality by Georgios M. Nikolopoulos. DOI: 10.1119/5.0268023
Editor's Note: A common problem in quantum information applications is the need to determine a system's quantum state from a list of possible non-orthogonal states, a procedure that will always involve some possibility of error. Fano's inequality sets a lower bound on the error probability, but this bound is often lower than the actual probability achievable through the optimal measurement procedure. For many problems, the optimal measurement procedure is not known. This paper considers a set of problems for which the optimal procedure actually is known and compares the error probability with the bound from Fano's inequality. The paper will be useful to instructors in quantum information and quantum computing courses as well as quantum mechanics instructors who wish to include these applications in their courses.
An accessible planar charged particle trap for experiential learning in quantum technologies by Robert E. Thomas; Cole E. Wolfram; Noah B. Warren; Isaac J. Fouch; Boris B. Blinov; Maxwell F. Parsons. DOI: 10.1119/5.0243389
Editor's Note: This paper presents the design and use of a charged particle surface trap, where all the electrodes are in a plane, an architecture commonly used in ion trap research. The authors demonstrate that macroscope-sized lycopodium spores, charged by the tribo-electric effect, can be trapped, shuttled, and split by their setup, providing a model system that allows students hands-on access to the technology underlying the promising use of ion traps for quantum computing. The trap design, key physics principles, and experimental procedures and results are presented, along with a computational method of data analysis. This work is appropriate for undergraduate instructional laboratory and is accessible to those both inside and outside the fields of quantum information and AMO physics.
INSTRUCTIONAL LABORATORIES AND DEMONSTRATIONS
Determining the charge-to-mass ratio of the electron using old TVs: A low-cost approach by Wenderson R. F. Silva; Ernesto Von Rückert; Joaquim B. S. Mendes. DOI: 10.1119/5.0242164
Editor's Note: Measuring the electron charge-to-mass ratio is an important part of many undergraduate laboratory courses, but the required equipment is quite expensive. In this paper, the authors show how a TV tube can be repurposed as a cathode ray tube and share circuit diagrams for the necessary electrical components. Building the apparatus could make an excellent student project that would enable future students to perform the experiment.
Experimental physics with a homemade cycling power meter: Development and characterization by René Blommaert; Maena Franzinetti; Vincent Gosse; Quentin Thomas; Philippe Maire; Emmanuel Abraham. DOI: 10.1119/5.0270674
Editor's Note: This manuscript describes how, with affordable and widely available components, one can construct a device to measure the real-time power output of a cyclist. The authors describe the design and construction of their crank-based cycling power meter and how they met numerous technical challenges, including strain and angular velocity measurements, mobile analog-to-digital conversion, battery power management, Bluetooth communications, and cycling-computer communications protocols. This multidisciplinary project draws on knowledge from physics, electronics, and computer science and will be of interest to professors looking for an accessible Capstone-type project or an advanced electronics/programming laboratory course exercise of keen interest to many physics students, especially cyclists.
BOOK REVIEWS
Elusive: How Peter Higgs solved the mystery of mass by David Derbes. DOI: 10.1119/5.0283807
Additional Resources
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