We present a study of the maximum stress supported by elastics bands of nitrile as a function of the natural length and the load time. The maximum tension of rupture and the corresponding variation in length were found by measuring the elongation of an elastic band when a mass is suspended from its free end until it reaches the breaking point. The…

In 1923, Weyl published a (not widely known) protocol for the calculation of redshifts. It is completely independent of the origin of the shift and treats it as a pure Doppler shift. The method is comprehensive and depends solely on the relation between the world lines of source and observer. It has the merit of simplicity of statement and…

Educational versions of Millikan's oil-drop experiment have frequently been criticized; suggestions for improvement either focus on technical innovations of the setup or on replacing the experiment by other approaches of familiarization, such as computer simulations. In our approach, we have analysed experimental procedures. In doing so, we were…

We introduce a modification to the matching Ronchi test to visualize lens aberrations with simple and inexpensive equipment available in educational optics labs. This method can help instructors and students to observe and estimate lens aberrations in real time. It is also a semi-quantitative tool for primary tests in research labs. In this work…

Bose-Einstein condensation (BEC) is discussed at the level of an advanced course of statistical thermodynamics, clarifying some formal and physical aspects that are usually not covered by the standard pedagogical literature. The non-conventional approach adopted starts by showing that the continuum limit, in certain cases, cancels out the crucial…

This work demonstrates an experiment on the optoelectronic properties of a p-n junction suitable for students of undergraduate physics. It investigates, from an educational point of view, the origin of the wavelength of radiation emitted by a light emitting diode (LED) and determines the emission wavelength of an infrared LED without using…

Hologram recording and holographic interferometry are intrinsically sensitive to phase changes, and therefore both are easily perturbed by minuscule optical path perturbations. It is therefore very convenient to bank on holographic setups with a reduced number of optical components. Here we present a compact off-axis holographic setup that…

As is well known, the positron was discovered in August 1932 by Carl Anderson while studying cloud chamber tracks left by cosmic rays. Far less known is the fact that a few months before Anderson's discovery, in April 1932, Frederic Joliot and Irene Curie had missed an opportunity to discover the positron during a nuclear physics experiment. One…

This paper is an elementary introduction to particle diffusion in a medium where the coefficient of diffusion varies with position. The introduction is aimed at third-year university courses. We start from a simple model of particles hopping on a discrete lattice, in one or more dimensions, and then take the continuous-space limit so as to obtain…

We propose a simple and fascinating experiment for studying diffusion in gels using a pH-sensitive dye. By doping agar with methyl red, we obtain a gel which rapidly reacts to changes in pH by changing its absorption spectrum. The pH gradients can be followed using a digital camera, and we demonstrate here that the pH-sensitive colour changes can…

It is shown that the well-known linear variation of p-n diode terminal voltage with temperature at different fixed forward currents allows easy and accurate determination of the semiconductor ideality factor and bandgap from only two data points. This is possible if the temperature difference required to maintain the same diode voltage drop can be…

A chain assumes the well-known shape known as a catenary when it hangs loosely from two points in a gravitational field. The correct solution of the catenary was one of the early triumphs of the newly invented calculus of variations at the end of the 17th century. Here we revisit the catenary and show that, for a chain hanging from a horizontal…

This paper describes an interesting sound phenomenon from a modern copy of the Chinese ancient variable bell which can emit distinctly different sounds at different temperatures. By means of audition--spectrum analyser software--and PC, the sound signals of the variable bell are collected and the fundamental spectra are shown on the PC. The…

We report a simple experiment that clearly demonstrates a common error in the explanation of the classic experiment where a small piece of paper is put over a book and the system is let fall. This classic demonstration is used in introductory physics courses to show that after eliminating the friction force with the air, the piece of paper falls…

Is it possible to compare approximately inertial frames in the inertial property? If this is the case, the inertial property becomes a measurable quantity. We give a positive answer to this question, and discuss the general principle of design of devices for making the required measurements. This paper is intended for advanced undergraduate and…