Low-cost and accessible laboratory experiments remain important in physics education, particularly in school and undergraduate laboratories where sophisticated commercial instrumentation is not always available. This study presents the development of a low-cost falling-ball viscometer using an Arduino platform and infrared sensors for viscosity experiments based on Stokes’ law. An automated start–stop timing mechanism was implemented to reduce human reaction errors during measurements. The system was evaluated using glycerin and cooking oil, and the measured viscosities were compared with reference measurements from a Brookfield viscometer. The developed apparatus yielded viscosity values of (0.81 ± 0.04) N·s/m2 for glycerin and (0.117 ± 0.006) N·s/m2 for cooking oil, corresponding to percentage errors of 3.5% and 9.4%, respectively. The present study focuses on the educational implementation of a sensor-based experimental system that enables students to explore viscosity measurement, experimental uncertainty, calibration procedures, and the practical application of Stokes’ law to laboratory data. Despite limitations related to temperature control, optical sensing conditions, and simplifying experimental assumptions, the developed system shows practical potential for physics laboratories and STEM (science, technology, engineering, and mathematics education.
The paper investigates the possibility of small hydrogen (SH) formation in the early Universe during an interval of about 10–80 s after the Big Bang. Assuming that SH exists as proposed by the author earlier, the current study examines the cosmological conditions under which the SH can be formed and survive. The photon, baryon, and electron–positron pair densities are estimated, together with the corresponding thermal energies and temperatures, and the formation cross section required to obtain a specified SH abundance and the maximum destruction cross section consistent with SH survival are derived. Although the microscopic formation and destruction cross sections are not presently known, phenomenological constraints the cross sections must satisfy are derived for a given SH abundance. The study suggests that, if SH exists and has negligible nuclear interactions, it would not significantly participate in the standard Big Bang nucleosynthesis reaction network. The possibility that SH can undergo early cosmological decoupling, subject to the presently unknown momentum-transfer cross sections, is also discussed. If SH is formed in sufficient abundance and decouples sufficiently early, it can provide an interesting mechanism for early structure formation and may potentially contribute to the formation of black-hole seeds. This study does not establish the existence of SH, but rather examines whether the conditions in the early Universe present immediate cosmological obstacles to SH formation and survival.
Relativistic interaction of ultra-intense laser pulses with cluster targets is of particular interest for high-energy-density physics, compact X-ray source development, and laboratory astrophysics. Understanding the dynamics of such plasmas requires precise control of their parameters, in particular temperature, on subpicosecond timescales. In this study, X-ray spectral methods were used to diagnose the laser plasma of krypton cluster targets, created at laser pulse intensities of the order of 1020–1021 W/cm2. The use of a time-dependent detailed radiation-collisional kinetic model made it possible to describe the results of the observed X-ray spectra in the femtosecond laser plasma of a cluster target. We present a method for diagnosing the non-stationary plasma of high-atomic-number (krypton) clusters using resonance spectral lines 1s22s22p53s 1P1–1s22s22p6 1S0 and 1s22s22p53s 3P1–1s22s22p6 1S0 of the Ne-like Kr XXVII ion, allowing one to determine the plasma temperature at the moment of “plasma channel” formation. In the experiment, this temperature was shown to be 55 ± 5 eV. The same spectroscopic approach can be extended to other cluster species (for example, Ar, Xe) for non-stationary plasma diagnostics in the relativistic regime.
