Sang Ho Sohn

In recent years, interest in rockets and artificial satellites mounted on rockets has been growing, with floating space debris a cause for special concern. Rock In recent years, interest in rockets and artificial satellites mounted on rockets has been growing, with floating space debris a cause for special concern. Rock

A parallel plate capacitor’s structure consists of conducting plates arranged parallel to each other. Various experiments related to the storage of electric cha A parallel plate capacitor’s structure consists of conducting plates arranged parallel to each other. Various experiments related to the storage of electric cha

Galileo observed free-fall motion and estimated the magnitude of g in the late 1500s1; free-fall experiments continue to be widely used for measuring g in Galileo observed free-fall motion and estimated the magnitude of g in the late 1500s1; free-fall experiments continue to be widely used for measuring g in

In this study, we derived formulas for the current waveforms induced by a magnet oscillating at arbitrary positions on the axis of a solenoid. We also conducted an experiment for measuring the currents induced in a solenoid by a magnet oscillating in its inner or outer region and compared the results with theoretical predictions. It was confirmed that the magnitude and shape of waveforms of induced currents that were obtained from the derived formulas fit well with experimental results. In addition, the magnetic drag force exerted on the magnet by the induced current is formulated and compared with the prediction estimated by the attenuation coefficient and velocity.

In this study, formulae for the waveform of an induced current, I t , generated when a magnet traverses along a rectangular coil with a narrow width were theoretically obtained considering the relative motion of the magnet and coil. Consequently, an experiment was performed under experimental conditions that matched the formulas, and the results obtained were compared with the theoretical predictions. The dependence of I ( t ) on the initial angle ϕ 0 of the magnet pendulum and the width w of the rectangular coil was found to be consistent with the theoretical prediction. Thus, the formulae obtained in this study are expected to be useful in addressing temporal variations in the waveform of the induced current produced by a magnet moving in a polar coordinate space.

A solenoid is a coil wound many times on a cylinder of length greater than its diameter. Solenoids are mainly used as electromagnets, because a magnetic field is formed when current flows through a solenoid. The solenoid described in secondary school and university textbooks is a single-layered solenoid. Further, textbooks and papers focusing on education primarily describe the magnetic fields caused by infinite solenoids. However, most solenoids used in laboratory or daily life are finite solenoids with multiple layers to achieve a strong magnetic field. Examples include solenoid valves, Faraday rotators, and modulators.

The Mariotte bottle is a device that delivers a constant flow rate as a result of the constant pressure inside the bottle. This bottle has also been used to study Torricelli’s law, the transition of laminar and turbulent flow, and the capillary interruption of a liquid jet. In fluid mechanics, orifice hydraulic coefficients are essential prerequisites for determining the actual flow of fluid through the orifice. As is well known, when determining the discharge and velocity coefficients of a fluid emitted from a cylinder, maintaining a constant head by continuously supplying the fluid according to the flow rate is difficult.

In this study, we derived several formulas for the currents induced in a circular loop by a magnet connected to a spring-based simple harmonic oscillation system. In addition, we conducted an experiment for measuring the induced currents and compared the results with the theoretical prediction. It was confirmed that the prediction from the derived formulas fits well with experimental results. Via derived formulas and a simple experiment, Faraday’s Law and Lenz’s Law could be easily explained.

The capacitor is a device that can store an electric charge and has a structure with two insulated electrode plates. When a voltage is applied to the capacitor, electric charge accumulates on the plates; current flows during the charge accumulation but does not flow when the charge accumulation is complete. Dielectric inserts are made from a substance that generates a dielectric polarization when an electric field is applied to them. The capacitance C of a parallel plate capacitor filled with dielectric material can be expressed as:

To improve its light conversion efficiency, NaYF₄:(Yb³⁺, Er³⁺) upconversion (UC) phosphor, which generates one visible photon by absorbing two or more near‐infrared photons, was coated with SiO₂ nanoparticles. The surface modification of phosphor was performed by using a modified sol–gel method as a function of the concentration of colloidal silica employed as the surface coating precursor. It was found that the PL intensities depend on the concentration of colloidal silica. When a 2.7 wt% concentration of colloidal silica was used, the NaYF₄:(Yb³⁺, Er³⁺) phosphor exhibited a homogeneous coating with silica and an approximately 9% increase in the PL intensity, as compared with that of the non‐coated sample of NaYF₄:(Yb³⁺, Er³⁺) phosphor. This increase in the PL intensity can be explained by the suppression of the nonradiative recombination of electron–hole pairs via surface defects. The experimental results suggest that the surface modification of upconversion phosphors with a silica coating of the appropriate concentration is a simple and effective solution to improve the light conversion efficiency of upconversion phosphors used in optoelectronic devices.