Horseshoe Magnet Research Articles

Fading force

My horseshoe magnet isn't as strong as it once was. Does magnetism decay over time, like radioactivity?

Fading force

My horseshoe magnet isn't as strong as it was. Does magnetism decay over time, like radioactivity? Alan Moskwa, Adelaide, South Australia

Magnetic fields produced by non-concentric and non-coplanar currents in circular loops

A numerical calculation for the stationary magnetic field produced by arrangements of non-concentric and non-coplanar loop current circuits is presented. The calculation is done by superposing the solution of the magnetic field produced by a set of loops with constant currents that mimic two and three-dimensional systems. In the three-dimensional cases, this is achieved by rotating the magnetic field produced by the non-coplanar loops and adding all the contributions at any arbitrary point in the space. We report the case of two coplanar non-concentric loops that do not overlap and two concentric coplanar rings with different radii carrying currents in the same and opposite directions. Then we consider two non-coplanar rings that are tilted by an angle. More complicated systems consist of a set of loops forming a semi-doughnut. As an extension, we add at the two ends of this system concentric loops to form a horseshoe magnet with a circular cross-section and analyze the results as a function of its geometric characteristics. We can calculate the solutions of the magnetic field in all the space and plot their field lines using a technique that makes use of the Runge–Kutta fourth-order method. In all the cases we plot with different colors the field lines to give information on their strength.

Modeling of non-ideal hard permanent magnets with an affine-linear model, illustrated for a bar and a horseshoe magnet

This study is dedicated to continuum-scale material modeling of isotropic permanent magnets. An affine-linear extension to the commonly used ideal hard model for permanent magnets is proposed, motivated, and detailed. In order to demonstrate the differences between these models, bar and horseshoe magnets are considered. The structure of the boundary value problem for the magnetic field and related solution techniques are discussed. For the ideal model, closed-form analytical solutions were obtained for both geometries. Magnetic fields of the boundary value problems for both models and differently shaped magnets were computed numerically by using the boundary element method. The results show that the character of the magnetic field is strongly influenced by the model that is used. Furthermore, it can be observed that the shape of an affine-linear magnet influences the near-field significantly. Qualitative comparisons with experiments suggest that both the ideal and the affine-linear models are relevant in practice, depending on the magnetic material employed. Mathematically speaking, the ideal magnetic model is a special case of the affine-linear one. Therefore, in applications where knowledge of the near-field is important, the affine-linear model can yield more accurate results—depending on the magnetic material.

Design of Experimental Apparatus for Asynchronous Motor Principle

Current domestic and international for the experimental apparatus been associated asynchronous motor design generally used hand horseshoe magnet rotates to drive the rotor rotates, While it is possible to achieve, the apparatus is too simple, and the effect is not in great satisfaction. To further improve the experimental results, a new type of asynchronous motor experimental device is designed, whose working mechanism is a DC motor as a driving source, driven by a reduction gear mechanism to produce a rotating magnetic field, the control circuit can be achieved by utilizing the rotational speed and adjust direction. By apparatus of the stator, rotor apparatus, the related motor control and display device design can make the operation more stable, more easily observed. The experimental apparatus can enhance students' awareness and understanding of asynchronous motor, so that the original abstract theory becomes boring incomprehensible gusto, to stimulate students' desire for knowledge, strengthen students' practical knowledge and ability, with higher practical significance. The apparatus simple shaped, with simple and safe operation, is able to facilitate teaching, with better promote the use of value.

Pulse speed on a plucked wire

This paper serves to update an elegant experiment published in The Physics Teacher to measure the speed of a pulse on a taut metal wire.1 Unfortunately, commercially available units2 that serve the same purpose are priced outside the range of most high school or college physics teaching laboratories. Wakeland et al. show how an affordable adaptation of the traditional standing wave apparatus using taut metal wire and horseshoe magnets can be used to measure the speed of a pulse by using an oscilloscope to measure an induced voltage in the wire as the pulse transverses the middle of the magnets, which are a known distance apart.

The embryonic and post-embryonic development in two Drosophila species exposed to the static magnetic field of 60 mT

In this study, a static magnetic field influence on development and viability in two different species, Drosophila melanogaster and Drosophila hydei, was investigated. Both species completed development (egg–adult), in and out of the static magnetic field induced by double horseshoe magnet. Treated vials with eggs were placed in the gap between magnetic poles (47 mm) and exposed to the average magnetic induction of 60 mT, while control ones were kept far enough from magnetic field source. We found that exposure to the static magnetic field reduced development time in both species, but statistical significance was found only for D. hydei. Furthermore, we found that the average viability of both Drosophila species exposed to the magnetic field was significantly weaker compared to control ones. These results indicate that 60 mT static magnetic field could be considered as a potential stressor, influencing on different levels the embryonic and post-embryonic development of individuals.

FlareLab: early results

The FlareLab experiment at Bochum University has been constructed to generate and investigate plasma-filled magnetic flux tubes similar to arch-shaped solar prominences, which often result in coronal mass ejections (CMEs). In its first version, the device has been used to reproduce and extend previous studies of Bellan et al (1998 Phys. Plasmas 5 1991). Here the plasma source consists of two electrodes, which can be connected to a 1.0 kJ capacitor bank, and of a horseshoe magnet, which provides an arch-shaped guiding field. The discharge is ignited in a cloud of hydrogen gas that has been puffed into the space above the electrodes. In the first few microseconds the plasma current rises at a rate of several kA µs−1, causing the plasma column to pinch along the guiding B-field and to form an expanding loop structure. The observed dynamics of the magnetic flux tubes is analysed by means of three-dimensional MHD simulations in order to determine the influence of parameters like the initial magnetic field geometry on magnetic stability. At present, FlareLab is redesigned to mimic a model that was proposed by Titov and Démoulin (1999 Astron. Astrophys. 351 707) to investigate twisted magnetic configurations in solar flares.

Apparatus to study the onset of free convection about vertical and inclined hot wires

This article describes a methodology and an apparatus used to evaluate the onset time of free convection in hot-wire experiments. The evaluation of the onset time is useful to obtain a measurement interval that is suitable to estimate the thermal properties of a fluid. If a pure conduction regime is present, the hot-wire temperature increment versus time is a straight line in a semilog plot, whereas the convection effect induces a deviation from this trend. An algorithm based on the F test is proposed to evaluate the onset time of free convection. The experimental facility has the particular feature of allowing an easy change of the hot-wire inclination angle up to 118.3 mrad. The wire is kept in a tilted position by a permanent horseshoe magnet, and the tilting angle from the vertical is measured by a theodolite. Some testing results using water are discussed for vertical and inclined wires. A good agreement between the experimental onset times and the theoretical ones is found in the case of a vertical wire.

Torsional Oscillations with Lorentz Force

We have built a device that uses the Lorentz force on a current-carrying wire situated in a magnetic field, F = I L × B, in order to demonstrate a slowly varying alternating current by means of an optical lever. The apparatus consists of a horseshoe magnet, a length of thin enamel-coated wire (ours was 0.3 mm thick), a signal generator, a rheostat, and a laser. Construction is illustrated in the diagram (Fig. 1).

Magnetic oscillation of crystal without spontaneous moment caused by single-ion anisotropy achieved by a horseshoe magnet above 1000 K

Temperature dependence of anisotropy of magnetic susceptibility Δ χ was studied up to T=1000 K for various oxide crystals using a method based on field-induced rotational-oscillation of a sample; Δ χ– T relationships followed the Curie–Weiss law for muscovite, talc, Mg(OH) 2, Al(OH) 3, AlOOH orthoclase and corundum. The Δ χ-values are above 10 −7 emu/g at T=1000 K for many of the measured oxides; spontaneous magnetic moments due to spin ordering are usually lost at this temperature. This magnitude of Δ χ is large enough for micro-crystals, which are dispersed in fluid medium, to be aligned below B=1 T that can be produced by a permanent magnet. Alignment at low field intensity is effective to extend various field-induced materials processing at high temperatures, for example, crystal growth of high quality.

Symmetry in electromagnetism—A new magnetic needle

Students frequently are introduced to Oersted’s experiment by deflecting a plotting compass beneath a straight current-carrying conductor. Thereafter, electromagnets, electric bells, relays, and motors are explored. When attention is turned to electromagnetic induction, the usual setup involves thrusting a straight wire between the jaws of a powerful horseshoe magnet. To help underline the symmetry involved, we have developed a stronger magnetic needle and outline here how we use it in our classes.

Investigating refrigerator magnets

Two articles recently carried in The Physics Teacher have included discussions of “refrigerator magnets.” These articles have been informative, and I would like to add the simple analogy of a horseshoe magnet to the discussion. After all, a horseshoe magnet is a “one-sided” magnet in that it has the effective part of its field only on the end where the poles are, whereas the end with the U-bend provides little useful magnetic force.

Everyone's Magnetism

If you were to tell a child playing with a horseshoe magnet and pieces of iron that his uncle has a much bigger magnet that can lift everything and everybody, the child would probably believe you and might even ask for a ride on the magnet. If a physicist were present at such a conversation, he or she—armed with knowledge and experience—would probably smile condescendingly. The physicist would know well that only a very few materials—such as iron or nickel—are strongly magnetic, while the rest of the world's materials are not; to be precise, the rest of the world is a billion (109) times less magnetic. This number seems obviously too large to allow common substances (water, for example) to be lifted even by the most powerful magnets; a billionfold increase in magnetic fields can be found only on neutron stars. In this case, however, knowledge and experience would mislead the physicist: In fact, all materials can be lifted by using magnetic fields that are rather standard these days. In principle, even a child can be levitated by a magnet, as we shall see below.

Fiberoptic Intracranial Pressure Monitoring during Magnetic Resonance Imaging

Fiberoptic Intracranial Pressure Monitoring during Magnetic Resonance Imaging

Magnetic damping: Analysis of an eddy current brake using an airtrack

A simple theory is proposed using Faraday’s law and the Lorentz force to analyze the effect of magnetic damping on an aluminum plate moving on a horizontal air track as it passes between the poles of a horseshoe magnet. The position, velocity, and acceleration of the nonmagnetic conducting plate are measured as a function of time using a motion detector. Using some simplifying assumptions, a theoretical model is obtained in which a single free parameter is used to fit the experimental data. This parameter corresponds to an effective length (LR) in which the eddy current encounters resistance as it moves around a closed path in the conductor. This leads to some interesting, but unexpected, results about the shape and magnitude of induced eddy currents.

Angle-resolved inverse photoemission spectroscopy with longitudinally spin-polarized electrons

We have built and tested a spin-polarized electron source based on photoemission from negative electron affinity GaAs(100). It provides 5–10 μA of longitudinally spin-polarized electrons in the energy range 5–20 eV. Following the design of Erdman and Zipf, the electron optics are simple and consist of only five elements. Their voltages are all proportional to each other and are linearly driven by one ramping voltage. The spin-polarized electrons are used for angle-resolved inverse photoemission measurements from magnetized sample surfaces. Our first results obtained from Ni(110) mounted on a horseshoe magnet agree well with the literature. From these measurements the degree of spin polarization is determined to be 35%±5%. We also checked the spin polarization using an absorbed-current spin detector in combination with a 90° cylindrical deflector.

Magnetic Field Reconstruction by CT Technique

Computer tomography techniques were used to obtain cross-sectional images of a magnetic field. A conducting wire was passed through the field at constant velocity and at a series of orientations (in 3° increments) with respect to a horseshoe magnet, and the resulting induced voltages used as projection data to extract two-dimensional tomographic images of the vertical component of the magnetic field of the magnet.

Coilless magnetic pickup for stringed instrument

A magnetic pickup for an electronic amplification system of a stringed musical instrument wherein the variable electrical signal produced in response to the string traversing the lines of flux from a permanent magnet is generated by a Hall effect sensor, thereby eliminating the usual inductively coupled coil(s). The invention is disclosed in embodiments employing bar and horseshoe magnets with the sensor positioned on the opposite or on the same side of the magnet as the string. The sensor is an essentially planar device which may be positioned in a plane substantially normal to the lines of flux in contact with or spaced a predetermined distance from the associated magnet or positioned in a plane non-perpendicular to the lines of flux, or adjustably positioned with respect to the direction of flux lines to achieve the desired degree of sensitivity.

Some preliminary studies of the effects of a static magnetic field on the life cycle of the Lebistes reticulatus (guppy)

Lebistes reticulatus (guppy) was subjected to a continuous treatment of a 500-G homogeneous magnetic field within a specially designed horseshoe magnet encompassing a small aquarium. The experiment was carried through several generations with the following results: in the first generation, the brood size was normal but the gestation period was reduced by 30%; the second generation had an average reduction of spawn rate of 50% and a reduction of the gestation period of 30%; and in the third generation, reproduction was completely inhibited as long as the fish remained within the magnetic field.