Showing papers in "European Journal of Physics in 1989"
TL;DR: The case of Ag2S is described in this article, where the existence of intrinsic conduction has been questioned by experimentalists and is verified only by the preparation and investigation of high-purity semiconducting elements.
Abstract: Gray (1731), Desagullier (1742) and Volta (1782) discovered and investigated electric conduction in solids. Davy (1821) found a decrease of the conductivity sigma in metals and Faraday (1833) observed a strong increase with temperature in a number of binary chemical compounds. Hittorf's (1851) measurements on Ag2S and Cu2S led to a linear relation of log sigma against 1/T. The controversial case of Ag2S is described. Hall (1879) and Rowland (1880) discovered a transverse voltage of a current carrying metal film in a magnetic field. Riecke (1901) and Drude (1900) developed the first electron theory of metals and Koenigsberger (1914) tried to explain the temperature dependence of the electrical conductivity by a dissociation theory. Baedeker (1908) was the first to observe semiconducting properties of CuI depending on the stoichiometric composition. Wagner (1933) proved that the conductivity of Ag2S is essentially electronic and not ionic. Gudden (1930) suggested that semiconduction is the result of impurities and imperfections in solids and Wagner and Schottky (1931) developed their theories of lattice defects (Fehlordnungs-Erscheinungen). Wilson (1931) presented the first band theory of intrinsic and extrinsic semiconductors. The existence of intrinsic conduction has been questioned by experimentalists and is verified only by the preparation and investigation of high-purity semiconducting elements.
45 citations
TL;DR: In this article, an advanced undergraduate experiment on the chaotic behaviour of a dripping faucet is presented, which can be used for the demonstration of typical features of chaotic phenomena and also allows the advanced physics student to learn about the use of microcomputers as data-taking devices.
Abstract: An advanced undergraduate experiment on the chaotic behaviour of a dripping faucet is presented. The experiment can be used for the demonstration of typical features of chaotic phenomena and also allows the advanced physics student to learn about the use of microcomputers as data-taking devices. For convenience a brief introduction to the basic concepts of nonlinear dynamics and to the period-doubling route to chaos are included.
33 citations
TL;DR: In this article, the acoustic modes of a corrugated tube open at both ends and rotating in a plane were examined as a function of rotational frequency and found to be similar but not identical to those of a stationary open-ended organ pipe.
Abstract: A simple, yet unusual, child's toy illustrates some basic features of the physics of resonance, waves and fluid dynamics. The acoustic modes of a corrugated tube open at both ends and rotating in a plane were examined as a function of rotational frequency and found to be similar but not identical to those of a stationary open-ended organ pipe. Measurements of the pressure difference at resonance across the tube ends as a function of rotational frequency agree well with a simple analysis based on Bernoulli's principle. A mechanism of sound production is proposed whereby the tube resonantly amplifies acoustic perturbations to the axial air flow, engendered by the corrugations, that occur at frequencies equal to the resonant frequencies of the tube. The mechanism is supported by direct measurements of the axial air speed as a function of rotational frequency.
24 citations
TL;DR: In this article, a two-way moving sidewalk is used to illustrate relative velocity, time dilation, and length contraction of the theory of special relativity on a rotating disc model.
Abstract: Some classical thought experiments in special relativity are performed on a two-way moving sidewalk. Since each of the two sides moves at constant speed, this device provides a simple, intuitive way to illustrate relative velocity, time dilation, and length contraction. It should therefore allow for a better understanding of the basic concepts of the theory. Furthermore, being a closed system the two-way sidewalk exhibits some of the characteristics of a rotating disc, and might therefore be helpful in an introduction to general relativity.
17 citations
TL;DR: In this article, a simple quaternion expression for the quantum mechanical four-current of a single particle was proposed, and it was shown that the equation of continuity is obeyed and the behaviour under a Lorentz transformation is correct.
Abstract: A simple quaternion expression is proposed for the quantum mechanical four-current of a single particle. It is shown that the equation of continuity is obeyed and the behaviour under a Lorentz transformation is correct. The expression is almost equivalent to that emanating from the Dirac theory. It differs, however, from those of other authors who have considered the quaternion formulation of relativistic quantum mechanics.
16 citations
TL;DR: In this paper, the changes of entropy taking place in a quantum system during a measurement process are reviewed, with a view to clarifying the concepts of entropy, information and quantum measurement.
Abstract: The changes of entropy taking place in a quantum system during a measurement process are reviewed, with a view to clarifying the concepts of entropy, information and quantum measurement. It is shown that a non-negative amount of information is gained in spite of the loss of information (or entropy increase) caused by the reduction of the wavepacket.
13 citations
TL;DR: An electron in the hydrogen atom would suffer a shift in the frequency of transition from one quantum state to another if it obeyed a discrete time Schrodinger equation as discussed by the authors, in principle, could be measured if resolution beyond the hyperfine structure could be made.
Abstract: An electron in the hydrogen atom would suffer a shift in the frequency of transition from one quantum state to another if it obeyed a discrete time Schrodinger equation. This shift, in principle, could be measured if resolution beyond the hyperfine structure could be made.
13 citations
TL;DR: In this paper, the origin and physical interpretation of boundary conditions for a free particle confined to a half-line is investigated. But the authors consider the case where the free particle is bounded by a half line.
Abstract: The origin and the physical interpretation of boundary conditions for a free particle confined to a half-line are analysed. The authors consider potentials V(x,a, . . .) (depending upon parameters a, . . . and x in (- infinity , + infinity )) for which solutions psi (x,a, . . ., t) of the corresponding Schrodinger equation reduce, in a suitable limit a from a0, . . ., to solutions psi (x,t) of the Schrodinger equation for a free particle confined to a half-line satisfying the boundary condition ( delta psi / delta x)(x=0, t)=a psi (x=0, t) with real alpha = alpha (a0, . . .).
11 citations
TL;DR: In this paper, the authors report the results of their investigations of the Kelvin generator under various controlled conditions with both nonpolar and polar liquids and a sodium chloride aqueous solution and propose a model in which the electric charge results from the separation of the hydrogen and hydroxyl ions as the water droplets form.
Abstract: The Kelvin generator is an amazing electrostatic device which poses many questions. The authors report the results of their investigations of this device under various controlled conditions with both nonpolar and polar liquids and a sodium chloride aqueous solution. They have found that the generator works well even if the two liquid streams originate from different electrically insulated reservoirs. In addition they propose a model in which the electric charge results from the separation of the hydrogen and hydroxyl ions as the water droplets form.
9 citations
TL;DR: In this article, a simple and inexpensive apparatus is described which allows fast and reliable measurements to be made of the temperature dependence of the electrical conductivity in a semiconductor sample, and the energy gap can be calculated from the data taken in the intrinsic region.
Abstract: A simple and inexpensive apparatus is described which allows fast and reliable measurements to be made of the temperature dependence of the electrical conductivity in a semiconductor sample. The energy gap can be calculated from the data taken in the intrinsic region, and the temperature dependence of the majority carrier mobility can be deduced from measurements taken in the extrinsic region.
9 citations
TL;DR: In this article, a fresh look at the old topic of the accelerated observer in the context of special relativity is taken, with particular attention to photon trajectories which are shown to be circular arcs, whereas free material particles move in elliptic arcs.
Abstract: Prompted by a newspaper report of plans for space travel, a fresh look is taken at the old topic of the accelerated observer in the context of special relativity. General relations are illustrated by the case of uniform acceleration, with particular attention to photon trajectories which are shown to be circular arcs, whereas free material particles move in elliptic arcs. Doppler-type relations exhibit dependence on the acceleration of the observer intermingled with the velocity of a source or reflector of light.
TL;DR: The relation of the Ampere form, d2F12=( mu 0/4 pi )I1I2(3(dr1.r12/r12)-2(dr 1.dr2))r12 /r123, to the Biot-Savart, or Grassmann form is revisited from time to time as mentioned in this paper.
Abstract: The relation of the Ampere form, d2F12=( mu 0/4 pi )I1I2(3(dr1.r12/r12)(dr2.r12/r12)-2(dr1.dr2))r12/r123, to the Biot-Savart, or Grassmann form, d2F12=( mu 0/4 pi )I1I2dr2 V-product (dr1 V-product r12)/r123, of the law for the force between current elements is revisited from time to time. Recently experiments were reported to support the claim that the two forms are not equivalent. One hundred and twenty years ago J. Stefan (1869) answered most of the questions which reappear in contemporary work. Though the paper is seldom quoted it is instructive even today.
TL;DR: In this article, the Lagrangian formalism was used to show the close relationship between the classical mechanics of the harmonic oscillator and the ray optics of the parabolic index optical waveguide.
Abstract: For pt.I see ibid., vol.10, p.136-43 (1989). In the preceding paper the authors used the Lagrangian formalism to show the close relationship between the classical mechanics of the harmonic oscillator and the ray optics of the parabolic index optical waveguide. The authors have now studied the corresponding quantum mechanical and wave optical problems and, in particular, have studied the time evolution of a coherent state and have shown its close relationship to the propagation of a Gaussian beam in a parabolic index optical waveguide. The corresponding transitions to classical mechanics and ray optics have been shown. The authors have also presented an analysis of the recently developed squeezed states and have shown its correspondence to the waveguide problem. They have demonstrated that the relationship between classical and quantum mechanics is the same as between ray optics and wave optics. All such analyses should be of considerable pedagogical value.
TL;DR: In this paper, the Lagrangian formalism was used to study the relationship between the harmonic oscillator problem and the propagation of a Gaussian beam in a parabolic index optical waveguide.
Abstract: The authors discuss the harmonic oscillator problem in the domains of classical mechanics and the parabolic index optical waveguide problem in the domains of ray optics. While discussing the classical mechanics and the ray optics of the two problems the authors have used the Lagrangian formalism which allows them to see the close relationship between the two problems. In part II of the paper the authors study the corresponding quantum mechanical and wave optical problems. In particular whilst looking at the time evolution of a coherent state the authors demonstrate that it has a close relationship to the propagation of a Gaussian beam in a parabolic index optical waveguide.
TL;DR: The missing solar neutrino problem as discussed by the authors has been studied for 30 years and has led to speculations about physics beyond the Standard Model of electroweak interactions, such as whether neutrinos are massive and undergo flavor oscillations and whether they have detectable electromagnetic moments.
Abstract: Part of the interest in neutrino astrophysics has to do with the fascinating interplay between nuclear and particle physics issues — e.g. whether neutrinos are massive and undergo flavor oscillations, whether they have detectable electromagnetic moments, etc. — and astrophysical phenomena, such as the clustering of matter on large scales, the processes responsible for the synthesis of nuclei, the mechanism for core-collapse supernovae and the evolution of our sun. This summary addresses one of the oldest problems in neutrino astrophysics, the 30 year puzzle of the missing solar neutrinos. This puzzle grew out of attempts to test the standard theory of main-sequence stellar evolution, but has now led to speculations about physics beyond the Standard Model of electroweak interactions. I shall describe the work that defined the solar neutrino problem, the likelihood that its resolution is connected with massive neutrinos and the hopes we have for future experiments.
TL;DR: In this article, the charging time for grains of micrometre size is studied theoretically with some selected parameters to match the environment of space plasmas and two models are considered: when the grain is isolated and when grain density increases so that the spherical capacitor model and consequently the intersection of the grain Debye spheres is applied.
Abstract: The charging time for grains of micrometre size is studied theoretically with some selected parameters to match the environment of space plasmas Two models are considered: when the grain is isolated and when the grain density increases so that the spherical capacitor model and consequently the intersection of the grain Debye spheres is applied The analysis shows that for both models the charging time is a strong function of plasma electron temperature The proximity of the neighbouring grains has an effect on both the grain capacitance and the potential difference due to the depletion of the electron population in the plasma There is one value for the characteristic grain separation at which the charging time is the same for selected values of the grain charge, and there is also an inversion point at a certain value of the grain charge
TL;DR: In this paper, an updated derivation of the equations describing the Poynting-Robertson effect is presented for the case of a point-like emitter, and it is shown explicitly that the drag force is originated solely during the absorption process.
Abstract: An updated derivation of the equations describing the Poynting-Robertson effect is presented for the case of a point-like emitter. It is shown explicitly that the drag force is originated solely during the absorption process. The problem is further generalised to the new, and more realistic, situation in which the source is extended and in rotation.
TL;DR: The mechanism of optical echo (photon echo) formation in solid and gas media is described in this paper, based on solutions of Schrodinger's equation for the time evolution of atomic amplitudes during an optical excitation pulse sequence, and should be accessible to non-specialists and to students studying undergraduate quantum mechanics.
Abstract: The mechanism of optical echo (photon echo) formation in solid and gas media is described. The treatment is based on solutions of Schrodinger's equation for the time evolution of atomic amplitudes during an optical excitation pulse sequence, and should be accessible to non-specialists and to students studying undergraduate quantum mechanics. Atomic amplitude evolution diagrams are developed to facilitate the analysis of the echo mechanism and the derivation of the echo time and propagation direction.
TL;DR: In this article, a simple theory based on the Rayleigh method is presented for the frequencies of the in-plane modes of a thin circular ring which is clamped at one point.
Abstract: A simple theory based on the Rayleigh method is presented for the frequencies of the in-plane modes of a thin circular ring which is clamped at one point. The predictions of this theory are compared with experiment. A novel method for the determination of Young's modulus for material in the form of a ring is described; this method involves an extrapolation to the behaviour for the high-order modes and is not dependent on a full knowledge of the equation governing the vibration frequencies.
TL;DR: In this paper, the authors discuss some misconceptions concerning the status and significance of specific heat in black-body radiation in equilibrium and provide an extension list of references to indicate the various positions adopted by different authors on this issue.
Abstract: Discusses some misconceptions concerning the status and significance of specific heat in black-body radiation in equilibrium. An extension list of references is provided to indicate the various positions adopted by different authors on this issue. The way in which simple mathematical manipulation of thermodynamic formulae may lead to unphysical results for radiation in equilibrium is indicated and a consistent derivation and interpretation of the specific heat for black-body radiation is presented.
TL;DR: In this article, the classical theory of a charged particle is revisited in the case where the particle has angular momentum, so that it is endowed with a magnetic moment as well as with an electric charge.
Abstract: The classical theory of a charged particle is revisited in the case where the particle has angular momentum, so that it is endowed with a magnetic moment as well as with an electric charge. The resulting electromagnetic field contributes to the mass and spin of the particle, which are both to be renormalised. Discussing this effect leads to modifying the traditional ideas concerning the 'classical radius' of the electron, and to proposing a classical estimate of radiative corrections to the gyromagnetic factor, so that a better consistency with quantum views is achieved.
TL;DR: In this article, the unbounded motions of a swinging Atwood's machine are analyzed by blowing up the singularity at infinity and the asymptotic motion is reduced to a gradient flow on an ellipsoid.
Abstract: The unbounded motions of a swinging Atwood's machine are analysed by blowing up the singularity at infinity The asymptotic motion is reduced to a gradient flow on an ellipsoid By studying the flow on this ellipsoid it is shown that the unbounded orbits oscillate either an infinite number of times or not at all, depending only on a critical value of the mass ratio
TL;DR: In this article, a demonstration based on the Meissner effect presented by the new high-Tc superconductors is described, which requires equipment commonly available in a physics or chemistry laboratory.
Abstract: A demonstration based on the Meissner effect presented by the new high-Tc superconductors is described. The experiment requires equipment commonly available in a physics or chemistry laboratory. The high Tc superconducting tablets can be produced in an inexpensive furnace. Under the experimental conditions, the levitating magnet turns out to be extremely sensitive to small variations in the magnetic field intensity; therefore, the experimental arrangement could possibly be used as a magnetometer. The controllable rotation frequency of the magnet suggests that the same arrangement may be used as a specimen manipulator in a piece of equipment where the rotation of the samples is of importance.
TL;DR: In this article, the authors define and investigate the current usage of computers within university departments of physics by outlining the chronology of their introduction and their role in the new subject of computational physics.
Abstract: For many years now the education of physicists has been limited by the necessity of restricting classroom attention to stylistic examples and laboratory attention to fairly cheap and limited exercises. The introduction of the computer into the classroom and laboratory removes these constraints and in turn permits the training of a new breed of computational physicists. The authors define and investigate the current usage of computers within university departments of physics by outlining the chronology of their introduction and their role in the new subject of computational physics.
TL;DR: It is possible to display large stroboscopic images and to derive other data from them, such as time derivatives and distribution functions, as well as to collect and analyse motion data.
Abstract: A simple and versatile method to collect and analyse motion data is described. A video camera is focused on a bright spot attached to an object, and an appropriately adapted computer performs the display and further processing. Thus it is possible to display large stroboscopic images and to derive other data from them, such as time derivatives and distribution functions. As illustrative examples a few standard experiments are described (ballistic curves. movement on an air track, oscillations, collisions, statistical motion).
TL;DR: In this article, a method for visualizing electronic densities is derived directly from the definition of position probability density, which is based on the generation of a random cloud of points so that the density of points at a given position is equal to the electronic density at that position.
Abstract: A method for visualising electronic densities is derived directly from the definition of position probability density. It is based on the generation of a random cloud of points so that the density of points at a given position is equal to the electronic density at that position. There are three main advantages to this approach: (a) it allows one to view the inner parts of the electronic distribution, (b) the rotation of the graph is easily accomplished using this method and (c) the overall visual impression is the closest that can be obtained to reality. A set of FORTRAN 77 subroutines is given, which has been applied for drawing hydrogen-like and hybrid orbitals.