Vol. 55 No. 1 Jan-Jun (2009): Revista Mexicana de Física E
Published:
2009-01-01
Artículos
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Complete pure dipole spheroidal electrostatic fields and sources
Abstract:Pure dipole distributions of electric charges on the surfaces of prolate and oblate spheroids are identified from the construction of the respective electrostatic potential and intensity fields, inside and outside the spheroids. The Euler connection between the respective prolate and oblate dipole spheroidal harmonics is emphasized; their transition via the spherical harmonics is also recognized; and their limits of a needle surface and a disk surface, respectively, are readily obtained.⬇️ Scroll down to see the full summary -
Comportamiento periódico en sistemas oscilatorios de una y dos dimensiones
Abstract:In this work, we study the temporal periodic behavior of well-known one and two-dimensional mechanical systems as the vibrating homogenous string, vibrating square membrane and vibrating circular membrane. When an initial configuration of position and velocity of the system is imposed, the temporal evolution of the superposition of the natural modes of vibration is analyzed according to the non-zero Fourier or Bessel-Fourier coefficients. The relations between the temporal frequencies of the normal modes are used to verify the periodicity of the mechanical movement. Numerical results show the temporal evolution of the systems and the periodicity or non-periodicity of the composed movement is verified.⬇️ Scroll down to see the full summary -
Revisión y análisis experimental de modos LP $_{nm}$ en fibras opticas
Abstract:This work shows an experimental study to obtain lineal polarized modes in standard optical fibers (LP$_{nm }$modes). Such modes are getting in a simple set-up, by a mechanical adjustment. In addition, we review the general theory and it is showed computational simulations of such modes. The focus of this work is mainly academic, but at the same time it can be considered basic to start in the fiber optic area.⬇️ Scroll down to see the full summary -
Students' difficulties with tension in massless strings. Part I.
Abstract:Many students enrolled in the introductory mechanics courses have learning difficulties related to the concept of force in the context of tension in massless strings. One of the potential causes could be a lack of functional understanding through a traditional instruction. In this article, we show a collection of this kind of students' difficulties at the New Mexico State University, at the Arizona State University, and at the Independent university of Ciudad Juarez in Mexico. These difficulties were collected during an investigation conducted not only in lab sessions but also in lecture sessions. The first part of the investigation is developed in the contexts of proximity and the length of strings.⬇️ Scroll down to see the full summary -
Propagadores cuánticos calculados de acuerdo con el postulado de Feynman con caminos aproximados por polinomios
Abstract:In this paper we calculate in detail the quantum mechanical propagator for two physical systems, a two-dimensional free particle and a particle in the Earth's gravitational field, according to Feynman sum-over-paths postulate. The method of propagator calculation that we have used is based on an approximation by polynomials, which is consistent with Weierstrass theorem. The results obtained with this method, except for a numerical factor that depend only on the degree of the polynomials, are equal to those obtained through the use of formal methods.⬇️ Scroll down to see the full summary -
The meaning of 1 in j(j+1)
Abstract:The magnitude of the angular momentum ($J^2$) in quantum mechanics is greater than expected from a classical model. We explain this deviation in terms of quantum fluctuations. A standard quantum mechanical calculation gives the correct interpretation of the components of the angular momentum in the vector model in terms of projections and fluctuations. We show that the addition of angular momentum in quantum mechanics gives results consistent with the classical intuition in this vector model.⬇️ Scroll down to see the full summary -
Motion of a falling drop with accretion using canonical methods
Abstract:The motion of a falling drop whose mass grows by accretion is studied with canonical methods. This approach requires the introduction of S-equivalent non natural Lagrangians. That is, we have to consider Lagrangians that give rise to equations of motion that are not exactly the same as the equations of interest, but anyway they share the same solutions. We study three examples of laws of accretion: mass growing linearly with time, mass growing linearly with the surface of the drop, and mass growing proportionally to the product of surface and velocity of the drop. In all cases we recover the results obtained by means of the Newtonian methods, which we expose in table I.⬇️ Scroll down to see the full summary -
Un tratamiento alternativo para el análisis de la colisión elástica bidimensional no relativista entre dos esferas rígidas con parámetro de impacto dado
Abstract:We present a novel treatment for the calculation of the velocities after a two-dimensional elastic collision of two rigid spheres with impact parameter given. For that, we define the collision vector which is invariant under Galilean transformations. The vector gives an alternative form of Newton's collision rule.⬇️ Scroll down to see the full summary -
Revisión del efecto Kerr magneto óptico
Abstract:In this work we review the deduction of Fresnell coefficient for the reflexion of polarized light over a magnetized medium. We obtained the expressions for the Kerr angle in both polar and equatorial case. It is shown that the effect polar magneto-optic effect is two order stronger than the equatorial. This treatment is only valid for magnetic field weaker than 10 T.⬇️ Scroll down to see the full summary -
Digital images of a set of bright shapley ames disk galaxies from San Pedro Mártir glass plates$^{i}$
Abstract:Optical digital images of a set of Shapley Ames disk galaxies are presented. The images were taken originally on glass plates sensitive to blue light, namely, 103aO. The observations on glass plates were obtained mainly to study peculiar circumnuclear structures, crooked spiral arms, peculiar morphology and the identification of possible companions. The glass plates have been scanned and astrometry has been performed in order to determine the position of the brightest central region (compact nucleus) of each galaxy.⬇️ Scroll down to see the full summary -
Generalized treatment for diffusion waves
Abstract:Intended for teaching purposes, the phenomenon of diffusion in the presence of periodical sources is described, taking into account a characteristic operator, $\hat {F}(t)$, leading to a generalized hyperbolic equation. The essential features of the accompanying harmonic flux are presented. For this purpose the solution to the problem is interpreted in terms of diffusion waves, a peculiar class of waves with complex wave numbers whose generation, propagation and detection constitute the basis of modern analytical techniques able to measure optical and transport properties of materials in the condensed or gaseous phase. A generalized mathematical equation describing this kind of waves is shown and the existence of critical modulation frequencies, at which the diffusive fluxes change their behaviour, is demonstrated for different physical phenomena involving diffusion waves. The dispersion equation for diffusion waves is given, and different particular cases in modulation frequency ``spectrum'' are discussed.⬇️ Scroll down to see the full summary -
Entendiendo la relatividad especial usando la frecuencia como concepto esencial
Abstract:The principal consequences of the Special Relativity Theory (SRT) can be deduced considering the frequency measured by different observers (Doppler effect) as well as the postulates of the SRT, with no previous necessity of the Lorentz transformation equations nor the space-time diagrams. If a source located in a system S', that is moving with uniform linear motion with respect to the other system S', emits pulses with frequency $\nu _{0}$ in its proper Reference System (RS), the comparison between the frequencies measured by each observer O' (in S% ') and O (in S) permits to find the effects known as time dilatation and length contraction. Then, by means of a simple algebraic procedure, the Lorentz transformation equations are found.⬇️ Scroll down to see the full summary -
Física computacional: una propuesta educativa
Abstract:Nowadays there exist programming languages whose characteristics make them a very good didactic tool for learning many topics of physics. There are, also, typical learning physical problems that can not be completely explained and even understood using the blackboard, because they present a kind of complex behaviors such as non linearties or many degrees of freedom. That is why they do not have any analytical solution. In any case Computational Physics method is an alternative teaching tool what in practice contains all of the topics of basic programming and numerical methods. In this paper we aboard some issues, enable us, to conform what we will call ``algorithmic education''. We present some traditional physics education problems, based on numerical and visual algorithms, for a better conceptual understanding and models build up by the students it self. Just by using some elementary programming modules, we propose a strategy to build up models starting from a pre-differential conceptual interpretation, which can be particularly useful in the first period of university. The contribution consists in by using a few mathematical elements and resources, students can make more and more complex simulation models. Specifically, for the implementation of the ``algorithmic education´´ we have used python, a programming language what permits the develop of themes covering from the free particle movement, and damped harmonic oscillators, as well as the ideal or hard spheres gases and even Brownian motion walks. In all of these cases the same elementary programming modules have been used.⬇️ Scroll down to see the full summary -
Decay of a quantum discrete state resonantly coupled to a quasi-continuum set of states
Abstract:The irreversible exponential decay from a discrete state to the continuum, described by time-dependent perturbation theory, is a difficult task in quantum mechanics learning, because of the complexity of the mathematical tools involved. An easy model which consists in analyzing the decay from a discrete state to a quasi-continuum set of states is developed. The mathematics required to understand the model are easy, allowing for a deep analysis of the model. The physical conditions required to describe the transition produced by a sinusoidal perturbation by an exponential decay are easily deduced.⬇️ Scroll down to see the full summary -
Students' difficulties with tension in massless strings. Part II
Abstract:Many students enrolled in the introductory mechanics courses have learning difficulties related to the concept of force in the context of tension in massless strings. One of the potential causes could be a lack of functional understanding through a traditional instruction. In this article, we show a collection of this kind of students' difficulties at the New Mexico State University, at the Arizona State University, and at the Independent university of Ciudad Juarez in Mexico. These difficulties were collected during an investigation conducted no only in lab sessions but also in lecture sessions. In this second part of the investigation we show understanding difficulties related to the effect of the angle on tension and the ``compensation arguments''⬇️ Scroll down to see the full summary -
¿Quién era Galileo?
Abstract:Galileo's life and scientific work, has been discussed and analyzed from many points of view. In this paper, the opinions of several authors are presented in order to show their profound divergences, as much in the philosophical as in the historical fields, that Galileo provokes.⬇️ Scroll down to see the full summary
