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The Einstein-de Haas effect, or the Richardson effect (after Owen Willans Richardson), is a physical phenomenon delineated by Albert Einstein and Wander Johannes de Haas in Germany in the mid 1910's. Sir Owen Willans Richardson ( April 26, 1879 - February 15, 1959) was a British Physicist, professor at Princeton Albert Einstein ( German: ˈalbɐt ˈaɪ̯nʃtaɪ̯n; English: ˈælbɝt ˈaɪnstaɪn (14 March 1879 – 18 April 1955 was a German -born theoretical Wander Johannes de Haas ( March 2, 1878, Lisse – April 26, 1960, Bilthoven) was a Dutch Physicist and

Contents

Description

The effect corresponds to the mechanical rotation that is induced in a ferromagnetic material (of cylindrical shape and originally at rest), suspended with the aid of a thin string inside a coil, on driving an impulse of electric current through the coil. Ferromagnetism is the basic mechanism by which certain materials (such as Iron) form Permanent magnets and/or exhibit strong interactions with Magnets it A coil is a series of loops A coiled coil is a structure where the coil itself is in turn also looping Electric current is the flow (movement of Electric charge. The SI unit of electric current is the Ampere. To this mechanical rotation of the ferromagnetic material (say, iron) is associated a mechanical angular momentum, which, by the law of conservation of angular momentum, must be compensated by an equally large and oppositely directed angular momentum inside the ferromagnetic material. Iron (ˈаɪɚn is a Chemical element with the symbol Fe (ferrum and Atomic number 26 In Physics, the angular momentum of a particle about an origin is a vector quantity equal to the mass of the particle multiplied by the Cross product of the position In Physics, the angular momentum of a particle about an origin is a vector quantity equal to the mass of the particle multiplied by the Cross product of the position Given the fact that an external magnetic field, here generated by driving electric current through the coil, leads to magnetisation of electron spins in the material (or to reversal of electron spins in an already magnetised ferromagnet — provided that the direction of the applied electric current is appropriately chosen), the Einstein-de Haas effect demonstrates that spin angular momentum is indeed of the same nature as the angular momentum of rotating bodies as conceived in classical mechanics. In Physics, a magnetic field is a Vector field that permeates space and which can exert a magnetic force on moving Electric charges Magnetization is defined as the quantity of Magnetic moment per unit volume The electron is a fundamental Subatomic particle that was identified and assigned the negative charge in 1897 by J In Quantum mechanics, spin is a fundamental property of atomic nuclei, Hadrons and Elementary particles For particles with non-zero spin Classical mechanics is used for describing the motion of Macroscopic objects from Projectiles to parts of Machinery, as well as Astronomical objects This is remarkable, since electron spin, being quantized, cannot be described within the framework of classical mechanics. In Physics, quantization is a procedure for constructing a Quantum field theory starting from a classical field theory.

Commenting on the papers by Einstein, Calaprice in The Einstein Almanac writes:[1]

52. [A. Einstein, W. J. de Haas,] Experimenteller Nachweis der Ampereschen Molekularstörme [Experimental Proof of Ampère's Molecular Currents], Deutsche Physikalische Gesellschaft, Verhandlungen 17 (1915): 152-170.

Considering Ampère's hypothesis that magnetism is caused by the microscopic circular motions of electric charges, the authors proposed a design to test Lorentz's theory that the rotating particles are electrons. André-Marie Ampère (20 January 1775 &ndash 10 June 1836 was a French Physicist and Mathematician who is generally credited as one of the main discoverers Hendrik Antoon Lorentz ( July 18, 1853 &ndash February 4, 1928) was a Dutch Physicist who shared the 1902 Nobel The aim of the experiment was to measure the torque generated by a reversal of the magnetisation of an iron cylinder. A torque (τ in Physics, also called a moment (of force is a pseudo- vector that measures the tendency of a force to rotate an object about

Calaprice further writes:

53. [A. Einstein, W. J. de Haas,] Experimental Proof of the Existence of Ampère's Molecular Currents (in English), Koninklijke Akademie van Wetenschappen te Amsterdam, Proceedings 18 (1915-16).

Einstein wrote three papers with Wander J. de Haas on experimental work they did together on Ampère's molecular currents, known as the Einstein-de Haas effect. Wander Johannes de Haas ( March 2, 1878, Lisse – April 26, 1960, Bilthoven) was a Dutch Physicist and André-Marie Ampère (20 January 1775 &ndash 10 June 1836 was a French Physicist and Mathematician who is generally credited as one of the main discoverers He immediately wrote a correction to paper 52 (above) when Dutch physicist H. A. Lorentz pointed out an error. Hendrik Antoon Lorentz ( July 18, 1853 &ndash February 4, 1928) was a Dutch Physicist who shared the 1902 Nobel In addition to the two papers above [that is 52 and 53] Einstein and de Haas cowrote a "Comment" on paper 53 later in the year for the same journal. This topic was only indirectly related to Einstein's interest in physics, but, as he wrote to his friend Michele Besso, "In my old age I am developing a passion for experimentation. "

Calculations based on a model of electron spin as a circulating electric charge underestimate this magnetic moment by a factor of approximately 2, the Landé g-factor. In Physics, the Landé g-factor is a particular example of a G-factor, namely for an Electron with both spin and Orbital angular A correct description of this magnetic moment requires a treatment based on quantum electrodynamics. Quantum electrodynamics ( QED) is a relativistic Quantum field theory of Electrodynamics.

Note

  1. ^ Alice Calaprice, The Einstein Almanac (Johns Hopkins University Press, Baltimore, 2005), p. 45. ISBN 0-801-88021-1

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See also

External links

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