| 释义 |
Nernst|nɛːrnst, nɜːnst|
[Name of Walther Hermann Nernst (1864–1941), German physical chemist.]
a. Used attrib. to designate an electric incandescent lamp invented by Nernst in which an unenclosed rod or wire consisting of a mixture of rare earths and other metallic oxides (as magnesia or zirconia) is made hot and luminous by the passage of an electric current (after being first brought to a conducting state by heating), and which is used esp. as a source of infra-red radiation.
1899Chambers's Jrnl. 25 Mar. 269/2 For some time there have been rumours of an electric lamp on an entirely new principle, and..the contrivance was recently exhibited at the Society of Arts, London. It is known as the Nernst incandescent electric lamp, and its chief peculiarity is that it employs a rod of refractory earth in place of the usual carbon filament, and that this material is not enclosed in a glass exhausted of air. 1912W. S. Franklin Electric Lighting v. 134 There are five important kinds of glow lamps as follows:{ddd} (e) The Nernst lamp in which the glower is a small rod of porcelain-like material. 1950L. J. Brady in M. G. Mellon Analytical Absorption Spectrosc. viii. 444 One serious objection to the Nernst glower is the frequent mechanical failure of the source due to the poor bonding of the platinum leads to the element itself. 1962R. E. Dodd Chem. Spectrosc. i. 16 For use in the infra-red region, mainly beyond 2µ, the hot body takes the form of a rod of semi-conducting lanthanon oxides, a Nernst glower. Ibid. 17 The Nernst filament is only suitable for the near infra-red and visible.
b. Used attrib. with reference to a thermo-magnetic effect investigated by Nernst, in which a temperature gradient in a metal subject to a magnetic field at right angles to the gradient gives rise to an e.m.f. in a direction at right angles to both.
1901M. G. Lloyd in Amer. Jrnl. Sci. CLXII. 57 It has already been proposed† to call the galvano-magnetic temperature-difference, the thermo-magnetic temperature-difference, and the thermo-magnetic potential-difference by the respective names, Ettingshausen effect, Leduc effect and Nernst effect. [Note] † Thesis: The Transversal Thermo-magnetic Effect in Bismuth, M. G. Lloyd, Philadelphia, 1900; Beiblätter, 24, p. 1014. 1911Physical Rev. XXXIII. 300 Both the Hall electromotive force and the Nernst electromotive force seem to be proportional to the intensity of magnetization in the plate rather than to the magnetic field. 1960E. H. Putley Hall Effect & Related Phenomena ii. 27 In the Nernst effect, electrons attempting to diffuse down a temperature gradient are deflected by a magnetic field but a transverse electric field is set up to balance out the Lorentz force. Ibid. 28 The units for the Nernst coefficient are cm2 sec-1 (°K)-1 or m2 sec-1 (°K)-1.
c. Used attrib. and in the possessive to designate a theorem in thermodynamics enunciated by Nernst: the change in entropy accompanying a chemical reaction between pure crystalline solids tends to zero as the temperature at which it occurs tends to absolute zero. (Also called the third law of thermodynamics, esp. in more generalized formulations.)
1913J. R. Partington Text-bk. Thermodynamics xvii. 484 The required information is furnished by a hypothesis put forward in 1906 by W. Nernst, and usually called by German writers ‘das Nernstsche Wärmetheorem’. We can refer to it without ambiguity as Nernst's Theorem. 1928J. K. Roberts Heat & Thermodynamics xviii. 354 Such a wide range of reactions is considered that we are certainly justified in regarding the Nernst Heat Theorem as being established as a first approximation. Ibid. 355 If the Nernst Theorem as originally stated should prove to be only a first approximation, the theorem does not on that account become less important. 1971G. Socrates Thermodynamics & Statistical Mech. vii. 139 An alternative statement of Nernst's heat theorem is: It is impossible to reduce the temperature of any system to absolute zero in a finite number of operations. |