dipole
(ˈdaɪpəʊl)
[f. di-2 + pole n.2]
1. A pair of non-coincident equal and opposite electric charges or magnetic poles (usu. but not necessarily close together); an object, esp. a molecule, atomic particle, etc., having such charges or poles; dipole moment, the product of the distance between the two charges or poles of a dipole and the magnitude of either of them; the electric or magnetic moment of a dipole.
| 1912 Sci. Abstr. A. XV. 184 Taking the view that in dielectrics the electrons when displaced are urged back by forces proportional to those displacements, and that dipoles of constant electric moment are present also, the author [sc. Debye] obtains the following expression. 1931 W. M. Deans tr. Debye's Dipole Moment & Chem. Struct. 15 The methods in general use for the determination of dipole moments depend on the measurement of the dielectric constant of the substance in question. 1934 Nature 17 Mar. 415/2 The permanent dipole of a molecule in a solution may be regarded as surrounded by an ‘atmosphere’ of dipoles of opposite sign produced partly by induction in the polarisable solvent molecules and partly by orientation of adjacent permanent dipoles. Ibid. 26 May 802/1 Few branches of physical chemistry can show a more rapid development than the study of dipole moments. 1956 Sci. News XLI. 51 The electrical properties of organic materials are critically influenced by whether or not they contain permanent molecular dipoles. 1957 Endeavour XVI. 188/1 Nuclei with spin quantum numbers greater than one-half usually possess an electric quadrupole moment as well as a magnetic dipole moment. 1965 A. Holmes Princ. Physical Geol. (ed. 2) xxvii. 989 The main part of the magnetic field is..like that of a powerful bar magnet (a ‘dipole’) placed near the middle of the earth. 1968 R. A. Lyttleton Myst. Solar Syst. iii. 97 The dipole-moment [of Mars] can be at most 1/3000th that of the Earth. |
2. Radio. An aerial consisting either of two equal metal rods mounted close together in line or of a single rod, with the electrical connection made to the centre of the aerial and with a total length usually about half the wavelength to be transmitted or received; freq. attrib. (See also quots. 1947, 1960.)
| 1929 Proc. Inst. Radio Engin. Dec. 2207 (caption) Position of the dipole on the airplane... Securely stretched dipoles are most commonly used... Fig. 15 shows the installation of such a dipole antenna. 1930 Telegr. & Teleph. Jrnl. XVII. 31/1 These arrays generally consist of a number of dipoles..arranged in the form of a curtain. 1931 Jrnl. R. Aeronaut. Soc. XXXV. 761 The directional properties were investigated with a di-pole receiver. 1943 Electronic Engin. XVI. 197 Dipoles of length other than half wavelength. 1947 Siegert & Purcell in L. N. Ridenour Radar System Engin. iii. 82 ‘Window’ is the British and most commonly used code name for conducting foil or sheet cut into pieces of such a size that each piece resonates as a dipole at enemy radar frequency. 1955 Sci. Amer. Mar. 38/1 A parabolic ‘dish’, either solid or made of a wire screen, reflects incoming radio waves to a focal point, where a small dipole or rod picks up the energy and converts it into an electric current which is then conveyed by a cable to a sensitive receiver. 1960 Times 16 Sept. 6/7 The idea of using a cloud of thin strips of metal foil to reflect radio waves originated during the war... Such a strip is tuned automatically to a wavelength twice the length of the strip—an aerial or reflector of this kind being known as a dipole. 1964 Ann. Reg. 1963 185 On 9 May..the U.S. released..some 400 million copper dipoles, or space needles, each about 3/4 inch long. |