Electromagnetic momentum density and the Poynting vector in static fields
作者:
Francis S. Johnson,
Bruce L. Cragin,
R. Richard Hodges,
期刊:
American Journal of Physics
(AIP Available online 1994)
卷期:
Volume 62,
issue 1
页码: 33-41
ISSN:0002-9505
年代: 1994
DOI:10.1119/1.17738
出版商: American Association of Physics Teachers
关键词: MOMENTUM DENSITY;ELECTROMAGNETIC FIELDS;MAGNETIC DIPOLES;SOLENOIDS;ELECTRIC CHARGES;ANGULAR MOMENTUM;ELECTRIC FIELDS;MAGNETIC FIELDS;CAPACITORS;POLARIZATION
数据来源: AIP
摘要:
Many static configurations involving electrical currents and charges possess angular momentum in electromagnetic form; two examples are discussed here, an electric charge in the field of a magnetic dipole, and an electric charge in the vicinity of a long solenoid. These provide clear evidence of the physical significance of the circulating energy flux indicated by the Poynting vector, as the angular momentum of the circulating electromagnetic energy can be converted to mechanical angular momentum by turning off the magnetic field. Electromagnetic momentum is created whenever electric fields change in the presence of a magnetic field and whenever magnetic fields change in the presence of an electric field. When simple dielectrics are involved, the momentum density can be resolved into two components, a pure‐field component ε0E×Band a component χeε0E×Bassociated with the polarization of the dielectric, the sum being εrε0E×B=D×B. It is argued that the latter component should be considered to be part of the electromagnetic momentum density, whose value then isD×B.
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