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4 Electricity and magnetism. 5 Heat. 6 Waves. 7 Gravity. 8 See also. 9 References. 10 Further reading. Toggle the table of contents.
Magnetism is the class of physical attributes that occur through a magnetic field, which allows objects to attract or repel each other. Because both electric currents and magnetic moments of elementary particles give rise to a magnetic field, magnetism is one of two aspects of electromagnetism .
The American Physical Society and the American Association of Physics Teachers recommend a full year of graduate study in electromagnetism for all physics graduate students. [4] A joint task force by those organizations in 2006 found that in 76 of the 80 US physics departments surveyed, a course using John Jackson 's Classical Electrodynamics ...
Cosmic age problem (1920s–1990s): The estimated age of the universe was around 3 to 8 billion years younger than estimates of the ages of the oldest stars in the Milky Way. Better estimates for the distances to the stars, and the recognition of the accelerating expansion of the universe, reconciled the age estimates.
Cover of A Treatise on Electricity and Magnetism. Electricity and magnetism were originally considered to be two separate forces. This view changed with the publication of James Clerk Maxwell's 1873 A Treatise on Electricity and Magnetism [6] in which the interactions of positive and negative charges were shown to be mediated by one force ...
Magnets exert forces and torques on each other through the interaction of their magnetic fields.The forces of attraction and repulsion are a result of these interactions. The magnetic field of each magnet is due to microscopic currents of electrically charged electrons orbiting nuclei and the intrinsic magnetism of fundamental particles (such as electrons) that make up the mater
Instead, magnetism in ordinary matter is due to two sources. First, electric currents create magnetic fields according to Ampère's law . Second, many elementary particles have an intrinsic magnetic moment , the most important of which is the electron magnetic dipole moment , which is related to its quantum-mechanical spin .
Rather than "magnetic charges", the basic entity for magnetism is the magnetic dipole. (If monopoles were ever found, the law would have to be modified, as elaborated below.) Gauss's law for magnetism can be written in two forms, a differential form and an integral form. These forms are equivalent due to the divergence theorem.