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The gauss is the unit of magnetic flux density B in the system of Gaussian units and is equal to Mx/cm 2 or g/Bi/s 2, while the oersted is the unit of H-field. One tesla (T) corresponds to 10 4 gauss, and one ampere (A) per metre corresponds to 4π × 10 −3 oersted.
10 −1 T: decitesla: 100 mT: 1 kG: Penny-sized neodymium magnet: 150 mT: 1.5 kG: Sunspot: 10 0 T tesla 1 T: 10 kG: Inside the core of a 60 Hz power transformer (1 T to 2 T as of 2001) [10] [11] or voice coil gap of a loudspeaker magnet (1 T to 2.4 T as of 2006) [12] 1.5 T to 7 T: 15 kG to 70 kG
The tesla (symbol: T) is the unit of magnetic flux density (also called magnetic B-field strength) in the International System of Units (SI). One tesla is equal to one weber per square metre .
One difference between the Gaussian and SI systems is in the factor 4π in various formulas that relate the quantities that they define. With SI electromagnetic units, called rationalized, [3] [4] Maxwell's equations have no explicit factors of 4π in the formulae, whereas the inverse-square force laws – Coulomb's law and the Biot–Savart law – do have a factor of 4π attached to the r 2.
In electromagnetism, Jefimenko's equations (named after Oleg D. Jefimenko) give the electric field and magnetic field due to a distribution of electric charges and electric current in space, that takes into account the propagation delay (retarded time) of the fields due to the finite speed of light and relativistic effects.
where n is the number of charges, q i is the amount of charge associated with the ith charge, r i is the position of the ith charge, r is the position where the electric field is being determined, and ε 0 is the electric constant. If the field is instead produced by a continuous distribution of charge, the summation becomes an integral:
The magnetic field (marked B, indicated by red field lines) around wire carrying an electric current (marked I) Compass and wire apparatus showing Ørsted's experiment (video [1]) In electromagnetism , Ørsted's law , also spelled Oersted's law , is the physical law stating that an electric current induces a magnetic field .
In classical electromagnetism, magnetic vector potential (often called A) is the vector quantity defined so that its curl is equal to the magnetic field: =.Together with the electric potential φ, the magnetic vector potential can be used to specify the electric field E as well.