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An electromagnet is a type of magnet in which the magnetic field is produced by an electric current. Electromagnets usually consist of wire (likely copper) wound into a coil. A current through the wire creates a magnetic field which is concentrated along the center of the coil. The magnetic field disappears when the current is turned off.
Symbol [1] Name of quantity Unit name Symbol Base units E energy: joule: J = C⋅V = W⋅s kg⋅m 2 ⋅s −2: Q electric charge: coulomb: C A⋅s I electric current: ampere
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The factual setup of the experiment is not completely clear, nor if current flowed across the needle or not. An account of the discovery was published in 1802 in an Italian newspaper, but it was largely overlooked by the contemporary scientific community, because Romagnosi seemingly did not belong to this community.
Continuous charge distribution. The volume charge density ρ is the amount of charge per unit volume (cube), surface charge density σ is amount per unit surface area (circle) with outward unit normal nĚ‚, d is the dipole moment between two point charges, the volume density of these is the polarization density P.
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Field coil electromagnet on the stator of an AC universal motor. Canon AF-10 Date old camera shutter driver coil. Electromagnets are coils that generate a magnetic field for some external use, often to exert a mechanical force on something. [15] or remove existing background fields. [16] A few specific types:
In case of stator windings that are electrically commutated or supplied by an m-phase net, these phase windings are often banked (distributed windings). The number of holes q constitutes a characteristic dimension of the winding setup. It states how many slots q per phase m and pole (provided by pole number 2p) are available. [citation needed]