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In electromagnetism, current density is the amount of charge per unit time that flows through a unit area of a chosen cross section. [1] The current density vector is defined as a vector whose magnitude is the electric current per cross-sectional area at a given point in space, its direction being that of the motion of the positive charges at this point.
Regardless of the driving force, the current density is found to be greatest at the conductor's surface, with a reduced magnitude deeper in the conductor. That decline in current density is known as the skin effect and the skin depth is a measure of the depth at which the current density falls to 1/e of its value near the surface. Over 98% of ...
The maximum possible current density of copper in open air is approximately 3.1 × 10 6 A/m 2, above which it begins to heat excessively. [17] Copper is one of a few metallic elements with a natural color other than gray or silver. [18] Pure copper is orange-red and acquires a reddish tarnish when exposed to air.
The typical current density at which electromigration occurs in Cu or Al interconnects is 10 6 to 10 7 A/cm 2. For solder joints (SnPb or SnAgCu lead-free) used in IC chips, however, electromigration occurs at much lower current densities, e.g. 10 4 A/cm 2. It causes a net atom transport along the direction of electron flow.
Silver, although it is the least resistive metal known, has a high density and performs similarly to copper by this measure, but is much more expensive. Calcium and the alkali metals have the best resistivity-density products, but are rarely used for conductors due to their high reactivity with water and oxygen (and lack of physical strength).
Charge carrier density, also known as carrier concentration, denotes the number of charge carriers per volume. In SI units, it is measured in m −3. As with any density, in principle it can depend on position. However, usually carrier concentration is given as a single number, and represents the average carrier density over the whole material.
New York: The International Nickel Company, Inc., 1941: 16. — "Values ranging from 21.3 to 21.5 gm/cm 3 at 20 °C have been reported for the density of annealed platinum; the best value being about 21.45 gm/cm 3 at 20 °C." 21.46 g/cm 3 — Rose, T. Kirke. The Precious Metals, Comprising Gold, Silver and Platinum. New York: D. Van Nostrand ...
Copper Thermite (Al + CuO as oxidizer) [citation needed] 4.13: 20.9: Thermite (powder Al + Fe 2 O 3 as oxidizer) 4.00: 18.4: Hydrogen peroxide decomposition (as monopropellant) 2.7: 3.8: battery, Lithium-ion nanowire: 2.54: 95% [clarification needed] [13] battery, Lithium Thionyl Chloride (LiSOCl2) [14] 2.5: Water 220.64 bar, 373.8 °C ...