Electrical resistance - Wikipedia, the free encyclopedia

# Electrical resistance - Wikipedia, the free encyclopedia -...

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Electromagnetism Electricity · Magnetism Electrostatics Electric charge · Coulomb's law · Electric field · Electric flux · Gauss's law · Electric potential · Electrostatic induction · Electric dipole moment · Polarization density Magnetostatics Ampère’s law · Electric current · Magnetic field · Magnetization · Magnetic flux · Biot–Savart law · Magnetic dipole moment · Gauss's law for magnetism Electrodynamics Free space · Lorentz force law · emf · Electromagnetic induction · Faraday’s law · Lenz's law · Displacement current · Maxwell's equations · EM field · Electromagnetic radiation · Liénard-Wiechert Potential · Maxwell tensor · Eddy current Electrical Network Electrical conduction · Electrical resistance · Capacitance · Inductance · Impedance · Resonant cavities · Waveguides Covariant formulation Electromagnetic tensor · EM Stress-energy tensor · Four-current · Electromagnetic four-potential Scientists Electrical resistance From Wikipedia, the free encyclopedia The electrical resistance of an object is a measure of its opposition to the passage of a steady electric current. An object of uniform cross section will have a resistance proportional to its length and inversely proportional to its cross-sectional area, and proportional to the resistivity of the material. Discovered by Georg Ohm in the late 1820s, [1] electrical resistance shares some conceptual parallels with the mechanical notion of friction. The SI unit of electrical resistance is the ohm, symbol . Resistance's reciprocal quantity is electrical conductance measured in siemens, symbol S. The resistance of a resistive object determines the amount of current through the object for a given potential difference across the object, in accordance with Ohm's law: where R is the resistance of the object, measured in ohms, equivalent to J·s/C 2 V is the potential difference across the object, measured in volts I is the current through the object, measured in amperes For a wide variety of materials and conditions, the electrical resistance does not depend on the amount of current through or the amount of voltage across the object, meaning that the resistance R is constant for the given temperature and material. Therefore, the resistance of an object can be defined as the ratio of voltage to current: In the case of nonlinear objects (not purely resistive, or not 11/10/2009 Electrical resistance - Wikipedia, the fre… en.wikipedia.org/…/Electrical_resistance 1/7

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Ampère · Coulomb · Faraday · Gauss · Heaviside · Henry · Hertz · Lorentz · Maxwell · Tesla · Weber · Ørsted A 750-k resistor, as identified by its electronic color code. An ohmmeter could be used to verify this value. obeying Ohm's law), this ratio can change as current or
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