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EXPRIMENT NO: 06 GENRAL PHYSICS COURSE NO. BSCS-307 RESISTANCE: The electrical resistance of an electrical element measures its opposition to the passage of an electric current ; the inverse quantity is electrical conductance, measuring how easily electricity flows along a certain path. Electrical resistance shares some conceptual parallels with the mechanical notion of friction . The SI unit of electrical resistance is the ohm (Ω), while electrical conductance is measured in Siemens (S). An object of uniform cross section has a resistance proportional to its resistivity and length and inversely proportional to its cross-sectional area. All materials show some resistance, except for superconductors , which have a resistance of zero. OHMS LAW: The resistance of an object is defined as the ratio of voltage across it to current through it: R=V/I For a wide variety of materials and conditions, the electrical resistance R is constant for a given temperature; it does not depend on the amount of current through or the potential difference (voltage) across the object. Such materials are called Omega materials. For objects made of omega materials the definition of the resistance, with R being a constant for that resistor, is known as Ohm's law
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DEFINITION OF 1 OHM: The ohm is defined as a resistance between two points of a conductor when a constant potential difference of 1 volt applied to these points, produces in the conductor a current of 1 ampere the conductor not being the seat of any electromotive force OMEGA=V/A=M^2.Kg/s.C^2=J/s.A^2=kg.m^2?s^3.A^2=J.s/C^2 In many cases the resistance of a conductor in ohms is approximately constant within a certain range of voltages, temperatures, and other parameters; one speaks of linear resistors. In other cases resistance varies (e.g., thermostats).
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This note was uploaded on 05/11/2011 for the course UBIT 411 taught by Professor Saleemelahi during the Spring '10 term at University of Karachi.

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