Chapter 25 current, resistance and electromotive force. Lecture 8 physics 272 electric currents resistance. Electric resistivity is defined as the ratio of electric field intensity at any point in the conductor and the current density at that point i. You already know that not everything conducts electricity equally well, and that some materials like copper resist very little, while others like rubber provide enough resistance to effectively prevent the.
The electrical resistance of a wire would be expected to be greater for a longer wire, less for a wire of larger cross sectional area, and would be expected to depend upon the material out of which the wire is made. A heating element is a wire with crosssectional area of 2. We say the battery applies an electromotive force, or emf for short. Chapter 25 current, resistance and electromotive force current resistivity resistance electromotive force and circuits energy and power in electric circuits theory of metallic conduction. The resistance of all substances changes to some degree with temperature. The resistance r of a uniform cylinder of length l, of crosssectional area a. Electric current, current density, resistivity and resistance. In this small ebook we will learn all we need to know about current electricity but in short and then well have some. Resistance definition is an act or instance of resisting. The same may be said of a solar cell, or a generator. In the case of pure metals, the resistance increases rapidly with a rise in temperature. An introduction to electrical resistivity in geophysics. The resistance r of a conductor is the ratio of the potential difference.
Resistivity is the tendency of a material to behave as a resistor. Consider free electron motion without any external electric field. Electric current, resistance and resistivity physicscatalyst. Pdf electrical conductivity and resistivity researchgate. You already know that not everything conducts electricity equally well, and that. A battery causes electric current to flow through a circuit. Electron moves from p1 p2 consider electron motion with an external electric field. An unusually low resistance might indicate that two contacts. The measured soil resistivity values were then used to evaluate the ground resistance values of a grounding grid with rod for the wet soil site and without rods for the dry soil site. In this equation, r is the resistance of the object in question, is the resistivity of the material the object is made of, is the length of the material, and a is the crosssectional area the current ows through.
Resistance and resistivity electric resistance is measured in ohms. Pdf soil resistivity and ground resistance for dry and. Resistivity and resistance mercer university physics. Pdf resistance and resistivity muhammad habibie academia. Scribd is the worlds largest social reading and publishing site. Experimentally, the dependence upon these properties is a straightforward one for a wide range. Resistance definition of resistance by merriamwebster. Various factors affect the resistance of a material.
752 403 595 356 280 256 995 520 478 873 1143 1390 1340 1113 1352 453 591 564 1352 577 677 1414 749 1217 1444 3 1364 225 685 1224