Where ρ ρ is the resistivity of the material at temperature T, α α is the temperature coefficient of the material, and ρ 0 ρ 0 is the resistivity at T 0 T 0, usually taken as T 0 = 20.00 ° C T 0 = 20.00 ° C. In many materials, the dependence is approximately linear and can be modeled using a linear equation: In other materials, such as carbon, the resistivity decreases with increasing temperature. The increasing temperature causes increased vibrations of the atoms in the lattice structure of the metals, which impede the motion of the electrons. In fact, in most conducting metals, the resistivity increases with increasing temperature. In some materials, such as copper, the resistivity increases with increasing temperature. Looking back at Table 9.1, you will see a column labeled “Temperature Coefficient.” The resistivity of some materials has a strong temperature dependence. What other materials are used for wiring and what are the advantages and disadvantages? Temperature Dependence of Resistivity Summarizing, for a conductor to be a suitable candidate for making wire, there are at least three important characteristics: low resistivity, high tensile strength, and high ductility. Ductility is a measure of a material’s ability to be drawn into wires and a measure of the flexibility of the material, and copper has a high ductility. A third important characteristic is ductility. Copper has a high tensile strength, 2 × 10 8 N m 2 2 × 10 8 N m 2. The tensile strength of a material is the maximum amount of tensile stress it can take before breaking. Also important is the tensile strength, where the tensile strength is a measure of the force required to pull an object to the point where it breaks. Copper has the highest electrical conductivity rating, and therefore the lowest resistivity rating, of all nonprecious metals. ( 3.5 − 60 ) × 10 −5 ( 3.5 − 60 ) × 10 −5Ĭheck Your Understanding Copper wires are routinely used for extension cords and house wiring for several reasons. In these cases, the current density can be modeled as In some materials, including metals at a given temperature, the current density is approximately proportional to the electrical field. The current density J → J → that results depends on the electrical field and the properties of the material. When a voltage is applied to a conductor, an electrical field E → E → is created, and charges in the conductor feel a force due to the electrical field. This resistivity is crudely analogous to the friction between two materials that resists motion. The material can resist the flow of the charges, and the measure of how much a material resists the flow of charges is known as the resistivity. The amount of current depends not only on the magnitude of the voltage, but also on the characteristics of the material that the current is flowing through. Resistance physics calculator free#The electrical field, in turn, exerts force on free charges, causing current. When a voltage source is connected to a conductor, it applies a potential difference V that creates an electrical field. All such devices create a potential difference and are referred to as voltage sources. What drives current? We can think of various devices-such as batteries, generators, wall outlets, and so on-that are necessary to maintain a current.
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