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 −5Ĭopper 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. 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.

State the relationship between resistivity and temperature.

State the relationship between resistance of a resistor and its length, cross-sectional area, and resistivity.

Describe the electrical component known as a resistor.

Differentiate between resistance and resistivity.

By the end of this section, you will be able to:

Interactive thermodynamics 3.2