Copper and aluminum are among the least expensive materials with suitable conducting ability to permit their use in wires of household circuits. The conducting ability of a material is often indicated by its resistivity. The resistivity of a material is dependent upon the material's electronic structure and its temperature. For most but not all materials, resistivity increases with increasing temperature. The table below lists resistivity values for various materials at temperatures of 20 degrees Celsius.

As seen in the table, there is a broad range of resistivity values for various materials. Those materials with lower resistivities offer less resistance to the flow of charge; they are better conductors. The materials shown in the last four rows of the above table have such high resistivity that they would not even be considered to be conductors.

Resistance is a numerical quantity that can be measured and expressed mathematically. The standard metric unit for resistance is the ohm, represented by the Greek letter omega -. The equation representing the dependency of the resistance R of a cylindrically shaped conductor e. Consistent with the discussion above, this equation shows that the resistance of a wire is directly proportional to the length of the wire and inversely proportional to the cross-sectional area of the wire.

As shown by the equation, knowing the length, cross-sectional area and the material that a wire is made of and thus, its resistivity allows one to determine the resistance of the wire.

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Resistors are one of the more common components in electrical circuits. Most resistors have stripes or bands of colors painted on them.

## Resisting Current

The colors reveal information about the resistance value. Perhaps you're doing a lab and need to know the resistance of a resistor used in the lab.

Use the widget below to determine the resistance value from the colored stripes. Household circuits are often wired with two different widths of wires: gauge and gauge. Thus, gauge wire has a wider cross section than gauge wire. A Amp circuit used for wall receptacles should be wired using gauge wire and a Amp circuit used for lighting and fan circuits should be wired using gauge wire. Explain the physics behind such an electrical code.

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• A gauge wire is wider than gauge wire and thus has less resistance. The lesser resistance of gauge wire means that it can allow charge to flow through it at a greater rate - that is, allow a larger current. Thus, gauge wire is used in circuits which are protected by Amp fuses and circuit breakers.

On the other hand, the thinner gauge wire can support less current owing to its larger resistance; it is used in circuits which are protected by Amp fuses and circuit breakers. Based on the information stated in the above question, explain the risk involved in using gauge wire in a circuit that will be used to power an ampere power saw. Thus, gauge wire can safely support a circuit that uses an appliance drawing up to 20 Amps of current.

In fact, a Amp circuit is protected by a fuse or circuit breaker that will flip off when the current reaches 20 Amps. If a gauge wire was used on the same circuit, then the breaker would allow up to 20 Amps to flow through it.

## Resistance

It could overheat and thus lead to the risk of fire. A Amp circuit should never be wired using gauge wire. Determine the resistance of a 1-mile length of gauge copper wire. Two wires - A and B - with circular cross-sections have identical lengths and are made of the same material. Yet, wire A has four times the resistance of wire B. Communication between units is usually by encrypted communications.

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