Wiktor Wise
Copper is a widely used electrical conductor due to its low electrical resistance. It has the second lowest electrical resistivity, behind silver, which is much more expensive. The low electrical resistance of copper means it readily allows the movement of electric charge, making it ideal for use in household electrical wires, electrical machinery, generators, and outdoor power lines. The electrical resistance of copper decreases with decreasing temperature and increasing pressure. At very low temperatures, copper becomes a superconductor with zero resistance.
| Characteristics | Values |
|---|---|
| Electrical Resistance | Dependent on geometric properties of a material |
| Resistivity | Low |
| Conductivity | High |
| Temperature Coefficient of Resistance | 0.393% per degree Celsius |
| Resistivity at 0°C | 0.00427 |
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What You'll Learn
Copper has the highest electrical conductivity rating of all non-precious metals
Copper is a material with high electrical conductivity, meaning it can transport electric charge effectively. This property is essential in electrical wiring systems. Copper has the highest electrical conductivity rating of all non-precious metals, with an electrical resistivity of 16.78 nΩ•m at 20 °C.
The high electrical conductivity of copper is explained by the theory of metals in their solid state. In a copper atom, the outermost 4s energy zone, or conduction band, is only half-filled, allowing many electrons to carry the electric current. When a voltage source is connected to a copper conductor, it creates an electrical field that exerts a force on these free electrons, causing them to accelerate and generate an electric current.
The resistance encountered by these electrons as they travel through the material contributes to its overall electrical resistivity. In the case of copper, the average distance travelled by electrons between collisions with impurity atoms, vacancies, lattice ions, and imperfections is defined as the mean free path, which is inversely proportional to the resistivity of the metal. This means that the longer the mean free path, the lower the resistivity. Copper's high conductivity and low resistivity make it a preferred choice for electrical wiring and other applications.
While silver, a precious metal, has a slightly higher electrical conductivity than copper, it is much more expensive and has lower tensile strength. This limits silver's use to special applications. Other materials used for wiring, such as aluminium, gold, and calcium, have their own advantages and disadvantages. For example, aluminium is cheaper than copper but has higher resistivity and lower ductility and tensile strength. Calcium has excellent resistivity-density products but is rarely used due to its high reactivity with water and oxygen.
In summary, copper's combination of high electrical conductivity, good tensile strength, and resistance to corrosion makes it a versatile and cost-effective choice for electrical conductors in various applications, including building wire, motor windings, electrical cables, and telecommunications.
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Resistivity and wire length
The electrical resistance of copper is approximately 1.7 x 10^-8 Ω m (0.0174 μΩ m). Copper is a material with low resistivity ρ and high conductivity σ. This means that even a small electric field can pull a lot of current through it.
Resistivity is an intrinsic property of a material, indicating how much it resists the flow of electric current. It is measured in ohm-meters (Ω·m). The longer the wire, the higher the resistance. This is because a longer wire provides more material for electrons to travel through, encountering more resistance along the way.
The relationship between a wire's length and its resistance is governed by the formula R=ρAL, where R is resistance, ρ (rho) is the material's resistivity, L is the length of the wire, and A is its cross-sectional area. The resistance of a wire is directly proportional to its length and inversely proportional to its cross-sectional area. This means that a long, thin copper wire has a much larger resistance than a thick, short copper wire.
The length of a wire is a significant factor in determining its resistance, and this holds true for a variety of metals, including copper. Understanding how wire length affects resistance is crucial in applications such as heating elements and electrical circuits.
The electrons carrying the current in a longer wire have to travel a greater distance, undergoing more frequent collisions with the atoms and ions of the conductor material. Each collision impedes the flow of electrons, resulting in higher overall resistance. Therefore, while the current remains constant in a longer wire, more power (larger potential difference) is required to maintain this current.
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Impurities and defects
Impurities in copper, such as other metals or foreign atoms, disrupt the regular lattice or crystal structure of copper. This disruption creates scattering centres that impede the flow of electrons, leading to increased resistance. Elements such as phosphorus, sulfur, iron, and oxygen can have this effect, with oxygen forming copper oxide, which has higher resistivity than pure copper. The presence of impurities increases electron collisions, further contributing to higher resistance.
Defects in the crystal structure of copper, including grain boundaries, dislocations, and vacancies, also play a significant role in resistance. These defects obstruct the orderly movement of electrons, causing more scattering and resistance. Cold working, a process that involves deforming copper at room temperature, introduces these defects and slightly increases resistance. On the other hand, annealing, a heat treatment process, can reduce resistance by relieving internal stresses and promoting a more uniform crystal structure.
The interplay between temperature and impurities is crucial in understanding resistance. While higher temperatures generally increase resistance due to enhanced atomic vibrations, at very low temperatures, the effects of impurities and defects become more prominent, resulting in a residual resistance that persists even at absolute zero. This phenomenon is essential to consider in applications requiring high precision and low temperatures, such as cryogenic systems.
Overall, understanding and managing impurities and defects in copper are vital for optimising its performance in electrical applications. By controlling the purity and processing conditions, engineers can minimise resistance and enhance copper's efficiency as a conductor, ensuring its reliability in modern electrical infrastructure.
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Copper's high ductility and tensile strength
Copper is a metal with unique properties that make it suitable for a wide range of applications. One of its key characteristics is its high ductility, which is the ability of a material to deform plastically under load without failing or fracturing. This is in contrast to brittle materials like glass, which break without noticeable deformation. Copper's ductility allows it to be shaped and formed without cracking or breaking, making it highly malleable and useful for a variety of manufacturing processes.
In addition to its high ductility, copper also exhibits comparatively high tensile strength. Tensile strength refers to the maximum stress a material can withstand during deformation. Copper alloys, in particular, become stronger and more ductile as temperatures decrease. Tests on various copper alloys, including brasses and bronzes, have shown that they retain excellent impact resistance down to extremely low temperatures. This combination of high ductility and tensile strength gives copper and its alloys the ability to withstand significant stress and deformation without failing, making them ideal for structural applications.
The relationship between ductility and strength in copper alloys is complex. While larger deformations can increase the strength of the alloy, they simultaneously reduce its ductility, presenting a trade-off between the two properties. The grain size within the alloy also plays a role in this relationship; alloys with smaller grain sizes tend to have higher strength due to an increased ratio of grain boundaries. Through specific processing techniques, such as heat treatment or seeding of the melt, the grain size can be reduced, resulting in stronger copper alloys with improved tensile strength.
The high ductility and tensile strength of copper are not its only desirable attributes. Copper is also known for its excellent electrical conductivity, which is closely related to its low electrical resistance or resistivity. Resistivity describes how difficult it is for electrical current to flow through a material, and copper's low resistivity means it readily conducts electricity with minimal resistance. This property, coupled with its ductility and strength, makes copper an excellent choice for electrical wiring and other applications where efficient conduction is required. Overall, copper's unique combination of high ductility, tensile strength, and electrical conductivity contributes to its versatility and widespread use in a variety of industries.
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Silver is the only metal with higher electrical conductivity than copper
Copper is a metal with high electrical conductivity, which is a measure of how well a material transports an electric charge. It is used extensively in electrical wiring systems due to its superior conductivity. In fact, copper has the highest electrical conductivity rating of all non-precious metals, with an electrical resistivity of 16.78 nΩ•m at 20 °C. This property is due to the structure of the copper atom, where the outermost 4s energy zone is only half-filled, allowing many electrons to carry the electric current.
However, silver is the only metal that surpasses copper in electrical conductivity. Silver, a precious metal, has an electrical conductivity of 106% of annealed copper on the IACS scale and an electrical resistivity of 15.9 nΩ•m at 20 °C. This makes silver the least resistive metal known. Despite silver's superior conductivity, it is not as widely used as copper in electrical applications due to its high cost and low tensile strength.
The high ductility of copper, which is only surpassed by gold and silver, makes it ideal for wiring systems. Copper can be bent, twisted, and pulled without stretching or breaking, ensuring the safety and integrity of electrical connections. Additionally, copper exhibits excellent creep characteristics, minimising loosening at connections and reducing the risk of dangerous arcing and overheating.
Another advantage of copper is its resistance to corrosion. It resists corrosion from moisture, humidity, industrial pollution, and other atmospheric influences. While corrosion oxides, chlorides, and sulfides can form on copper, they are conductive and do not significantly impact its electrical properties. Copper's high strength and low coefficient of thermal expansion further contribute to its suitability for electrical applications.
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Frequently asked questions
Electrical resistance describes how difficult it is to make an electric current flow through a material.
Copper has a higher electrical conductivity rating than all non-precious metals, meaning it has a lower electrical resistance. The electrical resistivity of copper = 16.78 nΩ•m at 20 °C.
The resistance of a copper wire is dependent on its length and its cross-sectional area. A long, thin copper wire has a much larger resistance than a thick, short copper wire.
The electrical resistivity of a metallic conductor such as copper decreases as the temperature lowers.
