Umair Gaines
Electrical resistivity is a fundamental property of a material that measures its electrical resistance or how strongly it resists electric current. Resistivity is commonly represented by the Greek letter rho (ρ). The SI unit of electrical resistivity is the ohm-meter (Ω⋅m). A low resistivity indicates a material that readily allows electric current. On the other hand, electrical conductivity, the inverse of resistivity, measures a material's ability to conduct an electric current. The goal of material researchers is to find a thermoelectric material with the highest possible electrical conductivity.
| Characteristics | Values |
|---|---|
| Definition | Electrical resistivity is a fundamental property of a material that measures its electrical resistance or how strongly it resists electric current. |
| Symbol | Commonly represented by the Greek letter ρ (rho) |
| Unit | Ohm-metre (Ω⋅m) |
| Relation to Conductivity | Electrical conductivity is the reciprocal of electrical resistivity. |
| Relation to Resistance | Electrical resistance is not the same as resistivity. While resistivity is a material property, resistance is the property of an object. |
| Temperature Dependence | The value of resistivity depends on the temperature of the material. Resistivity of metallic conductors generally increases with a rise in temperature, while resistivity of semiconductors generally decreases with a temperature rise. |
| Material Comparison | Every material has its own characteristic resistivity. For example, rubber has a far larger resistivity than copper. |
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What You'll Learn
Resistivity vs. resistance
Electrical resistivity is a fundamental property of a material that measures its electrical resistance or how strongly it impedes electric current. It is commonly represented by the Greek letter rho (ρ) and has SI units of ohm-metres (Ω⋅m). Resistivity is an intrinsic property of a material and does not depend on its geometric properties. For example, all pure copper (Cu) wires, irrespective of their shape and size, have the same resistivity.
Electrical resistance, on the other hand, is the property of an object. It is expressed in ohms and is determined by the combination of the shape and the resistivity of the material. For instance, a long, thin copper wire has a much larger resistance than a thick, short copper wire. The resistance value of a wire depends on three parameters: resistivity, length, and diameter.
Resistivity and conductivity are intensive properties of materials, signifying the opposition of a standard cube of material to current. Electrical resistance and conductance, on the other hand, are extensive properties that indicate the opposition of a specific object to electric current. Conductivity is the inverse of resistivity and is a measure of how well a material conducts electric current. It is commonly expressed in siemens per metre (S/m).
The resistivity of a material is dependent on temperature and is usually given for room temperature (20°C). The resistivity of metallic conductors generally increases with a rise in temperature, while the resistivity of semiconductors, such as carbon and silicon, decreases with an increase in temperature. The change in resistivity due to temperature change is described by the temperature coefficient.
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Resistivity and temperature
The resistivity of a material is dependent on its temperature. Resistivity is the property of a material that measures its electrical resistance or how strongly it resists electric current. It is commonly represented by the Greek letter rho (ρ).
The resistivity of metallic conductors generally increases with a rise in temperature. This is because, at higher temperatures, the atoms vibrate more rapidly and over larger distances, causing the electrons moving through a metal to make more collisions, effectively making the resistivity higher. Conversely, the resistivity of semiconductors, such as carbon and silicon, generally decreases with a temperature rise. This is because, as the temperature increases, more electrons are shaken free from their valence duties, and they then take on the task of conducting electricity. Thus, the conductivity of a semiconductor increases with increasing temperature.
The temperature coefficient of resistance, α, of a metal (or other substance) is the fractional increase in its resistivity per unit rise in temperature. In SI units, it is expressed in K-1. The temperature coefficient of resistance is used to calculate the change of resistance with temperature. Thermistors, for example, make use of this property to measure temperature. Platinum resistance thermometers also use the resistivity of platinum as a function of temperature to measure temperature in conditions where other thermometers may not be useful.
The resistance of an object depends on its shape and the material of which it is composed. For a cylinder, the resistance R is directly proportional to its length L, and inversely proportional to its cross-sectional area A. If L and A do not change greatly with temperature, R will have the same temperature dependence as ρ.
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Resistivity of ceramics
Electrical resistivity is a property of a material that measures its resistance to electric current. It is denoted by the Greek letter rho (ρ) and measured in ohm-meters (Ω⋅m). Resistivity is an intrinsic property of a material and is independent of its geometric characteristics. Materials with high resistivity are poor conductors of electricity, while those with low resistivity are good conductors.
Ceramics are generally excellent electrical insulators, meaning they effectively resist the transmission of electric currents. They are often used in electronics, defence, medical instrumentation, energy, transport, aeronautics, and spatial applications. However, ceramics can be modified to improve their ability to transmit electric currents, thereby reducing their resistivity. For instance, dopants can be added to ceramics to enhance their current-carrying capacity.
The resistivity of ceramic materials varies. For example, Shapal Hi-M Soft, a hybrid type of machinable aluminium nitride ceramic, has a resistivity of 1 x 10^15 Ohm-cm. In contrast, Silicon Nitride, an advanced ceramic material, has a lower resistivity of 1 x 10^14 Ohm-cm. Silicon carbide is the least insulating ceramic, with a resistivity of around 1 x 10^6 Ohm-cm or less for certain forms.
The resistivity of ceramics can be further tailored for specific applications. For instance, in semiconductor chip fabrication, electrostatic chucks require a customised ceramic with a narrow target range of volume resistivity, typically between 10^6 to 10^8 Ohm-m at the wafer processing temperature. Alumina or aluminium nitride ceramics are often used for this purpose.
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Resistivity and conductivity
Electrical resistivity is a fundamental property of a material that measures its electrical resistance or how strongly it resists electric current. Resistivity is commonly represented by the Greek letter ρ (rho). The SI unit of electrical resistivity is the ohm-metre (Ω⋅m). A low resistivity indicates a material that readily allows the flow of electric current.
Every material has its own characteristic resistivity. For example, rubber has a far larger resistivity than copper. The resistivity of a material is dependent on the temperature and is usually given for room temperature (20°C). Resistivity of metallic conductors generally increases with a rise in temperature, while the resistivity of semiconductors, such as carbon and silicon, decreases with a temperature rise.
Electrical resistance is not the same as resistivity. While resistivity is a material property, resistance is the property of an object. The electrical resistance of a resistor is determined by the combination of the shape and the resistivity of the material. For example, a wirewound resistor with a long, thin wire has a higher resistance than a shorter and thicker wire.
Electrical conductivity is the inverse or reciprocal of electrical resistivity. It represents a material's ability to conduct electric current. The SI unit of electrical conductivity is Siemens per metre (S/m). Good electrical conductors have high conductivities and low resistivities, while good insulators or dielectrics have high resistivities and low conductivities. Semiconductors have intermediate values of both.
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Resistivity of common materials
Electrical resistivity is a fundamental property of a material that measures its electrical resistance, or how strongly it resists electric current. Resistivity is commonly represented by the Greek letter rho (ρ). The SI unit of electrical resistivity is the ohm-metre (Ω⋅m).
Every material has its own characteristic resistivity. For example, rubber has a far larger resistivity than copper. Resistivity is an intrinsic property and does not depend on the geometric properties of a material. This means that all pure copper (Cu) wires, irrespective of their shape and size, have the same resistivity.
The value of resistivity depends on the temperature of the material. Resistivity tabulations usually list values at 20°C. Resistivity of metallic conductors generally increases with a rise in temperature, while the resistivity of semiconductors, such as carbon and silicon, generally decreases with a temperature rise.
Nichrome, an alloy of nickel and chromium, is often used as a resistor wire material because of its high resistivity and resistance to oxidation at high temperatures. However, a disadvantage is that solder does not adhere to it.
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Frequently asked questions
Electrical resistivity is a fundamental property of a material that measures how strongly it resists the flow of electric current.
The SI unit of electrical resistivity is the ohm-meter (Ω⋅m).
Electrical resistance is the property of an object, whereas electrical resistivity is a property of the material that the object is made of.
Electrical conductivity is the inverse of electrical resistivity. It measures how well a material conducts electric current.
The resistivity of a material depends on the temperature of the material. Resistivity generally increases with a rise in temperature for metallic conductors and decreases with an increase in temperature for semiconductors.
