Trystan Casey
Electrical resistance, also known as specific electrical resistance, is the property of a material that opposes the flow of electric current. It is denoted by the letter 'R' and measured in ohms, represented by the symbol Ω. The higher the resistance, the lower the amount of current can pass through it. The resistance of a material depends on its length, cross-sectional area, and temperature. Electrical resistance is an important property as it is used to generate heat and has several applications in our daily lives.
| Characteristics | Values |
|---|---|
| Definition | The electrical resistance of an object is a measure of its opposition to the flow of electric current. |
| Symbol | R |
| Unit | Ohm (Ω) |
| Formulation | One Ω represents the electrical resistance between two points when a voltage of one volt is applied across the points, resulting in a current of one ampere, or amp. |
| Reciprocal Quantity | Electrical conductance |
| Factors Influencing Resistance | Material, length, cross-sectional area, and temperature |
| Factors Influencing Conductance | Size, shape, material, temperature, and strain |
| Materials with Zero Resistance | Superconductors |
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What You'll Learn
Electric resistivity
The resistivity of a material is influenced by its temperature and composition. Higher temperatures cause greater vibrations in the crystal lattice, leading to increased resistance. Additionally, the purity of the material is important, as a mixture of different ions can create irregularities and increase resistance. The value of resistivity also depends on the material's temperature; resistivity of metallic conductors generally increases with a rise in temperature, while resistivity of semiconductors, such as carbon and silicon, generally decreases with a temperature rise.
The inverse of resistivity is electrical conductivity (σ), which measures a material's ability to conduct an electric current. The SI unit of electrical conductivity is Siemens per meter (S/m), and the unit of resistivity is Ohm meters (Ωm). The relationship between resistivity and conductivity is important in understanding the electrical properties of materials.
Archie's Law describes the inverse relationship between resistivity (ρ) and porosity (φ) in a porous, clay-free medium with a non-conducting matrix. This law is particularly relevant in geophysics and hydrogeology, where it is used to calculate various parameters based on known measurements.
In summary, electric resistivity is a critical concept in understanding how materials resist electric current and how this resistance is influenced by factors such as temperature, composition, and porosity.
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Ohm's Law
Electrical resistance is the measure of a material's opposition to the flow of electric current. It is influenced by the material's properties, length, cross-sectional area, and temperature. Every material has an electrical resistance, and this is why conductors give out heat when a current passes through them.
> V = I x R
> Volts = Amps x Ohms
> V = A x Ω
Where:
- V = Voltage
- I = Current
- R = Resistance
- Ω = Ohms
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Conductors and insulators
Electrical resistance is a measure of how much an object opposes the flow of electric current. It is influenced by factors such as the material's properties, length, cross-sectional area, and temperature. The SI unit of electrical resistance is the ohm (Ω).
Now, conductors are substances in which electricity can flow. They offer very little resistance and allow electrons to move freely. The best electrical conductors are metals, as they have electrons in the outer layer of their atoms that are freely shared. The most conductive of all the elements is silver, but it is too rare and expensive to be used in most electrical equipment. The most common electrical conductor used today is copper, followed by aluminium.
On the other hand, insulators are materials that are resistant to the flow of electric current. They oppose the movement of electric charge. Insulators are important to keep us safe from electricity. For example, the wire that delivers electricity to your devices is covered with a rubber-like insulator to protect you from getting electrocuted. Other good insulators include glass, air, and paper.
In between conductors and insulators are semiconductors, which behave like conductors in certain conditions and like insulators in others. Their conductivity can be controlled, allowing current to flow in one direction or only under certain circumstances. The most common semiconductor in electronics is silicon.
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Measuring resistance
Electrical resistance is the property of an electrical component to resist the flow of electric current. It is influenced by the material's properties, length, cross-sectional area, and temperature. Every material has an electrical resistance, and this is why conductors give out heat when a current passes through them.
The unit of electrical resistance is the ohm, symbolised by Ω. Ohms are named after German physicist Georg Simon Ohm (1784-1854), who studied the relationship between voltage, current, and resistance.
The electrical resistance of an object is a measure of its opposition to the flow of electric current. It is measured in ohms, represented by the symbol Ω. One ohm represents the electrical resistance between two points when a voltage of one volt is applied across the points, resulting in a current of one ampere, or amp.
The resistance of an object depends on the material it is made of. Objects made of electrical insulators like rubber tend to have very high resistance and low conductance, while objects made of electrical conductors like metals tend to have very low resistance and high conductance.
The resistance of an object can be determined by measuring the circuit voltage and current, and then applying Ohm's Law. For example, if the circuit current is 3 amps instead of 4, the circuit resistance has increased from 60 Ω to 80 Ω (240 ÷ 3 = 80 Ω). The 20 Ω gain in total resistance could be caused by a loose or dirty connection or an open-coil section.
The resistance of an object can be measured using a digital multimeter or an ohmmeter. A multimeter is a multifunctional tool that can measure voltage, current, resistance, and other types of electrical measurements, while an ohmmeter only measures resistance.
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Superconductors
Electrical resistance is a measure of how much an object resists the flow of electric current. It is influenced by the material's properties, length, cross-sectional area, and temperature. All objects resist electric current to some degree, except for superconductors, which have zero resistance.
In a superconductor, the movement of electrons is highly coordinated, with electrons passed along from atom to atom in a synchronised manner, resulting in no collisions, resistance, or heat. The colder a material gets, the more organised the movement of electrons and nuclei becomes, which is why existing superconductors only work at extremely low temperatures. Most metallic superconductors, such as niobium-tin alloys, require cooling to temperatures near 4 Kelvin using liquid helium.
The phenomenon of superconductivity was discovered in 1911 by Dutch physicist Heike Kamerlingh Onnes, who observed that at a temperature of 4.2 Kelvin, the resistance of a material abruptly disappeared. Since then, superconductivity has been observed in various materials, including lead and niobium nitride. Theoretical work in the field has also led to important discoveries such as the Josephson effect, which has been exploited in superconducting devices like SQUIDs.
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Frequently asked questions
Electrical resistance is the opposition to the flow of electric current in a circuit. It is measured in ohms, represented by the symbol Ω.
Specific electrical resistance, or electrical resistivity, is a property of a material that measures its electrical resistance or how strongly it resists electric current. It is denoted by the Greek letter rho (ρ). The SI unit of electrical resistivity is the ohm-metre (Ω⋅m).
Resistance is the property of an electrical conductor to oppose or resist the flow of electric current. It is influenced by the material's properties, length, cross-sectional area, and temperature. Resistivity, on the other hand, is a fundamental property of a material that quantifies its resistance. It is defined as the resistance offered per unit length and unit cross-sectional area at a specific temperature.
Materials with low resistivity, such as metals, are good conductors of electricity and have low resistance. Materials with high resistivity, such as rubber, are insulators and have high resistance.
