Otis Singleton
Resistance is a measure of the opposition to the flow of current in an electrical circuit. It is influenced by the material's properties, length, cross-sectional area, and temperature. Low electrical resistance means that the current flow is high. Materials like copper wire and other metals have low resistance and are considered conductors. The amount of current in a circuit depends on the voltage and the resistance that opposes the current flow. Resistance is measured in ohms, symbolized by the Greek letter omega (Ω).
| Characteristics | Values |
|---|---|
| Definition | Low electrical resistance means that a material does not resist the flow of electrons. |
| Formula | V (voltage) = I (current) x R (resistance) |
| Unit | Ohms, symbolized by the Greek letter omega (Ω) |
| Factors Affecting Resistance | Material type, length, cross-sectional area, and temperature |
| Examples of Low-Resistance Materials | Copper wire, metals |
| Examples of High-Resistance Materials | Rubber, plastic, steel, Teflon |
| Use Cases | Low resistance is desirable in conductors used to transmit electricity efficiently. |
| Measuring Instrument | Ohmmeter, digital multimeter |
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What You'll Learn
Low resistance materials
Conductors, such as metals, tend to have very low resistance and high conductance. Examples of low resistance materials include silver, copper, gold, and aluminum. Silver has the lowest resistivity, but due to its high cost, it is not commonly used as a conducting material. Copper is a more affordable alternative and is widely used in electrical applications. However, it is important to note that the resistivity of copper is about 1030 times higher than that of Teflon.
The properties of low resistance materials are desirable in electrical engineering for efficient power transmission and the creation of durable machines, equipment, and devices. These materials offer minimal resistance to electric current, reducing power loss and minimizing heat generation. Additionally, low resistance materials exhibit stable temperature performance, high melting points, mechanical strength, ductility, and corrosion resistance.
The type of material, its purity, temperature, and shape and size all influence its resistivity or conductivity. Metals generally have lower resistivity than non-metals due to their free electrons, while non-metals have tightly bound electrons that resist electric current. Impurities in materials, even those with low resistivity, can increase overall resistivity by disrupting the flow of electrons.
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How resistance is measured
Electrical resistance is measured in ohms, represented by the symbol Ω. 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. The scientific symbol for electrical resistance, Ω, is the Greek letter omega. However, electricians and practical wiring books often use an "R" to represent resistance.
There are two methods for measuring electrical resistance: constant current or constant voltage. The constant current technique involves sourcing a known current through an unknown resistance and measuring the resulting voltage. This technique is generally used for resistance values below 200M ohms. The constant voltage technique, on the other hand, involves sourcing a known voltage across an unknown resistance and measuring the resulting current. This approach is used for high resistance (1e8 to 1e16) measurement applications.
To measure resistance, you can use either a multimeter or an ohmmeter. A multimeter is a multifunctional tool that can measure voltage, current, resistance, and other electrical measurements, depending on its style. An ohmmeter, on the other hand, is a tool that only measures resistance.
When measuring resistance, it is important to note that it cannot be measured in an operating circuit. Therefore, troubleshooting technicians often determine resistance by taking voltage and current measurements and applying Ohm's Law. This law states that the voltage (V) across a circuit is equal to the current (I) flowing through it multiplied by the resistance (R). That is, V = I x R. If the resistance is unknown, the formula can be rearranged to R = V/I.
Additionally, when measuring resistance, it is important to ensure good contact between the test leads and the circuit. For very low-resistance measurements, the relative mode (REL) should be used. This mode automatically subtracts the test lead resistance, which typically ranges from 0.2 Ω to 0.5 Ω. If the test leads touch, the display should show 0 Ω. Other factors that can affect resistance readings include foreign substances (such as dirt, solder flux, or oil), body contact with the metal ends of the test leads, or parallel circuit paths.
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Factors influencing resistance
Low electrical resistance means that a substance or material easily allows the flow of electric current. This is because the atoms and molecules of the substance do not significantly obstruct the flow of electrons. The opposite of low resistance is high resistance, where a substance or material prevents the flow of electric current.
There are several factors that influence resistance.
Material
The type of material is a significant factor in determining resistance. Materials with high conductivity, such as metals, tend to have low resistance, while insulators like rubber have high resistance. The difference in resistance between materials is due to their microscopic structure and electron configuration, which is quantified by a property called resistivity. For example, copper has lower resistance than steel, and Teflon has much lower conductivity than copper.
Length
The length of a conductor also affects resistance. Longer conductors cause more resistance, as there is more resistance for the current to overcome when it travels a longer distance. Therefore, longer wires have higher resistance than shorter ones.
Cross-sectional Area
The cross-sectional area of a conductor is another factor influencing resistance. Thicker wires have lower resistance than thinner wires, as the resistance is inversely proportional to the cross-sectional area.
Temperature
Temperature changes can also impact resistance. In conductors, an increase in temperature typically leads to an increase in resistance, while in semiconductors, an increase in temperature can decrease resistance. Additionally, in semiconductors, resistivity changes when exposed to light.
Current Frequency
The frequency of the current can affect resistance as it influences the movement of electrons within the conductor.
Impurities
The presence of impurities in a material can also impact its resistance. For example, moisture-damaged insulators can lead to increased resistance.
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Ohm's Law
Low electrical resistance means that electricity can flow through an object with ease. Objects made of electrical conductors like metals tend to have very low resistance and high conductance. On the other hand, objects made of electrical insulators like rubber tend to have very high resistance and low conductance.
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Resistors
Resistance is the opposition to electrical current. When electricity flows through any resistor, energy is dissipated in the form of heat. If the heat becomes intense enough, the resistor may glow. For example, in an incandescent lightbulb, the electricity flowing through the filament, or the tiny wires inside the bulb, causes them to glow white-hot. Resistors can be made of various compounds and forms, and they are also implemented within integrated circuits. The electrical function of a resistor is specified by its resistance.
The resistance of a given object depends primarily on two factors: the material it is made of and its shape. For a given material, the resistance is inversely proportional to the cross-sectional area; for example, a thick copper wire has lower resistance than a thin copper wire. Also, for a given material, the resistance is proportional to the length; for example, a long copper wire has higher resistance than a short copper wire. The difference in resistance between different materials is related to their microscopic structure and electron configuration and is quantified by a property called resistivity.
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Frequently asked questions
Low electrical resistance means that there is minimal opposition to the flow of electric current within an electrical circuit. Materials with low resistance are known as conductors and allow electrons to move easily. Examples of materials with low resistance include metals and copper wire.
Low resistance results in a higher current flow. When measuring low resistance in materials, you can decrease the voltage because the current will flow more naturally.
Low electrical resistance is beneficial when trying to transmit electricity efficiently from one place to another through a conductor. It is also useful in electronic circuits, where resistors are needed to ensure that the current flows at an appropriate level.
