Beatrice Lang
Electrical resistance is the opposition to the flow of current in a circuit, measured in ohms (Ω). Every material has an electrical resistance, and this is why conductors give out heat when an electric current passes through them. The resistance of an object depends largely 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. Resistors are important in electrical circuits because they resist current in a precise and controllable way.
| Characteristics | Values |
|---|---|
| Definition | Opposition to the flow of electric current in a circuit |
| Formula | Resistance (R) equals voltage (V) divided by current (I) |
| Unit | Ohm (Ω) |
| Reciprocal Quantity | Electrical conductance |
| Factors Affecting Resistance | Material, length, cross-sectional area, temperature |
| Resistivity | A qualitative measurement of a material's ability to resist flowing electric current |
| Superconductors | Materials with zero resistance and infinite conductance |
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What You'll Learn
- Electrical resistance is the opposition to the flow of current in a circuit
- Resistance is measured in ohms (Ω)
- Resistance depends on a material's length, cross-sectional area, and temperature
- Resistors resist current in a precise and controllable way
- Resistance is important in consumer devices to convert electrical energy to heat
Electrical resistance is the opposition to the flow of current in a circuit
The electrical resistance of an object is a measure of its opposition to the flow of electric current. The reciprocal quantity is electrical conductance, which measures the ease with which an electric current passes. Electrical resistance shares some conceptual parallels with mechanical friction. For example, in the same way that it is more difficult to push water through a long, narrow pipe than a wide, short pipe, a long, thin copper wire has higher resistance (lower conductance) than a short, thick copper wire.
The SI unit of electrical resistance is the ohm (Ω), while electrical conductance is measured in siemens (S). The resistance of an object depends largely 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.
Resistance depends on a material's length, cross-sectional area, and temperature. For example, electrical resistance is directly proportional to the length (L) of the conductor and inversely proportional to the cross-sectional area (A). If the cross-sectional area of an electric cord is increased, there will be a reduction in resistance.
Resistors are important components in electrical circuits because they resist current in a precise and controllable way. The unit that is used to specify the resistance of a resistor is the ohm. A resistor with very low resistance could be considered a conductor, while a resistor with resistance in the tens of millions of ohms will function like an insulator.
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Resistance is measured in ohms (Ω)
Resistance is a measure of how much an object opposes the flow of electric current through it. The SI unit of electrical resistance is the ohm, represented by the Greek letter omega (Ω). One ohm of resistance is equal to one volt per ampere, or the amount of resistance that will produce a current of one ampere when subjected to a potential of one volt.
Resistance is measured using an ohmmeter, which displays zero ohms when the test leads are clipped together, and infinite or over-limit resistance when the leads are left open. When a resistance is placed between the leads, the readout will increase according to how much current the resistance allows to flow. To measure resistance, the component to be tested is isolated and the test probes are plugged into the appropriate jacks. The ohms function is then selected, and the probes are touched together to check the leads, connections, and battery life. With the leads apart, the meter should display OL or I, depending on the manufacturer. The tips of the probes are then connected across the break in the component or circuit, and the resistance can be read on the display unit.
Resistance can be measured using one of two methods: constant current or constant voltage. The constant current technique involves sourcing a known current through an unknown resistance and measuring the resulting voltage, and is generally used for resistance values below 200 million ohms. The constant voltage technique, on the other hand, involves applying a known voltage across an unknown resistance and measuring the resulting current, and is used for high resistance measurements.
Resistance is an important factor in electrical circuits, and resistors are used to control the flow of current. A resistor with very low resistance, such as less than one ohm, can be considered a conductor, while a resistor with resistance in the tens of millions of ohms will function as an insulator. Moderate values of resistance do not fit neatly into either of these categories.
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Resistance depends on a material's length, cross-sectional area, and temperature
Electrical resistance is a measure of how much an object opposes the flow of electric current through it. The SI unit of electrical resistance is the ohm (Ω), and the reciprocal quantity of resistance is electrical conductance, which measures how easily an electric current passes through an object.
The relationship between resistance and length can be expressed using the formula: R = 𝜌L/A, where R is the resistance, L is the length, A is the cross-sectional area, and 𝜌 is the resistivity of the material. This formula demonstrates that resistance increases with length, as a longer material will have a larger denominator in the formula, resulting in a smaller overall value for resistance.
Additionally, the cross-sectional area of a material also affects its resistance. A material with a smaller cross-sectional area will have higher resistance compared to a material with a larger cross-sectional area, assuming all other factors remain constant. This relationship is similar to how water flows more easily through a wide, short pipe than a long, narrow one.
Finally, the temperature of a material can also impact its resistance. Resistivity, denoted as 𝜌 or rho, is an intrinsic property of a material that measures its resistance to the flow of electric current. Resistivity is indirectly proportional to temperature, meaning that as temperature increases, resistivity decreases, and vice versa. However, this relationship is not true for all materials. For example, insulators and semiconductors exhibit the opposite behaviour, with their resistivities increasing as temperatures rise due to an increase in electron collisions.
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Resistors resist current in a precise and controllable way
Electrical resistance is a measure of a substance's opposition to the flow of electric current. The SI unit of electrical resistance is the ohm (Ω). The reciprocal of electrical resistance is electrical conductance, which measures how easily electric current passes through a substance.
Resistance is influenced by the material a substance is made of, its size, and its shape. For instance, a long, thin copper wire has higher resistance than a short, thick copper wire of the same material. Similarly, a pipe filled with hair restricts water flow more than a clean pipe, just as a steel wire impedes electron flow more than a copper wire of the same shape and size.
Resistors are electrical components that introduce a precise and controlled amount of resistance into a circuit. They are constructed out of materials such as carbon, metal, or metal-oxide film. Resistors are essential to almost every electrical circuit, controlling the flow of electrical current to sensitive components and protecting them from voltage spikes.
The unit of measurement for resistance in a resistor is the ohm. A resistor with very low resistance, such as less than 1 ohm, would be considered a conductor, while a resistor with resistance in the tens of millions of ohms would function like an insulator. Resistors can be wired into a circuit in series, where the same current flows through them, or in parallel, where the same voltage is applied to them.
The number of turns of wire in a resistor controls the resistance very precisely. For example, in a wire-wound resistor, the more turns of wire, and the thinner the wire, the higher the resistance. Resistors can also be made of carbon film, which is a cheaper alternative to wire-wound resistors.
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Resistance is important in consumer devices to convert electrical energy to heat
Electrical resistance is a measure of a substance's opposition to the flow of electric current. It is denoted by the Greek letter omega (Ω) and is measured in ohms. Every material has a certain electrical resistance, and this is why conductors give out heat when an electric current passes through them.
Resistance is also used in sound systems to control the flow of electrical signals to the speakers, thereby affecting the volume and quality of the sound. By adjusting the resistance, one can change the volume of the music.
Resistance is an important factor in electronic circuits, as it controls the flow of electricity, ensuring that devices operate safely and efficiently. Resistors are one of the most important electronic components and are used to limit the amount of current going to an LED, for instance.
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