Name: factors that affect electrical resistance
Uploaded: 2023-04-30T12:39:00.000Z
Duration: 1 min 19 s
Channel: JoVE

K12 Standards

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North Carolina K-12 Science Standard Course of Study

9-12

Physical Science

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Motion and Stability- Forces and Interactions

PS.PSc.6.2

Resistance

Kiedy prąd przepływa przez obwód, zderzenia elektronów i atomów w przewodzie powodują opór ruchu elektronów, mierzony w omach.
Rezystancja elektryczna obwodu to stosunek przyłożonego napięcia do przepływającego przez niego prądu. Rezystancja zależy również od rezystywności materiału i jest równoważna rezystywności materiału pomnożonej przez długość podzielonej przez pole przekroju poprzecznego drutu.
Temperatura wpływa na rezystancję materiałów i można ją modelować za pomocą równania rezystywności.
Element w obwodzie, który zmniejsza przepływ prądu, jest znany jako rezystor, reprezentowany przez dwa symbole dostarczone przez American National Standard Institute i Międzynarodową Komisję Elektrotechniczną.
Węgiel jest najczęstszym materiałem używanym do produkcji rezystorów. Ścieżki węglowe są owinięte wokół ceramicznego rdzenia, który jest połączony z dwoma miedzianymi przewodami i oznaczony czterema paskami w celu identyfikacji rezystora.
Pierwsze dwa kolorowe paski reprezentują pierwsze dwie cyfry oporu, podczas gdy trzeci i czwarty kolor reprezentują jego mnożnik i tolerancję.

<ol>
	<li>Protokół OpenStax. (2019). Fizyka uniwersytecka Vol. 2. [Wersja internetowa], str. 396–398. Źródło: <a href="https://openstax.org/books/university-physics-volume-2/pages/9-3-resistivity-and-resistance">https://openstax.org/books/university-physics-volume-2/pages/9-3-resistivity-and-resistance</a></li>
</ol>

opór

Kiedy prąd przepływa przez dowolny przewodnik, powoduje on pewne trudności w przepływie prądu. Miarą tej trudności jest opór materiału i jest reprezentowany przez R. Każdy materiał ma swój własny opór. W przypadku przewodników ciepło jest emitowane za każdym razem, gdy przepływa przez nie prąd. Opór zależy od rezystywności materiału. Rezystywność jest cechą materiału użytego do produkcji komponentów elektrycznych, podczas gdy rezystancja jest cechą samego komponentu.

Aby obliczyć rezystancję, weź pod uwagę odcinek przewodzącego drutu o polu przekroju poprzecznego A, długości L i oporności L;. Bateria jest podłączona do przewodnika, zapewniając różnicę potencjałów wynoszącą V. Różnica potencjałów wytwarza pole elektryczne proporcjonalne do gęstości prądu:

<img alt="Równanie1" src="/files/ftp_upload/13747/13747_Equation_1.svg" style="text-align: center; height: 13px;" />

Wielkość pola elektrycznego w odcinku przewodnika jest równa napięciu podzielonemu przez długość, a wielkość gęstości prądu jest równa prądowi podzielonemu przez pole przekroju poprzecznego. Podstawiając wartości i pamiętając, że pole elektryczne jest proporcjonalne do rezystywności i gęstości prądu, można ustalić zależność między napięciem i prądem:

<img alt="Równanie2" src="/files/ftp_upload/13747/13747_Equation_2.svg" style="text-align: center; height: 26px;" />

Rezystancję materiału można zdefiniować jako stosunek napięcia do przepływającego przez niego prądu i wyraża się ją w omach. Opór cylindrycznego odcinka przewodnika jest równy oporności materiału pomnożonej przez długość podzieloną przez pole:

<img alt="Równanie3" src="/files/ftp_upload/13747/13747_Equation_3.svg" style="text-align: center; height: 26px;" />

Opór obiektu zależy również od temperatury. W przypadku danego cylindra, jeśli długość i powierzchnia nie zmieniają się znacząco wraz z temperaturą, rezystancja materiału ma taką samą zależność temperaturową jak rezystywność:

<img alt="Równanie4" src="/files/ftp_upload/13747/13747_Equation_4.svg" style="text-align: center; height: 13px;" />

gdzie R0'to pierwotna rezystancja w temperaturze pokojowej, Rto rezystancja po zmianie temperatury, a ` 593; to współczynnik temperaturowy materiału.

Opór

Kiedy prąd przepływa przez dowolny przewodnik, przewodnik powoduje pewien poziom trudności w przepływie prądu. Miara tej trudności jest znana...

Education

JoVE Core

Physics

Fizyka

Unit 1

Jednostka 1

Current and Resistance

Natężenie prądu i rezystancja

KEY TERMS AND CONCEPTS

Kluczowe terminy i pojęcia

factors that affect electrical resistance

Electrical resistance describes how much a conductor opposes the flow of current. It is represented by R. When current passes through a conductor, heat is also produced. Resistance is tied to the material’s resistivity, which is a property of the material used to make an electrical component.

Resistance is different from resistivity. Resistivity belongs to the material itself, while resistance belongs to the finished component. To study this relationship, consider a wire with length L, cross-sectional area A, and resistivity ρ. If a battery provides a potential difference ΔV across the wire, the voltage creates an electric field in the conductor.

The electric field across the wire segment equals the voltage divided by the length. The current density equals the current divided by the cross-sectional area. Because the electric field is proportional to resistivity and current density, these values can be combined to relate voltage and current. Resistance is then defined as the ratio of voltage to current and is measured in ohms.

For a cylindrical conductor, resistance equals resistivity multiplied by length divided by area. Resistance also changes with temperature. If the length and area stay nearly the same as temperature changes, the resistance follows the same temperature dependence as the resistivity. In that case, R0 is the original resistance at room temperature, R is the resistance after the temperature change, and α is the temperature coefficient of the material.

Factors That Affect Electrical Resistance

factors-that-affect-electrical-resistance

electrical current

Current Flow in Simple Circuits

Electrical current is the flow of charge in a circuit. A large current means a large amount of charge moves through a wire in a short time. A small current means only a small amount of charge moves through the circuit over a longer time. Examples include the current needed to run a refrigerator and the smaller current used by a handheld calculator. The SI unit for current is the ampere, or amp. It is named for the French physicist André-Marie Ampère (1775–1836). One ampere means one coulomb of...

drift velocity

Electrical Current and Electron Drift

Electrical current in a conductor depends on moving charges and the tiny drift speed of those charges. When a free charge enters a wire, it pushes nearby charges ahead because like charges repel each other. That push spreads through the material very quickly, so the electrical signal moves through the system at nearly the speed of light. This fast signal is not the same as the slow motion of each charge. It is a rapidly spreading change in the electric field, often described as an electrical...

current density

Current Density in Wires and Solutions

Current density describes how much electric current passes through a given cross-sectional area. It helps show not just the size of the current, but also how it is distributed through a conductor. The current density can change from point to point because the local charge flow can vary. If the current flow is uniform, the amount of current is the same at every point along the conductor, even when the conductor’s area changes. Current density is measured in amperes per square meter. Its...

resistivity

Resistivity in Conductors and Insulators

Resistivity describes how much a material opposes electric current. When a voltage is applied to a conductor, an electric field forms. The charges in the conductor feel that force, and a current density develops. In some materials, including metals at a given temperature, the current density is approximately proportional to the electric field. In those cases, current density can be modeled with conductivity, written as sigma. Electrical conductivity is measured in (ohm·m)^−1. It tells how well...

resistance

Electrical resistance describes how much a conductor opposes the flow of current. It is represented by R. When current passes through a conductor, heat is also produced. Resistance is tied to the material’s resistivity, which is a property of the material used to make an electrical component. Resistance is different from resistivity. Resistivity belongs to the material itself, while resistance belongs to the finished component. To study this relationship, consider a wire with length L,...

ohm's law

Measuring Current, Voltage, and Resistance

Ohm's law describes the relationship between current, voltage, and resistance in many materials. In these cases, the current through a substance is directly proportional to the voltage applied to it. The idea was first shown experimentally by German physicist Georg Simon Ohm, who studied current in a metal wire. A material, component, or device that follows this pattern is called ohmic. An ohmic component has a current that increases in step with voltage. A material or component that does not...

non-ohmic devices

Diode Current and Reverse Bias

A diode is a nonohmic circuit element that makes current and voltage behave differently from Ohm’s law. In most substances, current is proportional to the voltage applied, but a diode does not show a linear current-voltage relationship. A diode is a semiconducting device with two terminals: an anode, which is the positive terminal, and a cathode, which is the negative terminal. It allows current to flow in only one direction. In a simple circuit with a battery, a diode, and a resistor, the...

electrical power

Power Limits in Electrical Circuits

Electrical power in a circuit depends on current and voltage. It is the product of these two values and is measured in watts, or joules per second. That relationship helps explain how much energy a circuit can deliver. A car’s auxiliary power outlet is one real-world example. Some outlets are rated at 20 amps and 12 volts, so they can deliver a maximum of 240 watts. That rating shows the upper limit of power the circuit can provide to devices such as a cell phone charger. Bulb wattage also...

electrical energy

Cutting Electric Bills with Efficient Lighting

Electrical energy is the energy transferred when electrons move from one point to another. The longer an appliance is used, the more electrical energy it consumes. If power stays constant, electrical energy equals the power used by the device times the time it runs. That is why longer use leads to a higher electric bill. Electric bills measure this energy in kilowatt-hours. One kilowatt-hour is equal to 3.6 × 10^6 joules. You can lower electrical energy use by cutting the time an appliance...

continuity equation

Charge Conservation and Current Flow

Charge conservation and current flow are linked through the continuity equation. The current density is the amount of current flowing per unit cross-sectional area. The current through a surface can be written as a surface integral of the current density. The conservation of charge says that the total current leaving a volume equals the rate at which charge inside that volume decreases. The total charge can be written using volume charge density, which is a space function. Because of this, the...

boundary conditions for current density

Current Density at Conductivity Boundaries

Current density at a boundary changes when two conducting materials have different electrical conductivities. The normal component of current density stays continuous across the interface. The tangential component, which runs along the surface, becomes discontinuous across the boundary. Consider two conducting media with conductivities σ1 and σ2 separated by an interface. At point P1 in medium 1, the steady current density makes an angle α1 with the normal. At point P2 in medium 2, the current...

electrical conductivity

Resistance and Ohm's Law in Conductors

Resistance and Ohm's law help explain how electric current moves through a conductor. In a perfect conductor, the electric field inside is zero because free electrons move to cancel it. Any extra charge then stays on the surface. In a practical conductor, an applied electric field can remain in place. That field drives electrons through the material and creates a current. The current density, which is current per unit area, is related to the electric field. More generally, it is related to the...

theory of metallic conduction

Electron Drift in Metallic Conduction

Electron drift in metallic conduction explains how free electrons move through a conductor. A classical model can describe this motion closely, even though quantum mechanics gives the best overall picture. This model is called the theory of metallic conduction. In this theory, Newton's second law is used to find the acceleration of an electron when an electric field is applied. The electron's velocity is then found from that acceleration. The electron travels through a crystal of positive ions...

key terms and concepts

Learn how resistance depends on resistivity, wire length, cross-sectional area, voltage, current, and temperature in conductors and electrical circuits.

Factors That Affect Electrical Resistance | JoVE K12

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Ohio’s Learning Standards and Model Curriculum

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Waves and Their Applications in Technologies for Information Transfer

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Ohm’s Law

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Factors That Affect Electrical Resistance

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