Name: power limits in electrical circuits
Uploaded: 2023-04-30T12:39:15.000Z
Duration: 1 min 7 s
Channel: JoVE

K12 Standards

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North Carolina K-12 Science Standard Course of Study

9-12

Physics

motion-and-stability-forces-and-interactions

Motion and Stability- Forces and Interactions

PS.Phy.4.3

Electrical Power

Das Produkt aus dem Strom, der durch einen Leiter fließt, und der Spannung, die über ihn fließt, wird als elektrische Energie bezeichnet. Die SI-Einheit der elektrischen Leistung ist das Watt.
Betrachten Sie eine Potentialdifferenz über einen Leiter. Das elektrische Feld in einem Leiter wird von höheren zu niedrigeren Potentialen gelenkt. Da die Änderung der Potentialdifferenz negativ ist, kann das elektrische Feld bestimmt werden.
Ist die Ladung positiv, übt das elektrische Feld eine Kraft auf die Ladung aus und bewegt sie durch den Leiter.
Die Arbeit, die an der Ladung geleistet wird, ist gleich dem Produkt aus der elektrischen Kraft und der Länge, in der die Kraft ausgeübt wird.
Die vom Material in Form von Wärme und Licht abgegebene Leistung entspricht der Zeitrate der Veränderung des Werkes.
In einer Schaltung mit einem Widerstand wird der Potentialabfall über den Widerstand als Wärme abgeführt. Durch Aufrufen des Ohmschen Gesetzes kann die vom Widerstand abgegebene Leistung berechnet werden.
Für alle ohmschen Bauelemente kann eine Beziehung zwischen Leistung, Strom, Spannung und Widerstand hergestellt werden.

<ol>
	<li>OpenStax. (2019). Universitätsphysik Vol. 2. [Web-Version], Seite 396 - 398. Abgerufen von <a href="https://openstax.org/books/university-physics-volume-2/pages/9-5-electrical-energy-and-power">https://openstax.org/books/university-physics-volume-2/pages/9-5-electrical-energy-and-power</a></li>
</ol>

elektrische leistung

Die elektrische Leistung ist das Produkt aus Stromstärke und Spannung, dargestellt in Einheiten von Joule pro Sekunde oder Watt. Zum Beispiel haben Autos oft eine oder mehrere zusätzliche Stromanschlüsse, mit denen Sie ein Handy oder andere elektronische Geräte aufladen können. Diese Anschlüsse können mit 20 Ampere und 12 Volt bewertet sein, so dass der Stromkreis eine maximale Leistung von 240 Watt liefern kann. Betrachten Sie eine 25 Watt Glühbirne und eine 60 Watt Glühbirne. Die Umwandlung von elektrischer Energie erzeugt Wärme und Licht, während die kinetische Energie, die bei Kollisionen von Elektronen verloren geht, in die innere Energie des Leiters und in Strahlung umgewandelt wird. Daher leuchtet die 60 Watt Glühbirne heller und wärmer als die 25 Watt Glühbirne.

Eine Sicherung ist ein Gerät, das einen Stromkreis vor einem plötzlichen Anstieg der elektrischen Leistung schützt. Es handelt sich im Wesentlichen um ein kurzes Stück Draht zwischen zwei Kontakten. Bei einer Schwankung in der Elektrizität oder der Leistung wird die kinetische Energie der Ladungsträger - Strom - die durch einen Leiter fließt, in thermische Energie im Leiter umgewandelt. Das Stück Draht in der Sicherung steht unter Spannung und hat einen niedrigen Schmelzpunkt. Es ist so konzipiert, dass es sich bei der bewerteten Stromstärke erwärmt und bricht. Sicherungen reagieren schnell, aber es gibt eine kleine Zeitverzögerung, während der Draht sich erhitzt und bricht. Sobald die Sicherung zerstört ist, muss sie ersetzt werden, da sie den Rest des Stromkreises vor hoher Leistung schützt. Ähnlich sind auch Leitungsschutzschalter für eine maximale Stromstärke bewertet und bleiben geöffnet, um den Stromkreis zu schützen, können aber zurückgesetzt werden.

Elektrische Leistung

Die elektrische Leistung ist das Produkt aus Strom und Spannung, dargestellt in Einheiten von Joule pro Sekunde oder Watt. Zum Beispiel haben Autos oft einen oder mehrere ...

Education

Lehre

JoVE Core

Physik

Unit 1

Einheit 1

Current and Resistance

Strom und Widerstand

KEY TERMS AND CONCEPTS

KERNBEGRIFFE UND KONZEPTE

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 shows how power affects energy conversion. A 25 watt bulb and a 60 watt bulb both turn electrical energy into heat and light. The electrons lose kinetic energy in collisions, and that energy becomes internal energy in the conductor and radiation. As a result, the 60 watt bulb glows brighter and feels warmer than the 25 watt bulb.

Fuses and circuit breakers protect circuits from sudden rises in electric power. A fuse is a short wire between two contacts. When current fluctuates, the charge carriers in the conductor convert kinetic energy into thermal energy. The fuse wire is under tension and has a low melting point, so it heats up and breaks at its rated current. Fuses work quickly, but they need a short time to heat and fail, and they must be replaced after they blow. Circuit breakers also have a maximum current rating, but they stay open to protect the circuit and can be reset.

Power Limits in Electrical Circuits

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

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,...

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

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 current and voltage determine electrical power, why higher-watt bulbs glow brighter, and how fuses and circuit breakers protect circuits.

Power Limits in Electrical Circuits | JoVE K12

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JoVE Core Physics introduces the theory and application of fundamental physics topics, including kinematics, dynamics, fluid mechanics, statics, waves, and acoustics, with concise and easy-to-understand animated videos. Additionally, the scientist-in-action videos demonstrate the application of related concepts in classical and original research experiments performed in today's laboratories worldwide.

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Ohio’s Learning Standards and Model Curriculum

Electricity And Magnetism

DC circuits

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PS.9

PS.9.c

PH.8

PH.8.d

Arizona Science Standards

High School

HS+Phy.P4

HS+Phy.P4U1.8

Alabama Course of Study Science

Energy

9-12.P.2.6.b

Next Generation Science Standards

Motion and Stability: Forces and Interactions

HS-PS2-5

Florida Department of Education

SC.912.P.10

SC.912.P.10.15

Texas Essential Knowledge and Skills

PHYS.6

PHYS.6.E

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South Carolina College and Career Ready Science Standards

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New York State Science Learning Standards

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Georgia Standards of Excellence

SP5.

Power in Circuits

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PS.Phy.2.2

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Power Limits in Electrical Circuits

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