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

K12 Standards

north-carolina-k-12-science-standard-course-of-study

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

מכפלת הזרם הזורם דרך מוליך והמתח לאורכו מכונה כוח חשמלי. יחידת SI של כוח חשמלי היא הוואט.
שקול הבדל פוטנציאלי בין מוליך. השדה החשמלי במוליך מכוון מפוטנציאלים גבוהים יותר לפוטנציאלים נמוכים יותר. מכיוון שהשינוי בהפרש הפוטנציאלים הוא שלילי, ניתן לקבוע את השדה החשמלי.
אם המטען חיובי, השדה החשמלי מפעיל כוח על המטען ומעביר אותו דרך המוליך.
העבודה הנעשית על המטען שווה למכפלת הכוח החשמלי ולמשך הפעלת הכוח.
הכוח המתפזר על ידי החומר בצורה של חום ואור שווה לקצב הזמן של שינוי העבודה.
במעגל עם נגד, הירידה הפוטנציאלית על פני הנגד מתפזרת כחום. על ידי היזכרות בחוק אוהם, ניתן לחשב את הכוח המתפזר על ידי הנגד.
ניתן ליצור קשר בין כוח, זרם, מתח והתנגדות עבור כל המכשירים האוהמיים.

<ol>
	<li>OpenStax. (2019). פיזיקה אוניברסיטאית כרך 2. [גרסת אינטרנט], עמ' 396 - 398. מקור: <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>

כוח חשמלי

<div style="direction:rtl">הספק חשמלי הוא מכפלה של זרם ומתח, המיוצגים ביחידות של ג'אול לשנייה, או וואט. לדוגמא, לרוב יש במכוניות שקע חשמל עזר אחד או יותר שבאמצעותו ניתן להטעין טלפון סלולרי או מכשירים אלקטרוניים אחרים. שקעים אלה עשויים להיות מדורגים ב-20 אמפר ו-12 וולט, כך שהמעגל יכול לספק הספק מרבי של 240 וואט. חשבו על נורת 25 וואט ונורה 60 וואט. המרה של אנרגיה חשמלית מייצרת חום ואור, בעוד שהאנרגיה הקינטית שאבדו האלקטרונים בהתנגשויות מומרת לאנרגיה הפנימית של המוליך והקרינה. לכן, נורת ה-60 וואט זוהרת יותר וחמה יותר מנורת ה-25 וואט. נתיך הוא מכשיר המגן על מעגל מפני עלייה פתאומית בחשמל. זה בעצם חתיכת חוט קצרה בין שני מגעים. במהלך תנודה בחשמל או בהספק, האנרגיה הקינטית של נושאי המטען—זרם— העוברים במוליך מומרת לאנרגיה תרמית במוליך. פיסת החוט בפתיל נמצאת במתח ובעלת נקודת התכה נמוכה, שנועדה להתחמם ולהישבר בזרם הנקוב. נתיכים פועלים במהירות, אך יש עיכוב זמן קטן בזמן שהחוט מתחמם ונשבר. לאחר שהפתיל נהרס, יש להחליפו מכיוון שהוא מגן על שאר המעגל מהספק גבוה. באופן דומה, מפסקי זרם מדורגים גם עבור זרם מרבי ונשארים פתוחים כדי להגן על המעגל, אך ניתן לאפס אותם.</div>

כוח חשמלי הוא תוצר של זרם ומתח, המיוצג ביחידות של ג'אול לשנייה, או וואט. לדוגמה, מכוניות לעתים קרובות יש אחד או יותר ...

Education

JoVE Core

פיזיקה

Unit 1

יחידה 1

Current and Resistance

זרם והתנגדות

KEY TERMS AND CONCEPTS

מונחים ומושגים מרכזיים

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

physics

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.

ohios-learning-standards-and-model-curriculum

Ohio’s Learning Standards and Model Curriculum

Electricity And Magnetism

DC circuits

Virginia  Standards of Learning

HIgh School

Physical Science

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

P-PS2-5

new-york-state-science-learning-standards

New York State Science Learning Standards

HS. Energy

HS-PS3-6.

Georgia Standards of Excellence

SP5.

Power in Circuits

Position and Displacement

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Average Velocity

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Instantaneous Velocity - I

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Instantaneous Velocity - II

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Average Acceleration

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Instantaneous Acceleration

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Velocity and Position by Graphical Method

Velocity and position can be calculated from the known function of acceleration as a function of time. The total area under the acceleration-time graph ...

Velocity and Position by Integral Method

If acceleration as a function of time is known, then velocity and position functions can be derived using integral calculus. For constant acceleration, ...

Use models (graphs, equations, diagrams) to infer motion in one dimension.

PS.Phy.1.1

Position and Displacement Vectors

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average-and-instantaneous-velocity-vectors

Average and Instantaneous Velocity Vectors

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Acceleration Vectors

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Direction of Acceleration Vectors

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Projectile Motion

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In&#160;uniform circular motion, the particle executing circular motion has a constant speed, and the circle is at a fixed radius. However, not all ...

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Use models (graphs, equations, diagrams) to infer motion in two dimensions.

PS.Phy.1.2

Force

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Types of Forces

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Drawing Free-body Diagrams: Rules

The first step in describing and analyzing most phenomena in physics involves the careful drawing of a free-body diagram. Free-body diagrams are useful in ...

Free Body Diagrams: Examples

Solving problems that involve forces is easy using free-body diagrams. A free-body diagram is a sketch showing all the external forces that are acting on ...

Use free body models to qualitatively and quantitatively analyze systems of forces in one dimension and two dimensions.

PS.Phy.2.1

Newton's First Law: Introduction

Motion draws our attention. Motion itself can be beautiful, causing us to marvel at the forces needed to create spectacular sights, such as that of a ...

Newton's First Law: Application

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first-law-particles-in-one-dimensional-equilibrium

First Law: Particles in One-dimensional Equilibrium

Newton&#39;s first law of motion states that a body at rest remains at rest, or if in motion, remains in motion at constant velocity, unless acted on by a ...

first-law-particles-in-two-dimensional-equilibrium

First Law: Particles in Two-dimensional Equilibrium

Recall that a particle in equilibrium is one for which the external forces are balanced. Static equilibrium involves objects at rest, and dynamic ...

Second Law: Motion under Same Force

Newton&#39;s laws can be applied to bodies at rest and bodies in motion. Newton&#39;s first law is applied to bodies in equilibrium, whereas the second ...

Carry out investigations to explain the interactions of forces on an object according to Newton's Laws of Motion.

PS.Phy.2.2

Analyze the motion of objects using time, distance, displacement, speed, velocity, and acceleration.

Power Limits in Electrical Circuits

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