Download presentation on the topic of the work of electric current. Electric power. What formula is used to determine power?

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WORK OF ELECTRIC CURRENT Work electric current shows how much work was done by the electric field when moving charges along a conductor. The work of an electric current is equal to the product of the current strength and the voltage and the time the current flows in the circuit. SI unit for measuring the work of electric current: [A] = 1 J = 1A B c

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POWER OF ELECTRIC CURRENT The power of electric current shows the work done by the current per unit time and is equal to the ratio of the work done to the time during which this work was done. (power in mechanics is usually denoted by the letter N, in electrical engineering by the letter P) since A = IUt, then the power of the electric current is equal to: Unit of electric current power in the SI system: [P] = 1 W (watt) = 1 A. B

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LEARN IT, IT WILL BE USEFUL! When calculating the work of electric current, an off-system multiple of the unit of work of electric current is often used: 1 kWh (kilowatt-hour). 1 kWh = ..................... Watts = 3,600,000 J In each apartment, special electricity meters are installed in each apartment to account for consumed electricity, which show the work of electric current performed over a certain period of time when various household electrical appliances. These meters show the work of electric current (electricity consumption) in “kWh”. 1 kWh of energy allows you to smelt 20 tons of cast iron

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WOW, INTERESTING At one time, J. Watt proposed such a unit as “horsepower” as a unit of power. This unit of measurement has survived to this day. But in England in 1882, the British Association of Engineers decided to assign the name of J. Watt to a unit of power. Now the name James Watt can be read on any light bulb. This was the first case of appropriation in the history of technology own name unit of measurement. From this incident the tradition of assigning proper names to units of measurement began.

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They say that... one of Watt's steam engines was bought by a brewer to replace the horse that drove the water pump. When choosing required power steam engine the brewer defined horse labor as eight hours of non-stop work until the horse was completely exhausted. The calculation showed that every second the horse raised 75 kg of water to a height of 1 meter, which was taken as a unit of power of 1 horsepower.

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LET'S ALL RUN TO THE TASKS! Two electric lamps, whose power is 40 and 100 W, are designed for the same voltage. Compare the filament resistances of both lamps. The room is lit with 40 electric lamps from a flashlight, connected in series and powered from the city network. After one lamp burned out, the remaining 39 were again connected in series and plugged into the network. When was the room brighter: with 40 or 39 lamps? Series-connected copper and iron wires of the same length and cross-section are connected to the battery. Which one will stand out? large quantity warmth for same time?

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Solve the problem An electric lamp is connected to a circuit with a voltage of 125 V, the current in which is 0.4 A. Find the current power in the lamp. (Calculate the work done by the current in 10 minutes)

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Slide captions:

Work and power of electric current

Repetition of I U R and Ohm's law New material: A measurement A power (P) maximum P Questions 1 2 3 Tasks 1 2 D/z table

The current strength is denoted by the letter I, measured in SI in amperes (A). The current strength I is equal to the ratio of the electric charge q passing through the cross section of the conductor to the time of its passage: I= q/t. The current strength is measured by an ammeter, it symbol in the circuits, the ammeter is connected in series in the circuit. A

Job electric field creating a current is called the work of the current. Voltage U is the work done by an electric current to move a unit electric charge: U=A/q ​​The unit of voltage is the volt (V). The voltage on a section of the circuit is measured with a voltmeter; its symbol in the diagrams is a voltmeter connected to the circuit parallel to the consumer. V V

The higher the voltage, the stronger the effect of the electric field on the particles and the more power current in the circuit. For a wide class of conductors (including metals), the current in the conductor is directly proportional to the voltage (Ohm's law): I=U/R The proportionality coefficient R is called electrical resistance and is measured in ohms (Ohm). The cause of electrical resistance is the presence of interference when charges move along a conductor; in solid conductors, electrical resistance arises due to the transfer of part of the energy of moving electrons to the ions of the crystal lattice.

Flowing through conductors, electric current does work and serves a person. The result of the work can be: heating of the conductor, its movement in a magnetic field, emission of electromagnetic waves, etc. How to calculate the work of electric current? The voltage at the ends of the circuit section is numerically equal to the work of the electric field to move a charge of 1 C from one point of the field to another: U=A/q ​​→ A=U*q (1) I=q /t → q=I*t (2) ; (2) substitute into (1): A=U*I*t (3) The work on a section of the circuit is equal to the product of the voltage at the ends of this section by the current and the time during which the work was done. Formula (3) can be transformed using Ohm's law.

The work done by electric current in SI is expressed in joules (J). Since the unit 1J is very small, in practice the work of electric current is measured in kW*h. Let us establish the connection between kW*h and J. 1kW*h=1000W*3600s=3600000J The work of electric current is measured in everyday life special devices- counters. Electric meter(counter electrical energy) has the symbol - Wh Created by Edison. When current passes through the meter, a light aluminum disk begins to rotate inside it. The speed of its rotation turns out to be proportional to the current and voltage. Therefore, according to the number of revolutions made by him in given time, we can judge the work done by the current during this time. Wh

Electric current power. The power of the electric current, which is designated by the letter P, is equal to the ratio of the work of the current to the time during which this work was performed. P=A/t; P=I*U The unit of electric current power is the watt (W). The following multiple power units are used: 1MW=1000000W (megawatt); 1kW=1000W (kilowatt); 1gW=100W (hectowatt). Power is measured by a wattmeter, its symbol is W

On electrical appliances that you have at home, the power and voltage are usually indicated, knowing which it is easy to calculate the current consumed by each of the devices and the electrical resistance of the device. IN residential buildings The current in the conductor should not exceed 10A. Let's calculate the maximum permissible power of electricity consumers that can simultaneously work in the apartment. At a voltage of 220V, the corresponding power is equal to: P=10A*220V=2200W=2.2kW. Simultaneous inclusion of devices with a larger total power into the network will lead to an increase in current strength and is therefore unacceptable.

Fill in the table designation name formula Unit of measurement Device for measuring AR

What instruments are needed to experimentally determine the operation of electric current? Before you are instruments: thermometer, hydrometer, voltmeter, clock, barometer, ammeter, ruler, select those that are necessary to determine the operation of electric current? Prove their necessity.

What is the name of ELECTRICAL APPLIANCE No. 1? A device for measuring the work of current (or the electricity consumed to perform this work). It is installed wherever electricity is used. Created by Edison. A very strict inspector is looking at you from the wall. He looks, doesn’t blink; As soon as you turn on the light or plug in the stove, everything goes away. Is the expression true: “Paying for light?” What are we paying for?

Exercise. Considering the power for which they are designed electrical devices in the table, answer the question: Is simultaneous switching on allowed in an apartment: Name Power kW Name Power kW Refrigerator 0.2 Electric iron 0.6 TV 0.3 Vacuum cleaner 0.65 Hair dryer 0.4 Washing machine 0,5

The power of electric lamps is 25, 60, 100 W. Which one consumes the least amount of energy at the same time? Why? Does it depend general power current on the light bulbs depending on the method of switching on, if the voltage of the current source remains unchanged, calculate it numeric value for data electrical diagrams. 6V 6V 3Ohm 3Ohm 3Ohm 3Ohm

The light was on for 1 minute. Using the data on the lamp, determine as many physical quantities as possible. The power of the electric iron is 0.6 kW. Calculate the current energy required to iron clothes for 3 hours. The family paid 56 rubles for the use of electricity 56 kopecks per 1 kWh. Determine the energy expended.

Check yourself. voltmeter ammeter clock

Homework. § 18, experimental task on page 49. When using electricity, try to save it. Remember, 36 kg of bread can be baked for 1 kWh saved

“Work and current power” - Electric current power is the work performed by the current per unit of time. Work of electric current. Learn to apply formulas when solving problems. Calculate the energy consumed (1 kWh costs 1.37 rubles). James Watt. Work and power of electric current. Sixteenth of March Cool work.

“Mechanical work and power” - Power” Develop logical thinking, skills in solving calculation problems. Watt James (1736-1819) Scottish engineer and inventor. Problem 1. A pump pumps out water with a volume of 5 cubic meters in 10 minutes. Prepared by: Nedyakina E. And physics teacher. Repeat and consolidate acquired knowledge on the topic “Mechanical work.

“Problems on electric current” - Electric current. Quiz. Second level tasks. 2. There are two lamps with a power of 60 W and 100 W, designed for a voltage of 220V. Physics lesson: generalization on the topic “Electricity”. Resistance. Purpose of the lesson: Work of current. Voltage. Current strength. Basic formulas. First level tasks. Terminological dictation.

“Electrical circuits, grade 8” - 3. Clock. 5. What are the advantages and disadvantages series circuit? 4. How to calculate the total resistance of a series electrical circuit? Parallel? Test. 1. Ammeter. What about work. Units. Q – electric charge. To measure the work of electric current, three instruments are needed: 2. Can the current strength change in different parts of the circuit?

“Electrical resistance grade 8” - Reason. Electrical resistance- R. Conductor lengths – l Sectional areas – S Substances – p. Different conductors have different resistance. - The value is constant and does not depend on either U or I. Presentation on the topic: “Electrical resistance of conductors.” Electrical resistance depends on.

Physics lesson in 8th grade.

, physics teacher, Nikitinskaya Secondary School

Subject: M electric current power.

Lesson type:combined.

Lesson objectives:reveal the concept of power of electric current, find out on what factors the power of electric current depends, reveal methods for determining power.

Tasks:

Educational:

Educational:

consolidate existing knowledge on the topic “Electric current”.

get to know the concepts

continue to develop the ability to explain processes in an electrical circuit.

formation of communicative qualities, communication culture

developing interest in the subject being studied

stimulating curiosity and activity in the classroom

development of performance

Educational:

development of cognitive interest

development of intellectual abilities

development of skills to highlight the main thing in the material being studied

development of skills to generalize studied facts and concepts

Forms of work:frontal, work in small groups, work in pairs, individual.

Means of education:

Textbook “Physics 8” A.V. Peryshkin

Collection of problems in physics for grades 7-9, A.V. Peryshkin,

Handouts (test sheets, practical tasks).

Sources of electric current.

Ammeters.

Voltmeters.

Light bulbs.

Connecting wires.

Presentation “Electric current power”.

Computer.

Illustrations on the topic.

Lesson plan:

Organizing time.

Express survey

Staging educational tasks

Collaborative exploration of the problem

Designing a new way of action.

Transition to the stage of solving particular problems

Control at the completion stage educational topic

Homework.

Educational technologies and teaching methods: ICT technology, research, problem-based teaching methods, elements of student-centered learning, differentiated learning

Used Books:

Peryshkin A.V. textbook “Physics 8”

Lukashk “Collection of problems in physics grades 7 - 9”, Moscow, “Drofa”, 2008.

V.A. Orlov “Thematic tests in physics grades 7 - 8”, Moscow, “Verbum - M”, 2001.

G.N. Stepanova, A.P. Stepanov “Collection of questions and problems in physics grades 5 - 9”, St. Petersburg, “Valeria SPD”, 2001.