Presentation on the topic of electrical work. Electrical engineering and electronics Linear DC circuits. The end result will be the cost

Energy and power in electrical circuit direct current. From the definition of EMF it follows that the work done by the source electrical energy, i.e. the work of external forces in the source for the separation of charges is equal to: From the definition of direct current it follows that the amount of charge passed through the conductor section during time t is equal to: where E - (EMF) electromotive force, IN; A is the work of external forces when moving the charge (J); q is the charge, (C). where I - electric current, (A); q is the charge, (C); t is time (s).

Combining the two previous formulas, we get the work done by the source of electrical energy in time t: On the load resistance, i.e. the receiver of electrical energy at voltage U and current I does work (energy is consumed): The units of energy are 1 joule (1 J); 1 joule is equal to 1 watt-second (1 J = 1 W s). Energy is sometimes expressed in kilowatt-hours (on electricity meters) 3.6 10 6 J = 1 kWh.

Joule Lenz's law: when a direct current flows through a conductor, electrical energy is converted into thermal energy, and the amount of heat released will be equal to the work of electrical forces: The units of measurement of the released heat are 1 joule (1 J).

Power balance The power developed by sources of electrical energy is equal to the power of converting this energy into other types of energy. This is expressed by the power balance of the electrical circuit where on the left side is the sum of the powers developed by the sources, on the right is the sum of the powers of all receivers and irreversible energy conversions inside the sources (losses due to internal resistances).

Efficiency Coefficient useful action(COP) of an electrical circuit is the ratio of the power of the receiver (useful) to the total power of all consumers. Task 2.2. Within 30 minutes, the electrical installation was connected to a 220 V DC network. A current of 4.5 A flowed in the circuit. The heater efficiency η=0.6. How much heat was released during the operation of the heater? 1) Determine the power of the electrical installation: W, 2) Determine the amount of heat: k J.

Operating modes of the electrical circuit Depending on the value of the load resistance, the electrical circuit can operate in different modes: 1. nominal (a) 2. matched (a) 3. idling (b) 4. short circuit (c) E Rin RnRn E RnRn E RнRн Ikz a) b) c)

The nominal mode is the design mode in which the circuit elements operate under conditions corresponding to the design data and parameters. The nominal values of voltages, currents and powers are indicated in the product data sheets. Rated voltages are standardized and for networks up to 1000 V are equal: 27, 110, 220, 440 V - at direct current; 40, 127, 220, 380, 660 V - with single-phase alternating current. RнRн E Rin

The rated power value for a source of electrical energy is the maximum power that the source at normal conditions work can be given to an external circuit without the danger of insulation breakdown and exceeding allowable temperature heating. The rated power value for consumers of the engine type is the power that they can develop on the shaft under normal operating conditions. RнRн E Rin

Operation in a coordinated mode for powerful circuits is not economically viable. The matched mode is used in low-power circuits, where the efficiency is not significant, but it is required to obtain more power at the load. In powerful circuits Rvn

Idling is a mode in which the electrical circuit is open and the current I in the load is 0. The voltage at the source terminals will be the largest and equal to EMF source: where Uxx - voltage at the source at idle, (V); E - source emf, (V). This mode is used to measure the EMF of a source. E Rin RnRn Uхх

A short circuit is a mode in which the outputs of the source are connected to each other by a conductor with zero resistance. The current in the circuit tends to its maximum, the voltage at the source and the load resistance are zero. where Ukz is the voltage at the source at short circuit E Rin RнRн Ikz

Internal electrical resistance ideal source voltage is 0, and internal resistance of a real voltage source should tend to 0, then the CVC of a real source will tend to CVC of an ideal source, i.e. will be load independent.

Ideal current sources and EMF are sources of infinite power. A real source of electrical energy can be represented by an equivalent circuit of an EMF or current source. This is possible on the basis of the law of conservation of energy (energy cannot arise from nothing and cannot disappear into nowhere, it can only pass from one form to another). In this case, the power Pi developed by the source is equal to the power P H given to the load and the power loss P HV inside the source. Real sources at load R H >> R H H operate in modes close to the idle mode, i.e. in modes close to the mode of an ideal EMF source. With a load resistance R N > R HV, they operate in modes close to the idle mode, i.e. in modes close to the mode of an ideal EMF source. With load resistance R N

About the direction of the current. In electrical engineering, it was generally accepted that current flows from plus to minus. Benjamin Franklin (1760) All the basic formulas and rules were formulated on the basis of this rule. After some time, an electron was discovered - a charge carrier in conductors. John Thomson (1896) The electron has a conditionally negative charge of (- 1.6 * C) and therefore, accumulating on the negative terminal of the source of electrical energy, it hurries to get to the positive terminal when the circuit is closed. Those. the movement of an electron occurs from a conditional minus to a conditional plus. Due to the fact that all the rules would have to be changed, it was decided that for the calculations they would leave the conditional positive direction of the current from plus to minus - the movement of positively charged particles.

For the positive direction of the voltage on the receivers of electrical energy, the direction coinciding with the selected positive direction of the current AC R UAСUAС I electrical voltage along the path outside the source between points A and C is called the potential difference. where U AC - potential difference between points A and C, (B); φ A is the potential of point A, (B); φ C is the potential of the point C, (B).

Ohm's Law (1827) Ohm's Law defines the relationship between current, voltage, and resistance in sections of a circuit. For each section of the circuit that does not contain sources, Ohm's law has the form: where I is the electric current, (A); U – voltage, (V); R is the resistance of the circuit section, (Ohm). The direction of the EMF of the source is indicated by an arrow inside the source, and the direction of the current in the current source is also indicated by arrows inside it. The direction of voltage U between the outputs of the EMF source is directed from + to -, i.e. opposite to the direction of the EMF.

Task 2.3. What current will flow in a circuit consisting of three batteries and external resistance R = 30 Ohm, if the EMF of each battery is E = 1.45 V, and the internal resistance R HV = 0.5 Ohm? How will the voltage U AB change when the external resistance decreases to 2 ohms? 1) We determine the current in the circuit at R \u003d 30 Ohm: A,

Task 2.3. What current will flow in a circuit consisting of three batteries and external resistance R = 30 Ohm, if the EMF of each battery is E = 1.45 V, and the internal resistance R HV = 0.5 Ohm? How will the voltage U AB change when the external resistance decreases to 2 ohms? 3) Determine the current in the circuit at R=2 Ohm: A,

Task 2.3. What current will flow in a circuit consisting of three batteries and external resistance R = 30 Ohm, if the EMF of each battery is E = 1.45 V, and the internal resistance R HV = 0.5 Ohm? How will the voltage U AB change when the external resistance decreases to 2 ohms? 4) Determine U AB: V. The voltage U AB at the load R decreased with a decrease in load resistance.

Task 2.4. What current will flow in a circuit consisting of three batteries and external resistance R = 2 Ohm, if the EMF of each battery is E = 1.45 V, and the internal resistance R HV = 0.5 Ohm, while one of the elements is connected opposite to the other two? 1) We determine the current in the circuit at R \u003d 2 Ohm: A,

From expressions (1) and (2) we can write a general expression for the current of the active section of the circuit (3) (1) (2) (3) This expression is called the generalized Ohm's law. It follows from it that the current of the active section of the circuit is equal to the algebraic sum of its voltages and EMF, divided by the resistance of the section. EMF and voltages are taken with a + sign if their directions coincide with the current direction, and with a - sign when the directions are opposite to the current direction.

Kirchhoff's Laws (1845) Kirchhoff's first law applies to the nodes of an electrical circuit. For DC circuits, it reads: the algebraic sum of the currents in the node of the electrical circuit is zero where I k is the electric current of the k branch, (A); n is the number of branches attached to the given node. Currents directed to the node (incoming) are usually taken as positive, and from the node (outgoing) - negative. The law describes the fact that at direct currents, charges do not accumulate in the node of the electrical circuit. Kirchhoff's laws (1845) Kirchhoff's second law applies to electrical circuit circuits. For DC circuits, it says: the algebraic sum of the EMF sources in any circuit of a branched electrical circuit is equal to the algebraic sum of the voltage drops across all electrical resistances of this circuit. where E s is the EMF of the s-th source, (V), I k is the electric current of the k branch, (A); R k is the electrical resistance in the k branch. m is the number of branches in the circuit, n is the number of EMF sources.

Kirchhoff's laws (1845) If the direction of the EMF coincides with the selected direction of bypassing the circuit, then such an EMF is written with a plus sign, otherwise with a minus. If the currents in the branches coincide with the selected direction of bypassing the circuit, then their product by the electrical resistance is written with a plus sign, otherwise with a minus sign. The law describes the fact that when going around the contour and returning to the starting point, the potential of the latter cannot change, since otherwise the law of conservation of energy would not be observed.

Kirchhoff's laws (1845) For the abdc circuit, Kirchhoff's second law will take the form EMF E 2 in this case is taken with a minus sign, because its direction does not coincide with the chosen direction of the circuit bypass (clockwise. On the right side of the expression, all products are taken with a plus sign, because the currents in the branches coincide with the direction of bypassing the circuit, and the product R 4 ·I 4 with a minus sign, because current I 4 does not coincide with the direction of bypassing the circuit.

Lesson topic:

Work and power electric current

1. What letter is used to denote electrical voltage?

1) I 2) U 3) R 4) q

2. What is the unit of measure for electrical resistance called?

1) Joule 2) Ampere 3) Ohm 4) Volt

3. What letter is used to denote the strength of the current?

1) A 2) I 3) V 4) R

4. Which of the following values is the same for all series-connected conductors?

1) voltage 2) current 3) resistance 4) charge

5.Sila current in the conductor:

1) is directly proportional to the voltage at the ends of the conductor and its resistance
2) inversely proportional to the voltage at the ends of the conductor and its resistance
3) is directly proportional to the voltage at the ends of the conductor and inversely proportional to its resistance
4) is directly proportional to the resistance of the conductor and inversely proportional to its resistance.

1. 2)
2. 3)
3. 2)
4. 2)
5. 3)

Work of electric current

To determine the work of an electric current in any section of the circuit, it is necessary to multiply the voltage at the ends of this section of the circuit by the electric charge that has passed through it.

A=U*q

A - Work,

U - Voltage,

q - Electric charge.

The work of an electric current is proportional to the strength of the current, voltage and time of passage of the current.

A=I*U*t

A - Electric current work,

I - Current strength,

U - Voltage,

t - Current passing time

Work of electric current

Unit of Work: Joule (J)

1 Joule = 1 Volt * 1 Amp * 1 second

1 J = 1 V * 1A * 1s

Units of work in multiples of the Joule: hectojoule, kilojoule, megajoule.

Express in Joules the work equal to

Instruments needed to measure the work of the current in the circuit:

Voltmeter

Ammeter

Power

Power is numerically equal to the work done per unit time.

P - Power

Power

Power unit: Watt (W)

1 Watt = 1 Volt * 1 Amp

1W = 1V * 1A

Units of power in multiples of watts: hectowatt, kilowatt, megawatt.

Express in watts the power equal to:

How much work is done by electric current in a light bulb in 3 minutes. Calculate the power of the electric current.

Name

Letter designation

Unit

Electric charge

Basic Formula

Current strength

Definition

Voltage

Resistance

Work of electric current

Power

Reflection

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Slides 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 / s table

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

work electric field that creates a current is called the work of the current. Voltage U is the work of electric current to move a unit electric charge: U \u003d A / q The unit of voltage is the volt (V). The voltage in the circuit section is measured with a voltmeter, its symbol in the circuits. The voltmeter is connected to the circuit in parallel with the consumer. VV

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 strength in the conductor is directly proportional to the voltage (Ohm's law): I \u003d U / R The proportionality coefficient R is called electrical resistance and is measured in ohms (Ohm). The reason for 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 the conductor, its movement in a magnetic field, radiation of electromagnetic waves, etc. How to calculate the work of an electric current? The voltage at the ends of the circuit section is numerically equal to the work of the electric field to move the charge in 1C from one point of the field to another: U=A/q → A=U*q (1) I=q /t → q=I*t (2) ; (2) let's substitute in (1) : A=U*I*t (3) The work on the section of the circuit is equal to the product of the voltage at the ends of this section and the current strength and the time during which the work was done. Formula (3) can be transformed using Ohm's law.

The work of an 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's establish a relationship between kW * h and J. 1 kW * h \u003d 1000 W * 3600 s \u003d 3600000 J special devices- counters. Electric meter(electrical energy meter) has a 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 is proportional to the current and voltage. Therefore, according to the number of revolutions made by him for 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 denoted by the letter P, is equal to the ratio of the work of the current to the time for which this work was completed. P=A/t; P=I*U The unit of electrical power is the watt (W). The following multiple units of power are used: 1MW=1000000W (megawatt); 1kW=1000W (kilowatt); 1gW=100W (hectowatt). Power is measured by a wattmeter device, its symbol W

On electrical appliances that you have at home, power and voltage are usually indicated, knowing which it is easy to calculate the current consumed by each of the devices, the electrical resistance of the device. IN residential buildings current strength in the conductor should not exceed 10A. We calculate the maximum allowable power of electricity consumers that can simultaneously work in an apartment. At a voltage of 220V, the corresponding power is equal to: P \u003d 10A * 220V \u003d 2200W \u003d 2.2 kW. Simultaneous inclusion of devices with a higher total power into the network will lead to an increase in current strength and therefore is unacceptable.

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

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

What is the name of ELECTRIC APPLIANCE #1? A device for measuring the work of current (or the electricity used to do this work) It is installed wherever electricity is used. Created by Edison. A very strict controller from the wall looks point-blank. Looks, does not blink; one has only to turn on the light Or plug the oven into the socket - everything is winding on the mustache. Is the expression "Payment for light" true? What do we pay?

Exercise. Considering the power for which they are designed electrical devices in the table, answer the question: Is it possible to switch on simultaneously in the 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

Power electric lamps 25, 60, 100W. Which of them consumes the least energy in the same time. Why? Does it depend general power current on the bulbs from the method of switching on, if the voltage of the current source remains unchanged, calculate it numerical value for data electrical circuits. 6V 6V 3Ω 3Ω 3Ω 3Ω

The lamp was on for 1 minute. Using the data on the lamp determine as many physical quantities. 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