Electrical circuits. Presentation "Electrical circuits. Elements and parameters of electrical circuits" Electrical circuits and their elements presentation

Electrical circuits. Elements and parameters of electrical circuits

physics teacher, Municipal Educational Institution “Secondary School No. 1 with UIOP”, Nadym Roschinskaya Antonina Anatolyevna

• Electrical circuit is a collection of devices and objects that form the path of electric current. A separate device that is part of an electrical circuit and performs a specific function in it is called an element of the electrical circuit.
• An electrical circuit consists of a source of electrical energy, consumers and connecting wires connecting the source of electrical energy to the consumer.

• direct current;
• alternating current;
by composition of elements:
• active circuits;
• passive circuits;
• linear circuits;
• nonlinear circuits;
by the nature of the distribution of parameters:
• with lumped parameters;
• with distributed parameters;
by number of phases (for alternating current):
• single-phase;
• multiphase (mostly three-phase).

• controls (switches, switches, contactors);
• protection (fuses, relays, etc.);
• regulation (rheostats, current and voltage stabilizers, transformers);
• control (ammeters, voltmeters, etc.)

• Types of converters:
• electromechanical (alternating and direct current generators);
• electrochemical (voltaic cells, batteries, fuel cells);
• thermoelectric (contact, semiconductor).
Receivers of electrical energy convert electrical energy into other types of energy:
• mechanical (electric motors, electromagnets);
• thermal (electric furnaces, welding machines, ...);
• light (electric lamps, spotlights);
• chemical (batteries during charging, electrolytic baths).

• Electrical circuit diagram is a graphic image of an electrical circuit containing symbols of its elements, showing the connections of these elements.
• Types of schemes: structural; functional; principled; installation room, etc.
• The schematic diagram shows the complete composition of the elements and indicates all the connections between them. This diagram gives a detailed understanding of the operating principles of the product (installation).

An electrical circuit is a system of devices that provide

passage of electric current.

A diagram is a graphical representation of an electrical circuit.

A branch is a section of a circuit along which the same current flows.

A node is a junction of three or more branches.

A circuit is a closed path passing through several branches.

An independent circuit is a circuit in which at least one branch does not belong to other circuits.

N=4 – number of nodes

M=6 – number of branches

Symbols for electrical appliances:

• Voltage (EMF) of the electrical energy source – U(B).
• Power of the electrical energy source – P (W).
• The resistance of the electrical energy receiver is R(Ohm).
• Power of the electrical energy receiver – P(W).

ELECTRICAL CIRCUITS

ELECTRICAL CIRCUITS

THANK YOU

Ohm's law. Electrical circuit. Ohm's law for a section of a circuit. Electrical circuit and electrical diagram. Our vegetable garden is on the site. Power circuits. Laws of direct current. Ohm's law for a complete circuit. Law of total current. Circular processes. Training and experimental site. Electric circuits and their elements. Basics of circuit theory. Sources and consumers of current.

Georg Simon Ohm. Ohm's law for a section of an electrical circuit. Shackled by one chain, bound by one goal. Energy flow and power circuits. Parameters of electrical circuit elements. Lesson topic: Ohm's Law. Fundamentals of the theory of electrical circuits. School training and experimental site. Application of Ohm's law to a section of a circuit. DC laws for circuit sections.

Service chains. Electric circuit and its components. Food chains and ecological pyramids. Food chains and energy flows in ecosystems. Lesson on the topic: "Electrical circuits and their elements." MEASUREMENT OF AIR FLOW PARAMETERS. Lesson topic: Ohm's law for a section of a circuit. Presentation for a physics lesson in grade 8 on the topic: “Electric circuit and its components.”

Calculation and analysis of processes in electrical circuits. Features of studying Ohm's law for a section of a circuit. Application of Ohm's law to a section of a circuit when solving problems. Calculation of complex DC circuits using Kirchhoff's I and II laws. Stages of establishing the Orenburg section of the Russian-Kazakh border. Methodological and practical aspects of the application of Law No. 44-FZ (on the contract system).

General physical training through circuit training in a volleyball lesson in 8th grade. In total, 25 deposits and areas of sand and gravel material, 60 peat deposits and 2 sapropel deposits have been identified and explored on the territory of the Kuvshinovsky district.

1 DC electrical circuits 1.1 Elements of DC electrical circuits Electrical diagrams are drawings that show how electrical devices are connected in a circuit. An electrical circuit is a set of devices designed for the transmission, distribution and mutual conversion of energy. The main elements of an electrical circuit are sources and receivers of electrical energy, which are connected to each other by conductors. In sources of electrical energy, chemical, mechanical, thermal energy or other types of energy are converted into electrical energy. In electrical energy receivers, electrical energy is converted into thermal, light, mechanical and others. Electrical circuits in which energy production, transmission and transformation occur at constant currents and voltages are called direct current circuits.

An electrical circuit consists of individual devices or elements, which, according to their purpose, can be divided into 3 groups. The first group consists of elements intended for generating electricity (power supplies). The second group is elements that convert electricity into other types of energy (mechanical, thermal, light, chemical, etc.). The third group includes elements designed to transmit electricity from a power source to an electrical receiver (wires, devices that ensure the level and quality of voltage, etc.).

1.2 Energy sources EMF sources An EMF source is characterized by an EMF value equal to the voltage (potential difference) at the terminals in the absence of current through the source. EMF is defined as the work of external forces inherent in the source to move a single positive charge inside the source from a terminal with a lower potential to a terminal with a higher potential. Figure Designation of EMF source and galvanic element in circuits

DC circuit power sources are galvanic cells, electric batteries, electromechanical generators, thermoelectric generators, photocells, etc. All power sources have internal resistance, the value of which is small compared to the resistance of other elements of the electrical circuit. DC power receivers are electric motors that convert electrical energy into mechanical, heating and lighting etc. All electrical receivers are characterized by electrical parameters, among which are the most basic voltage and power. For normal operation of the electrical receiver, it is necessary to maintain the rated voltage at its terminals. For DC receivers it is 27, 110, 220, 440 V, as well as 6, 12, 24, 36 V.

The terminal voltage of a real source depends on the current through the source. If this dependence can be neglected, then such a source is called ideal. On the design diagrams it is necessary to indicate the directions of voltages and currents (selected arbitrarily). Figure Scheme with a real EMF source

For real sources, let's write Ohm's law for a complete circuit: U= I ·R n (1.1) where I - current [A], E - emf [B], R - resistance [Ohm]. It follows: U=E-I×R BH (1.2) The voltage U at the terminals of a real source is less than the EMF by the amount of the voltage drop across the internal resistance. An ideal source has R in =0. The maximum current occurs in short circuit mode at R n =0, while the output voltage U also tends to zero.

1.2.2 Current source The current source is characterized by current I with short-circuited terminals (in the absence of voltage). If the current does not depend on voltage, such a source is called ideal. Figure Image of a current source in circuits

The current I of a real energy source depends on the voltage U at its terminals. From Ohm's law for a complete circuit: (1.3) where is the conductivity [Sm]. Figure Circuit with a real current source In this circuit, the element g in parallel connected to an ideal source J is called internal conductivity. An ideal current source has g in = 0 (that is, R in =).

1.2.3 Electric power Characterizes the energy generated by the source per unit time. For a real voltage source: P=E × I [W] (1.4) For a real current source: [W] (1.5) Load resistance Rn characterizes the consumption of electrical energy, that is, its conversion into other types at a power determined by the formula: [W] (1.6)

1.3 Generalized Ohm's law for a section of a circuit with EMF - direction from a point with a high potential to a point with a lower potential; - direction of current. Figure Unbranched circuit with EMF sources

(1.7) where: - total resistance of the circuit section; - voltage between the terminals of the section under consideration; - algebraic sum of the EMF acting in a given area. If the EMF coincides in direction with the current, then a sign is placed, if it does not coincide -. Conclusion: the current of a section of a circuit with EMF sources is equal to the algebraic sum of its voltage and EMF, divided by the resistance of the section.

1.4 The simplest transformations in electrical circuits Series connection of resistances The current flowing in the circuit is the same at any point. Figure Equivalent resistance when resistors are connected in series

1.4.2 Parallel connection of resistances Figure Parallel connection of resistances

For the equivalent resistance, we write the formula: (1.11) The equivalent resistance of a circuit consisting of parallel components is always less than the smaller resistance of the circuit. Therefore, with a parallel connection, the equivalent conductance of the circuit is equal to the sum of the conductances of the individual branches.

1.4.3 Replacing a current source with an EMF source Figure Replacing a current source with an EMF source The power balance is different in these circuits because different current flows through the resistance R. The result of solving a problem must always be reduced to the original diagram. For a circuit with a current source, the following relationship is valid: J - I total - I R =0 (1.12)

1.5 Connecting measuring instruments to electrical circuits Before making measurements in electrical circuits, you need to decide on the following questions, based on the answer to which, you select a measuring device: - permanent or alternating current present in this electrical circuit. If variable, then which one (signal shape, frequency); - what order of currents and voltages are there in this circuit; -what measurement error will satisfy us.

1.5.1 Voltage measurement To measure the voltage drop on any section of the circuit, connect a voltmeter in parallel to it, taking into account the polarity. The voltmeter has some internal resistance R v, therefore, during operation, part of the current from the electrical circuit will flow through the voltmeter, thereby changing the mode of the electrical circuit when the voltmeter is connected. This means that the measurement result will contain an error. Figure Measuring the voltage drop across R 2 with a voltmeter

Voltage on R 2, a circuit consisting of a source and series-connected resistances R 1 and R 2 without a voltmeter: (1.13) where R ext is the internal resistance of the source. Voltage on R 2, a circuit consisting of a source and series-connected resistances R 1 and R 2 with a voltmeter: (1.14) If, then In order for the voltmeter not to affect the circuit under study, they try to make the internal resistance of the voltmeter as large as possible.

1.5.2 Measuring currents To measure the amount of current flowing through a certain element of the circuit, an ammeter is connected in series with it in the open branch, taking into account the polarity. Since the ammeter has some resistance R A, its inclusion in an electrical circuit changes its mode, and the measurement result contains an error. Figure Measuring current with an ammeter

Current strength in a circuit consisting of a source and series-connected resistances R 1 and R 2 without an ammeter: (1.15) where R ext is the internal resistance of the source. Current strength in a circuit consisting of a source and series-connected resistances R1 and R2 with an ammeter: (1.16) Where R ext is the internal resistance of the source; R A - ammeter resistance. To reduce errors, they try to make the resistance of ammeters as small as possible.

1.5.3 Measuring Power To measure the power consumed by any circuit element, it is necessary for the meter to measure the voltage drop across it and the current through it and multiply these values. Wattmeters have four input terminals - two for current and two for voltage. Figure: Circuit diagram for connecting a wattmeter to measure the power consumed by R 2.

1.5.4 Bridge circuits Bridge circuits are used to measure resistance. ac, cb, ad, bd - bridge arms. ab, cd - diagonals of the bridge. Drawing of Wheatstone Bridge

To measure resistance with a balanced bridge, an unknown resistance is included in one of its arms. By adjusting any of the other arms, using known resistances, the balance of the bridge is achieved (i.e. when the voltmeter shows zero). After this, unknown resistance is found. For powering the bridge, the value of EMF E is not significant. It is important that there is no noticeable heating of the resistances, and that the sensitivity of the voltmeter is sufficient. The resistance of the measuring device also does not matter, because in a balanced state, the potential difference between points c and d is zero, therefore, no current flows through the voltmeter. Unbalanced bridges are also used, in which the arms are not adjusted, and the value of the unknown resistance is calculated according to the readings of a measuring device with a specially calibrated scale. When measuring with an unbalanced bridge, it is necessary to stabilize the EMF E. (1.45)

1.5.5 Compensation measurement method The EMF value is measured using potentiometers. The potentiometer is designed in such a way that when measuring the EMF value E x, there is no input current. Figure Potentiometer

Before work, the device is calibrated: to do this, turn the switch to position. Using R I, the operating current in the circuit is adjusted so that the voltage drop across the resistance R is equal to the value of the EMF of a normal NE element. In this case, the voltmeter should show zero. To measure the EMF E X, the switch is moved to position, using the calibrated slider slider R p, the voltmeter shows zero, and the readings of the device are read.

1. The concept of “Electrical circuit” 2. The main elements of an electrical circuit 3. What is commonly called “DC circuits”? 4.How is the “EMF source” characterized? 5.What does the voltage at the terminals of a real source depend on? 6.How is the “current source” characterized? 7. From Ohm's law for a complete circuit. 8.Calculation determination of conductivity. 9.What characterizes “Electric power”? 10. Generalized Ohm's law for a section of a circuit with an EMF. 11.Series connection of resistances. 12.Parallel connection of resistances. 13.Replacement of a current source with an EMF source, characteristics. 14.Connecting measuring instruments to electrical circuits. 15.Measurement of voltages, methodology. 16.Measurement of currents, technique. 17. Power measurement, methodology. 18.Bridge circuits 19.Compensation method of measurement CHECK QUESTIONS Notes, additions The section of an electrical circuit along which the same current flows is called a branch. The junction of the branches of an electrical circuit is called a node. On electrical diagrams, a node is indicated by a dot. Any closed path passing through several branches is called an electrical circuit. The simplest electrical circuit has a single circuit; complex electrical circuits have several circuits. Matched mode between the power supply and the external circuit occurs when the resistance of the external circuit is equal to the internal resistance. In this case, the current in the circuit is 2 times less than the short circuit current. The most common and simplest types of connections in an electrical circuit are series and parallel connections.

The elements of an electrical circuit are various electrical devices that can operate in various modes. The operating modes of both individual elements and the entire electrical circuit are characterized by current and voltage values. Since current and voltage can generally take on any values, there can be an infinite number of modes. Idle mode is a mode in which there is no current in the circuit. This situation can occur when the circuit breaks. The nominal mode occurs when the power source or any other circuit element operates at the values ​​of current, voltage and power specified in the passport of this electrical device. These values ​​correspond to the most optimal operating conditions of the device in terms of efficiency, reliability, durability, etc. Short circuit mode is a mode when the receiver resistance is zero, which corresponds to the connection of the positive and negative terminals of the power source with zero resistance. The short circuit current can reach large values, many times higher than the rated current. Therefore, short circuit mode is an emergency for most electrical installations.

References Main 1. Fundamentals of circuit theory. G. V. Zeveke, P. A. Ionkin, A. V. Netushil, S. V. Strakhov. M.: Energoatomizdat, 1989, 528 p. 2.Theoretical foundations of electrical engineering. Volume 1. L. R. Neiman, K. S. Dimirchyan L.: Energoizdat, 1981, 536 p. 3.Theoretical foundations of electrical engineering. Volume 2. L. R. Neiman, K. S. Dimirchyan L.: Energoizdat, 1981, 416 p. 4.Theoretical foundations of electrical engineering. Electrical circuits. L. A. Bessonov M.: Higher. school, 1996, 638 p. Additional 1. Fundamentals of the theory of electrical circuits. Tatur T. A. Higher school, 1980, 271 p. Collection of tasks and exercises on the theoretical foundations of electrical engineering. /Ed. P. A. Ionkina. M.: Energoizdat, 1982, 768s Guide to laboratory work on the theory of linear circuits of direct and sinusoidal current. /Ed. V. D. Eskova - Tomsk: TPU, 1996, 32 pp. Guide to laboratory work on steady-state modes of nonlinear circuits and transient processes in linear circuits. /Ed. V. D. Eskova - Tomsk: TPU, 1997, 32 p.

1 slide

2 slide

Qualitative problems Will the readings of the ammeter and voltmeter change if the rheostat slider is moved in the direction of the arrow? 1. First of all, in this type of task it is important to understand that the voltage at the terminals is constant. If a current source (for example, a battery) was drawn on the diagram, then this condition would not be met! Be careful! 2. When you move the rheostat slider to the left, the resistance of the rheostat becomes less - the current flows only along the left side of the rheostat, it becomes shorter. This means that the resistance of the entire circuit also becomes less, because The rheostat and resistor are connected in series. 4. The voltmeter shows the voltage across the resistor. Because If the current is the same throughout the circuit, more current will flow through the resistor. This means the voltage on it will increase: U=I.R. The voltmeter will show an increase in voltage.

3 slide

Qualitative problems Will the voltmeter reading change if the rheostat slider is moved in the direction indicated by the arrow? The voltage at the circuit terminals is maintained constant. Solve the problem yourself. Check the answer by clicking on this text Voltage will not change

4 slide

Calculating the total resistance of the circuit Calculate the total resistance of the circuit shown in the figure ATTENTION! In such problems it is convenient to use the equivalent circuit method. When we are looking for the “total” resistance of a section of a circuit, we are looking for the resistance of a resistor whose effect in this circuit would be the same. That is, the resistance of one resistor would be equivalent to the resistance of the whole section Values: R1=R2=R3=15 Ohm R4=25 Ohm R5=R6=40 Ohm

5 slide

Calculation of the total resistance of the circuit Consider the first section of the circuit. All resistors on it are connected in parallel and equal to each other. This means, using the laws of parallel connection, we find the total (equivalent) resistance of the section: Now we can draw an equivalent circuit, replacing the entire first section with a resistor with resistance RI

6 slide

Calculation of the total resistance of the circuit Consider the third section of the circuit. All resistors on it are connected in parallel and equal to each other. This means, using the laws of parallel connection, we find the total (equivalent) resistance of the section: Now we can draw an equivalent circuit, replacing the entire first section with a resistor with resistance RII

7 slide

Calculating the total resistance of a circuit Now the circuit has been converted into a simple circuit in which there are only three sections connected in series. This means, using the laws of series connection, we find the total (equivalent) resistance of the entire circuit: Answer: the total resistance of the entire circuit is 50 Ohms

8 slide

Task for independent decision Calculate the resistance of the first section RI. Check the result by clicking on this inscription RI=6 Ohm

Slide 9

Problem for independent solution Calculate the resistance of the second section RII. Check the result by clicking on this inscription RI=6 Ohm RII=2 Ohm

10 slide

Problem for independent solution Calculate the resistance of the second third RIII. Check the result by clicking on this inscription RI=6 Ohm RII=2 Ohm RIII=4 Ohm

11 slide

Problem for independent solution Calculate the resistance of the second fourth section of RIV. Check the result by clicking on this inscription RI=6 Ohm RII=2 Ohm RIII=4 Ohm RIV=2 Ohm

Slide 14

Calculation of an electrical circuit Let's use the results of resistance calculations. Because the total resistance of the circuit is 4 Ohms, then such currents flow in resistors 1 and 4, therefore, you can find out the voltages across them: U1=U4=15V. Then the voltage across resistor 7 is: U7=U-U4-U1 =30V, and the current I7=7.5A. The same voltage will be across the entire section, which we called RIII, whose resistance is 4 ohms. This means that a current also flows through resistors 2 and 5 equal to I2= I5= 7.5A I=15A, U=60V U1=U4=15V I1=I4=15A I7=7.5A, U7=30V I2= I5= 7.5A U2= U5= 7.5V Do the same reasoning yourself for the remaining sections and make sure that a current of 2.5 A flows through resistors 3, 6 and 9, and 5 A through the resistor 8. The voltage across the resistor is 8 – 15 V, on resistors 3 and 6 - 2.5 V and on resistor 9 - 10 V.

Municipal budgetary educational institution "Kordonskaya secondary school"

Electrical circuits

WITH: technology teacher

Kudinov A. A.

Cordon 2018

The simplest electrical circuit may contain only three elements:

source, load and connecting wires.

Electrical circuit -

a set of devices, elements designed for the flow of electric current, electromagnetic processes in which can be described using the concepts of current and voltage.

When assembling electrical circuits, the electrician is guided by

electrical circuit diagram .

Schematic diagram, electrical circuit diagram - a graphic image (model) used to convey, using conventional graphic and alphanumeric symbols (pictograms), connections between the elements of an electrical device.

Schematic diagram, as opposed to wiring printed circuit board does not show the relative (physical) arrangement of the elements, but only indicates which pins of real elements (for example, microcircuits) are connected to which.

Let's look at some graphic symbols on circuit diagrams

Galvanic

element

Galvanic battery

elements

Intersection

wires

Compound

wires

node

Button

switch

Resistor

(resistance)

Fuse

Electric lamp

incandescent

Electric

call

Coil

wire

Coil

with iron core

Capacitor

constant capacity

Learning new educational material

Capacitor

variable capacity

Learning new educational material

Capacitor

electrolytic

Ammeter

Voltmeter

Electrical circuit diagrams are graphic documents.

Symbols and rules for the execution of electrical circuits are determined by the state standard, which all engineers and technicians are required to comply with.

The connection lines between the elements of the circuit are drawn parallel or mutually perpendicular, observing

closed circuit condition, inclined lines do not apply.

Let's draw in a notebook a table from the textbook (p. 49), which shows the symbols of some elements of the electrical circuit.

Wiring diagrams - these are drawings showing the actual location of components both inside and outside the object shown on the diagram. Designed primarily to enable the production of an object. Takes into account the arrangement of circuit components and electrical connections(electrical wires and cables). Only general requirements for the preparation of design documentation apply.

What is an electrical circuit?

- What is a schematic diagram?

- What is a wiring diagram?

What can be classified as elements of an electrical circuit?

- depict schematic diagram electrical wiring of a house or apartment.

Homework assignment

- study paragraph 9 of the textbook;

- answer questions 1-2 on page 50 of the textbook.

Express in one sentence, choosing the beginning of the phrase:

Today I found out...

It was interesting…

It was difficult…

I completed tasks...

I understand that…

Now I can…

I purchased...

I learned (learned)…

I managed…

I was able (was able)…

I will try…

I was surprised...