Class: 8

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Lesson type: a lesson in learning new material and primary consolidation.

Target: to study the components of the electrical circuit, the symbols used in the diagrams.

Tasks:

• educational- provide perception, comprehension and primary consolidation constituent parts electrical circuit, their purpose and symbols.
• Educational- to promote the inculcation of compliance with safety regulations when assembling a chain, interest in physics.
• Educational- to promote the development of the ability to assemble electrical circuits, depict diagrams electrical circuits.

Lesson plan.

1. Organizational moment (1 min.)
2. Knowledge update. (8 min.)
3. Learning new material. (12 min)
4. Consolidation of knowledge. (15 minutes.)
5. The stage of primary knowledge testing. (5 minutes.)
6. Homework. (1 minute.)
7. Summary of the lesson. (1 minute.)
8. Reflection. (2 minutes.)

Equipment: galvanic cell, light bulb, key, connecting wires, plates with symbols of EC elements, control table, computer, multimedia projector.

During the classes

1. Org. Moment (explain group work)

Electricity all around
The plant and the house are full of them.
Life is drastically made easier!
It's amazing,
For our benefit,
All wires Majesty
It's called electricity!

2. Actualization of knowledge.

Each group is invited to choose a sheet with the question:

• What is electric current?
• What conditions are necessary for the existence of an electric current?
• Why is electricity needed?
• Direction of electric current?

(In order to prepare students for the GIA, it is necessary to include various tasks in various stages of the lesson and homework that will contribute to the formation of methodological knowledge and skills - a task with a choice of answers, the level of experimental skills, the ability to solve a qualitative problem, as well as tasks for working with the text of a physical content.)

When repeating the material, students are offered the following task: (slide 2)

3 . Using the letters in the lines, enter the names of the current sources:

slide 3

4. Learning new material.

Lesson topic:"Electrical circuit".

Open your notebooks and write down the topic of the lesson. The set of devices through which electric current flows is called electrical circuit. Chains are simple (as in a demonstration) and complex (wiring), but in all it is possible to distinguish components. Devices that use electrical energy are called consumers. This is the first part of the chain. Give examples of consumers… in the classroom… at home… on the table… (for L. R. light bulb). The second component of the circuit is a current source (for L.R. - a galvanic cell). The current source is connected to the circuit last with the help of connecting wires - this is the third component of the circuit. There is another important part of the electrical circuit. In Paris in 1881, at an electrical exhibition, everyone was delighted with this invention. This is a switch. Its role is to close and open the electrical circuit. In technology, different types of closing and opening devices are used. In order for there to be current in the circuit, it must be closed, i.e. consist of conductors of electricity. If at any point the wire breaks, then the current in the circuit will stop. This is what switches work on. Name the locking devices in the class (Switch, knife switch, buttons, for l.r. - key) slide 4.

Please note: the circuit is assembled with the switch open; the switch is made of conductors of electricity, and you need to touch the insulating handle.

So, what are the components of an electrical circuit? Write in your notebook:

• consumer
• current source
• connecting wires
• closing device

You have a page of G.N. Stepanova, the peculiarity of the textbook is that each paragraph contains keyword, in the first, for example, "Electric circuit", we will place it in the center. In the rest, the components of the chain blocks. In the margins, what is included in the blocks and as indicated on the diagram. On the table for each group is a netbook, on the desktop is a file with the word cluster. We open it and make a cluster using the tutorial.

Electrical circuits can be complex. The TV is out of order, and you need information about what the electrical circuit consists of, and the information is contained in electrical diagrams. Electrical diagrams are drawings that show how to connect the elements of an electrical circuit.

Guys, you have to do practical work.

What safety rules will you follow?

Practical work.

Target: assemble an electrical circuit from the devices that everyone has on the tables so that the light bulb lights up.

A simple circuit is assembled in groups (power source, lamp, key, connecting wires)

Completing of the work. Drawing up a diagram. The teacher checks.

5. Stage of primary testing of knowledge.

Individual tasks: arrange the cond. designations by "places", connecting with an arrow conditional. symbol with the name of the device.

Let's check using control table:

slide 1

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

slide 2

Schema types

The circuit diagram is graphic image electrical circuit, containing the symbols of its elements, showing the connections of these elements. Types of schemes: structural (block diagram); functional; fundamental; assembly, etc. Functional, in comparison with structural, reveals in more detail the functions of individual elements and devices.

slide 3


On the circuit diagram the full composition of the elements is given and all the relationships between them are indicated. This diagram gives a detailed idea of ​​how the product (installation) works. Wiring diagrams are drawings showing the actual location of the components both inside and outside the object depicted in the diagram.

slide 4

Symbols for electrical appliances

• slide 5

  The simplest electrical circuit

  Basic elements of electrical circuits: Resistance Inductance Capacitance Voltage source Current source. The main elements of the simplest electrical circuit: 1 - a source of electrical energy; 2 - receivers of electrical energy; 3 - connecting wires  1 2 3

  slide 6

  Source E.D.S

  It is such an idealized power supply voltage, on the terminals of which is constant (does not depend on the magnitude of the current I) and is equal to E.M.S. E, and the internal resistance is zero. I =0 c 0 E U

  Slide 7

  Current source

  It is an idealized power source that gives a current I=Ik, independent of the resistance of the load to which it is connected, and the E.D.S. its Eit and internal resistance Rit are equal to infinity. I =900 Ik=Eit/Rit 0 U

  Slide 8

  Auxiliary elements

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

  Slide 9

  Kirchhoff's first law

  In the branches that form the node of the electrical circuit, the algebraic sum of the currents is zero. The sum of the currents directed to the node of the electric circuit is equal to the sum of the currents directed from this node. I1 + I 2 + I 3 +... + I n = 0 This law follows from the principle of current continuity. If we assume that the currents of the same direction prevail in the node, then the charge of the same sign should accumulate, and the potential of the nodal point should continuously change, which is not observed in real circuits.

  Slide 10

  Kirchhoff's second law

  We go around the contour in an arbitrary direction, for example, clockwise. If the directions of the E.D.S. and currents coincide with the direction of bypassing the circuit, then E.D.S. (E) and voltage drops (U \u003d I * R) are taken with a plus sign, if they do not match - with a minus sign: E 1 -E 2 + E 3 \u003d U1 + U2 + U3 + U4 E3 R1 R2 R3 R4 E1 E2 I2 I3 I4 I1 In any closed circuit, the algebraic sum of the electromotive forces is equal to the algebraic sum of the voltage drops

  slide 11
  

  under the chains direct current imply circuits in which the current does not change its direction, i.e. the polarity of the sources of E.D.S. in which is constant.

  Applications for DC systems (stationary batteries) Energy (power plants, substations, power supply systems) Telecommunications systems Mobile communications Uninterruptible power systems Backup power for emergency lighting systems Solar energy storage Power systems that meet increased safety requirements (for example, public and medical institutions) Computing centers Automation systems for production and technological processes Power supplies for sea-based facilities

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1 slide

2 slide

Qualitative tasks Will the readings of the ammeter and voltmeter change if the slider of the rheostat is moved in the direction of the arrow? 1. First of all, in this kind of tasks, it is important to understand that the voltage at the terminals is constant. If a current source (for example, a battery) were drawn on the diagram, then this condition would not be met! Be careful! 2. When moving the slider of the rheostat to the left, the resistance of the rheostat becomes smaller - the current flows only through the left side of the rheostat, it becomes shorter. This means that the resistance of the entire circuit also becomes less, because. 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 that the voltage on it will increase: U=I.R. The voltmeter will show an increase in voltage.

3 slide

Qualitative tasks Will the reading of the voltmeter also change, if the slider of the rheostat is moved in the direction indicated by the arrow? The voltage at the circuit terminals is kept constant. Solve the problem yourself. Check the answer by clicking on this inscription Voltage will not change

4 slide

Calculation of 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 method of equivalent circuits. When we are looking for the "total" resistance of a circuit section, we are looking for the resistance of a resistor whose action in this circuit would be the same. That is, the resistance of one resistor would be equivalent to the resistance of the entire 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. On it, all the resistors are connected in parallel and are equal to each other. So, using the patterns of parallel connection, we find the total (equivalent) resistance of the section: Now you 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. On it, all the resistors are connected in parallel and are equal to each other. So, using the patterns of parallel connection, we find the total (equivalent) resistance of the section: Now you can draw an equivalent circuit, replacing the entire first section with a resistor with resistance RII

7 slide

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

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

9 slide

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

14 slide

Calculation of the electrical circuit Let's use the results of the calculation of resistances. Because the impedance of the circuit is 4 ohms, then such currents flow in resistors 1 and 4, therefore, you can find out the voltages on them: U1=U4=15V. Then the voltage across the resistor 7 is: U7=U-U4-U1=30V, and the current I7=7.5A. The same voltage will be on the entire section, which we called RIII, the resistance of which 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 for the rest of the sections yourself and make sure that 2.5 A flows through resistors 3, 6 and 9, and 8 - 5 A through the resistor. The voltage across the resistor is 8 - 15 V, on resistors 3 and 6 - 2.5 V and on a resistor 9 - 10 V.

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Slides captions:

Electric circuit and its components Grishina L.A., teacher of physics MKS (K) Educational Institution S (K) School 37 I II type Novosibirsk

ELECTRIC CIRCUITS In order to create an electric current, it is necessary to make a closed electrical circuit from electrical devices.

The simplest electrical circuit consists of: 1. current source; 2. electricity consumer (lamp, electric stove, electric motor, electric boiler, household appliances); 3. closing and opening device (switch, button, key, knife switch); 4. connecting wires.

Electrical circuit The simplest electrical circuit, which consists of a galvanic cell, a lamp and a key.

Wiring Diagram Drawings that show how electrical devices are connected in a circuit are called wiring diagrams.

Conventions On electrical diagrams, all elements of the electrical circuit have symbols.

1 - galvanic cell. 2 - battery of cells 3 - connection of wires 4 - intersection of wires in the diagram without connection 5 - clamps for connection 6 - key 7 - electric lamp 8 - electric bell 9 - resistor (or otherwise resistance) 10- heating element 11 - fuse

RHEOSTAT There are resistances, the value of which can be smoothly changed. It can be variable resistors or resistors called rheostats.

Symbol of a rheostat With the help of a movable slider 2, it is possible to increase or decrease the resistance value (between contacts 1 and 2) included in the electrical circuit.

Interesting! German professor G.K. Lichtenberg from Göttengen was the first to propose the introduction of electrical symbols, substantiated them practical use and used in my work! Thanks to him, mathematical plus and minus signs appear in electrical engineering to denote electric charges.

Homework §33, exercise 13, p.79

Literature Peryshkin A. V. Physics. 8th grade: Textbook for general educational institutions / A. V. Peryshkin, E. M. Gutnik - M .: Bustard, 2012 http:// fizika-class.narod.ru / Pictures from the pages of free access to the Internet

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