Lesson 57 Topic: Electric field. Electric field strength. Principle of field superposition Target: disclosure of the material nature of the electric field and the formation of the concept of electric field strength
Lesson objectives: familiarize students with the power characteristics of the electric field;
∙ to form informal knowledge in the interpretation of the concept of “electric field strength;
∙ cultivate a conscious attitude to learning and interest in studying physics.
Lesson: learning new material Equipment: light metal sleeve made of foil, plexiglass stick, plumes on a stand, electrophore machine, ball on a silk thread, capacitor plates, presentation, flash animation Lesson progress
- Repetition of what has been learned
- Formulate Coulomb's law. What is the physical meaning of the coefficient k? Determine the limits of applicability of Coulomb's law?
- Physical dictation. Law of conservation of electric charge. Coulomb's law. (mutual verification)
Learning new material
- Learning new material
- E.P. tension
Tension E.P. does not depend on the magnitude of the charge, a vector quantity (force characteristic of the field) It shows with what force the field acts on a charge placed in this field. 
Substituting the expression for force into the formula, we obtain the expression for the field strength of a point charge
How can you characterize a field created by several charges? We must use the vector addition of the forces acting on the charge introduced into the field and obtain the resulting E.P. intensity. This case is called the SUPERPOSITION PRINCIPLE( slide 6)Experiment 4. Experiments on demonstrating the spectra of electric fields. (1. Experiments with sultans installed on insulating stands and charged from an electric foil machine. 2. Experiments with capacitor plates to which paper strips are glued at one end.) It is convenient to depict the electric field with graphic lines - POWER LINES. FIELD LINES are lines indicating the direction of the force acting in this field on a positively charged particle placed in it ( slides 9,10,11)
Field lines created by positively (a) and negatively (b) charged particles 
The most interesting case is E.P. created between two long charged plates. Then a homogeneous E.P. is created between them. + - 1 2 3Explanation of the principle of superposition, using a graphical representation ( slides11,12,13)
III.Consolidation of knowledge, abilities, skills
Review questions
∙ Analysis of questions:
a) How should we understand that an electric field exists at a given point?
b) How should we understand that the tension at point A is greater than the tension at point B?
c) How should we understand that the intensity at a given point in the field is 6 N/kl?
d) What value can be determined if the strength at a given point in the field is known?
∙ 2. Analysis of qualitative problems
800. Two charges of equal magnitude are located at some distance from each other. In what case is the tension at a point lying half the distance between them greater: if these charges are like or unlike?? (Dissimilar. With point charges of the same name, the tension will be zero.)
801. Why do birds fly off high voltage wires when the current is turned on? (When a high voltage current is turned on, a static electric charge appears on the bird’s feathers, as a result of which the bird’s feathers bristle and diverge (like the tassels of a paper plume connected to an electrostatic machine). This frightens the bird, it flies off the wire.)
∙ Analysis of calculation problems [Rymkevich A.P. Collection of problems in physics, grades 10-11. – M.: Bustard, 2003.]:
698. At some point in the field, a force of 0.4 μN acts on a charge of 2 nC. Find the field strength at this point. (200 V/m)
699. What force acts on a 12 nC charge placed at a point where the electric field strength is 2 kN/Cl? (24 µN)
Summing up the lesson.
Literature:
Textbook Physics 10, B. Krongar, V. Kem, N. Koyshibaev, publishing house "Mektep" 2010
[Tulchinsky M.E. Qualitative problems in physics in high school. – M.: Education, 1972.]:
Rymkevich A.P. Collection of problems in physics, grades 10-11. – M.: Bustard, 2003
V.A.Volkov. To help the school teacher.
Subject : Electric field. Electric field strength. Principle of field superposition
The purpose of the lesson: continue the formation of the concept of “electric field”, introduce its main characteristic; study the principle of superposition of electric fields.
During the classes:
1.Organizing moment. Setting the goals and objectives of the lesson.
2.Knowledge test:
Physical dictation
Electrification of bodies. Law of conservation of charge. Coulomb's law
What is the name of the branch of physics that studies stationary charged bodies? /electrostatics/
What interaction exists between charged bodies and particles? /electromagnetic/
What physical quantity determines the electromagnetic interaction? /electric charge/
Does the magnitude of the charge depend on the choice of reference frame? /No/
Can we say that the charge of a system consists of the charges of the bodies included in the system? /Can/
What is the name of the process that leads to the appearance of electrical charges on bodies? /Electrification/
If a body is electrically neutral, does this mean that it contains no electrical charges? /No/
Is it true that in a closed system the algebraic sum of the charges of all bodies in the system remains constant? /Yes/
If the number of charged particles in a closed system has decreased, does this mean that the charge of the entire system has also decreased? /No/
Do we create an electric charge when electrifying? /No/
Can a charge exist independently of a particle? /No/
A body whose total positive charge of particles is equal to the total negative charge of particles is... /Neutral/
How will the force of interaction between charged particles change as the charge of any of these particles increases? /Will increase/
How will the interaction force change when charges move into the medium? /Will decrease/
How will the interaction force change as the distance between charges increases by 3 times? /Will decrease by 9 times/
What is the name of the quantity that characterizes the electrical properties of a medium? /Dielectric constant of the medium/
In what units is electric charge measured? /In pendants/
3.Learning new material
Electric field
The interaction of charges according to Coulomb's law is an experimentally established fact. However, it does not reveal the physical picture of the interaction process itself. And it does not answer the question of how the action of one charge on another occurs.
Faraday gave the following explanation: There is always an electric field around every electric charge. An electric field is a material object that is continuous in space and capable of acting on other electric charges. The interaction of electric charges is the result of the action of the field of charged bodies.
Electric field is a field created by stationary electric charges.
An electric field can be detected if a test (positive) charge is introduced into a given point.
A test point charge is a charge that does not distort the field under study (does not cause a redistribution of charges creating the field).
Electric field properties:
Acts on charges with some force.
The electric field created by a stationary charge, i.e. electrostatic does not change over time.
An electric field is a special type of matter, the movement of which does not obey Newton’s laws of mechanics. This type of matter has its own laws, properties that cannot be confused with anything else in the world around us.
Electric field strength
Physical quantity equal to the ratio of the force with which the electric field acts on the test chargeq, to the value of this charge is calledelectric field strength
and is designated 
:
.
The unit of tension is 1N/C or 1V/m.
The electric field and Coulomb force intensity vectors are co-directed.
An electric field whose strength is the same at all points in space is called uniform.
Lines of tension (field lines) – lines whose tangents at each point coincide with the direction of the vector .
In order to use tension lines to characterize not only the direction, but also the intensity value of the electrostatic field, they are drawn with a certain density: the number of tension lines penetrating a unit surface area perpendicular to the tension lines must be equal to the vector modulus .
If the field is created by a point charge, then the intensity lines are radial straight lines emerging from the charge, if it positive, and included in it, if the charge negative.
Principle of field superposition
Experience shows that if an electric charge q electric fields of several sources act simultaneously, then the resulting force turns out to be equal to the sum acting from each field separately.
Electric fields obey the superposition principle:
The strength of the resulting field created by the system of charges is equal to the geometric sum of the field strengths created at a given point by each of the charges separately:
or 
4. Fixing the material
Solving problems from the collection. problems ed. Rymkevich No. 696,697,698
Homework: §92,93,94
Item: PhysicsUnified State Exam discipline section: _________ _
Total lessons in the topic –_18___
№ lesson from this topic _4____
Lesson topic « Electricity. Current strength »
Lesson summary provided
FULL NAME. _ __ Bryleva Liliya Zakirzyanovna_
Academic title, position: Physics teacher
Place of work: Municipal educational institution secondary school No. 6
Physics lesson notes
"Electricity. Current strength."
Lesson objectives:
Educational - give the concept of electric current and find out the conditions under which it occurs. Enter the quantities characterizing the electric current.
Developmental - to form intellectual skills to analyze and compare the results of experiments; activate students’ thinking and ability to draw their own conclusions.
educational - development of cognitive interest in the subject, broadening the horizons of students, showing the possibility of using the knowledge gained in lessons in life situations.
Lesson type: lesson on learning new knowledge.
Equipment: presentation on the topic “Electric current. Current strength."
Lesson plan.
Organizing time.
Updating knowledge.
Learning new material.
Consolidation.
Summarizing.
1. Organizational moment.
Preparing to learn new material.
Today we will get acquainted with the concepts: electric current, current strength and the conditions necessary for the existence of electric current.
3. Updating knowledge.
On the screen is slide number 2.
You all know the phrase “electric current” well, but more often we use the word “electricity”. These concepts have become part of our lives so long ago that we don’t even think about their meaning. So what do they mean?
In previous lessons, we partially touched on this topic, namely, we studied stationary charged bodies. As you remember, this branch of physics is called electrostatics.
On the screen is slide number 3.
Okay, now think about it. What does the word "current" mean?
Movement! This means “electric current”, this is the movement of charged particles. It is this phenomenon that we will study in the following lessons.
In 8th grade, we partially studied this physical phenomenon. Then we said that: “electric current is the directed movement of charged particles.”
Today in the lesson we will consider the simplest case of directional movement of charged particles - direct electric current.
Learning new material.
For the emergence and existence of a constant electric current in a substance, the presence of free charged particles is necessary, the movement of which in a conductor causes the transfer of electric charge from one place to another.
On the screen is slide number 5.
However, if charged particles undergo random thermal motion, such as free electrons in a metal, then charge transfer does not occur, which means there is no electric current.
On the screen is slide number 6.
Electric current occurs only with the ordered (directed) movement of charged particles (electrons or ions).
On the screen – slide number 7.
How to make charged particles move in an orderly manner?
We need a force acting on them in a certain direction. As soon as this force ceases to act, the ordered movement of particles will cease due to the electrical resistance exerted to their movement by ions of the crystal lattice of metals or neutral molecules of electrolytes.
On the screen – slide number 8.
So where does this power come from? We said that charged particles are acted upon by the Coulomb force F = q E (the Coulomb force is equal to the product of the charge and the intensity vector), which is directly related to the electric field.
On the screen is slide number 9.
Typically, it is the electric field inside the conductor that causes and maintains the ordered movement of charged particles. If there is an electric field inside a conductor, then there is a potential difference between the ends of the conductor. When the potential difference does not change over time, a constant electric current is established in the conductor.
On the screen – slide number 10
This means that in addition to charged particles, for the existence of an electric current, the presence of electric field.
When a potential difference (voltage) is created between any points of a conductor, the balance of charges will be disrupted and a movement of charges will occur in the conductor, which is called an electric current.
On the screen – slide number 11.
Thus, we have established two conditions for the existence of electric current:
presence of free charges,
presence of an electric field.
On the screen is slide number 12.
So: ELECTRIC CURRENT is the directed, ordered movement of charged particles (electrons, ions and other charged particles.). Those. electric current has a certain direction. The direction of current is taken to be the direction of movement of positively charged particles. It follows that the direction of the current coincides with the direction of the electric field strength vector. If the current is formed by the movement of negatively charged particles, then the direction of the current is considered opposite to the direction of movement of the particles. (This choice of current direction is not very successful, since in most cases the current represents the ordered movement of electrons - negatively charged particles. The choice of current direction was made at a time when nothing was known about free electrons in metals.)
On the screen is slide number 13.
We do not directly see the movement of particles in a conductor. The presence of electric current must be judged by the actions or phenomena that accompany it.
On the screen is slide number 14.
Thermal effect of electric current. The conductor through which the current flows heats up (an incandescent light bulb lights up);
On the screen is slide number 15.
Magnetic effect of electric current. A conductor with current attracts or magnetizes bodies, turns perpendicular to the wire with current, a magnetic arrow;
On the screen is slide number 16.
Chemical action of electric current. An electric current can change the chemical composition of a conductor, for example, releasing its chemical constituents (hydrogen and oxygen are released from acidified water poured into a U-shaped glass vessel).
The magnetic effect is the main one, as it is observed in all conductors, the thermal effect is absent in superconductors, and the chemical effect is observed only in solutions and melts of electrolytes.
On the screen is slide number 17.
Like many physical phenomena, electric current has a quantitative characteristic called current strength: if through the cross section the conductor carries a charge ∆q during the time ∆t, then the average value of the current is: I=∆q/∆t(current strength is equal to the ratio of charge to time).
Thus, the average current strength is equal to the ratio of the charge ∆q passing through the cross section of the conductor during the time interval ∆t to this period of time.
In the SI (International System) the unit of current is the ampere, denoted 1 A = 1 C/s (One ampere is equal to the ratio of 1 coulomb per 1 second)
Please note: if the current does not change over time, then the current is called constant.
On the screen is slide number 18.
The current strength can be a positive value if the direction of the current coincides with the conventionally selected positive direction along the conductor. Otherwise the current is negative.
On the screen is slide number 19.
To measure current strength, a device is used - an ammeter. The design principle of these devices is based on the magnetic action of current. An ammeter is connected in an electrical circuit in series to the device from which the current is to be measured. A schematic representation of an ammeter is a circle with the letter A in the center.
On the screen is slide number 20.
In addition, the current strength is related to the speed of directional movement of particles. Let's show this connection.
Let a cylindrical conductor have a cross section S. Let us take the direction from left to right as the positive direction in the conductor. The charge of each particle will be considered equal to q 0. The volume of the conductor, limited by cross sections 1 and 2 with a distance ∆L between them, contains particles N = n·S·∆L, where n is the concentration of particles.
On the screen is slide number 21.
Their total charge in the selected volume is q = q 0 ·n·S·∆L (the charge is equal to the product of the particle charge by concentration, area and distance). If particles move from left to right with an average speed v, then in a time ∆t = ∆L/v equal to the ratio of distance to speed, all particles contained in the volume under consideration will pass through cross section 2. Therefore, the current strength is found using the following formula.
I = ∆q/∆t = (q 0 ·n·S·∆L·v)/∆L= q 0 ·n·S·v
On the screen is slide number 22.
Using this formula, let's try to determine the speed of ordered movement of electrons in a conductor.
V = I/( e·n·S),
Where e– electron charge modulus.
On the screen is slide number 23.
Let the current strength I = 1A, and the cross-sectional area of the conductor S = 10 -6 m 2, for copper the concentration n = 8.5 10 28 m -3. Hence,
V=1/(1.6 ·10 -19 · 8.5·10 28 ·10 -6)=7·10 -5 m/s
As we see, the speed of ordered movement of electrons in a conductor is low.
On the screen is slide number 24.
To estimate how small, p Let us imagine a very long current circuit, for example a telegraph line between two cities separated from each other, say, 1000 km. Careful experiments show that the effects of the current in the second city will begin to manifest themselves, that is, the electrons in the conductors located there will begin to move, approximately 1/300 of a second after their movement along the wires in the first city began. It is often said, not very strictly, but very clearly, that current travels through wires at a speed of 300,000 km/s. This, however, does not mean that the movement of charge carriers in the conductor occurs at this enormous speed, so that an electron or ion, which in our example was in the first city, will reach the second in 1/800 of a second. Not at all. The movement of carriers in a conductor almost always occurs very slowly, at a speed of several millimeters per second, and often even less. We see, therefore, that we need to carefully distinguish and not confuse the concepts of “current speed” and “speed of charge carriers.”
On the screen is slide number 25.
Thus, the speed that we call “current speed” for brevity is the speed of propagation of changes in the electric field along the conductor, and not at all the speed of movement of charge carriers in it.
Let us explain this with a mechanical analogy. Let's imagine that two cities are connected by an oil pipeline and that in one of these cities a pump has begun to operate, increasing the oil pressure in that place. This increased pressure will spread through the liquid in the pipe at high speed - about a kilometer per second. Thus, in a second, particles will begin to move at a distance of, say, 1 km from the pump, after two seconds - at a distance of 2 km, in a minute - at a distance of 60 km, etc. After about a quarter of an hour, oil will begin to flow out of the pipe in the second city. But the movement of the oil particles themselves occurs much more slowly, and several days may pass before any specific oil particles reach from the first city to the second. Returning to electric current, we must say that the “speed of current” (the speed of propagation of the electric field) is similar to the speed of pressure propagation through the oil pipeline, and the “velocity of carriers” is similar to the speed of movement of the particles of the oil itself.
5. Consolidation.
On the screen – slide number 26
Today in class we looked at the basic concept of electrodynamics:
Electricity;
Conditions necessary for the existence of electric current;
Quantitative characteristics of electric current.
On the screen – slide No. 27
Now let's look at solving typical problems:
1. The tile is included in the lighting network. How much electricity flows through it in 10 minutes if the current in the supply cord is 5A?
Solution: Time in SI system 10 minutes = 600s,
By definition, current is equal to the ratio of charge to time.
Hence, the charge is equal to the product of current and time.
Q = I t = 5A 600 s = 3000 C
On the screen – slide No. 28
2. How many electrons pass through the filament of an incandescent lamp in 1 s when the current in the lamp is 1.6 A?
Solution: The charge of an electron is e= 1.6 10 -19 C,
The entire charge can be calculated using the formula:
Q = I t – charge is equal to the product of current and time.
The number of electrons is equal to the ratio of the total charge to the charge of one electron:
N = q/ e
this implies
N = I t / e= 1.6A 1s/1.6 10 -19 Cl = 10 19
On the screen – slide No. 29
3. A current of 1 A flows through a conductor for a year. Find the mass of electrons that passed through the cross section of the conductor during this period of time. Ratio of electron charge to its mass e/m e = 1.76 10 +11 C/kg.
Solution: The mass of electrons can be defined as the product of the number of electrons and the mass of the electron M = N m e. Using the formula N = I t / e(see previous problem), we find that the mass is equal to
М = m e I t / e= 1A 365 24 60 60s/(1.76 10 +11 C/kg) = 1.8 10 -4 kg.
On the screen – slide No. 30
4. In a conductor with a cross-sectional area of 1 mm 2, the current is 1.6 A. The electron concentration in the conductor is 10 23 m -3 at a temperature of 20 0 C. Find the average speed of directional movement of electrons and compare it with the thermal speed of electrons.
Solution: To determine the average speed of directional movement of electrons, we use the formula
Q = q 0 n S v t (the charge is equal to the product of the particle charge by concentration, area, speed and time).
Since I = q/t (current strength is equal to the ratio of charge to time),
Then I = q 0 n S v => v= I/ (q 0 n S)
Let us calculate and obtain the value of the speed of electron movement
V= 1.6A/(10 23 m -3 10 -6 m 1.6 10 -19 C) = 100 m/s
M v 2 /2 = (3/ 2) k T => (it follows from here)
= 11500 m/s
The speed of thermal movement is 115 times greater.
Summarizing.
On the screen – slide number 31
Write down your homework.
V.A.Kasyanov Physics textbook 11th grade. §1,2, problems §2 (1-5).
On the screen – slide number 32.
Thank you for your attention. We wish you success in your independent exercises on this topic!
Abstract checked
Methodologist of the Education Department:_____________________________________________
Expert Council of the Yerevan State Pedagogical University:__________________________________________
Date of:_____________________________________________________________
Signatures:__________________________________________________________
Target: disclosure of the material nature of the electric field and the formation of the concept of electric field strength
Lesson objectives: familiarize students with the power characteristics of the electric field;
To form informal knowledge in the interpretation of the concept of “electric field strength;
Foster a conscious attitude to learning and interest in studying physics.
Equipment: light metal sleeve made of foil, plexiglass stick, plumes on a stand, electrophore machine, ball on a silk thread, capacitor plates, presentation, flash animation
During the classes
- Repetition of what has been learned
- State Coulomb's law
- What is the physical meaning of the coefficient k?
- Determine the limits of applicability of Coulomb's law?
- Physical dictation. Law of conservation of electric charge. Coulomb's law. (mutual verification)
- Learning new material
1.Is it possible to create an electric charge?
2. Do we create an electric charge during electrification?
3. Can a charge exist separately from a particle?
4. A body whose total positive charge of particles is equal to the total negative charge of particles is…..
5. The force of interaction of charged particles with increasing charge of any of these particles…..
6. When a charge is placed in a medium, the interaction force between them….
7. With an increase in the distance between charges by 3 times, the interaction force......
8. The quantity characterizing the electrical properties of the medium is called...
9. In what units is electric charge measured?
(1, Yes; 2. No; 3. No; 4. Neutral; 5. Increases; 6. Decreases; 7. Will decrease by 9 times; 8. Dielectric constant; 9. In pendants)
- Learning new material
The interaction of charges according to Coulomb's law is an experimentally established fact. ( slide 1 )However, it does not reveal the physical picture of the interaction process itself. And it does not answer the question of how the action of one charge on another occurs.
Experiment 1 (with sleeve) Slowly bring a vertically located plexiglass plate to a light metal foil sleeve suspended on a thread, having previously charged it with wool.
-What's happening?( there is no contact, but the sleeve has deviated from the vertical)
Experiment 2 ( electrophore machine, plates of a spherical capacitor, tennis ball suspended on a silk thread ) Having charged the plates, we observe the movement of the ball between them. Why?
This is how interaction occurs at a distance. Maybe it's the air between the bodies?
Experiment 3 (watching a video fragment, flash animation) While pumping out the air, we observe that the leaves of the electroscope continue to repel each other.
What can be concluded? ( air does not participate in the interaction )
How then does interaction take place?
Faraday gives the following explanation:
There is always an electric field around every electric charge. ( slide 2)
To characterize E.P. you need to enter values.
The first characteristic of the Field is TENSION.
Let us turn again to Coulomb’s law ( slide 3 )
Let us consider the effect of the field on the charge introduced into the field of the test charge.
……………………………………………
Thus, if we look at the ratio, we will get a value that will characterize the action of the field at a given point.
Denoted by the letter E.
- Tension E.P.
Tension E.P. does not depend on the magnitude of the charge, a vector quantity (force characteristic of the field) It shows with what force the field acts on a charge placed in this field.
Substituting the expression for force into the formula, we obtain the expression for the field strength of a point charge
How can you characterize a field created by several charges?
We must use the vector addition of the forces acting on the charge introduced into the field and obtain the resulting E.P. intensity. This case is called the SUPERPOSITION PRINCIPLE
(slide 6)
Experiment 4. Experiments on demonstrating the spectra of electric fields. (1. Experiments with sultans installed on insulating stands and charged from an electric foil machine. 2. Experiments with capacitor plates to which paper strips are glued at one end.)
It is convenient to represent the electric field by graphic lines - POWER LINES. FIELD LINES are lines indicating the direction of the force acting in this field on a positively charged particle placed in it ( slides 9,10,11)
Field lines created by positively (a) and negatively (b) charged particles
The most interesting case is E.P. created between two long charged plates. Then a homogeneous E.P. is created between them.
Explanation of the principle of superposition, using a graphical representation ( slides11,12,13)
III.Consolidation of knowledge, abilities, skills
1. Review questions
? Analysis of questions:
a) How should we understand that an electric field exists at a given point?
b) How should we understand that the tension at point A is greater than the tension at point B?
c) How should we understand that the intensity at a given point in the field is 6 N/kl?
d) What value can be determined if the strength at a given point in the field is known?
? 2. Analysis of qualitative problems [Tulchinsky M.E. Qualitative problems in physics in high school. - M.: Education, 1972.]:
800. Two charges of equal magnitude are located at a certain distance from each other. In what case is the tension at a point lying half the distance between them greater: if these charges are like or unlike? ? (Dissimilar. With point charges of the same name, the tension will be zero.)
801. (When a high voltage current is turned on, a static electric charge appears on the bird’s feathers, as a result of which the bird’s feathers bristle and diverge (like the tassels of a paper plume connected to an electrostatic machine). This frightens the bird, it flies off the wire.)
? Analysis of calculation problems [Rymkevich A.P. Collection of problems in physics, grades 10-11. - M.: Bustard, 2003.]:
698. (200 V/m)
699. What force acts on a 12 nC charge placed at a point where the electric field strength is 2 kN/Cl? (24 µN)
Summing up the lesson.
Homework:
- Textbook Physics 10 G.A. Myakishev, B.B. Bukhovtsev § 88-89
- Rymkevich A.P. No. 703, 705
View document contents
“Lesson summary with presentation. Electric field. Electric field strength. The principle of superposition of fields"
ELECTRIC FIELD.
Tension
ELECTRIC FIELD - it is a special form of matter. It is created by electrical charges at rest and manifests itself by acting on other electrical charges.
tension E.P. does not depend on the magnitude of the charge, vector quantity (field strength characteristic)
- field strength of a point charge
- superposition principle - the field strength created by a system of charges is equal to the vector sum of the field strengths created by each charge separately
POWER LINES- these are lines indicating the direction of the force acting in this field on a positively charged particle placed in it
Field lines created by positively (a) and negatively (b) charged particles
TENSION LINES are continuous lines whose tangents at each point coincide with the field strength vector at that point
Properties of tension lines
- The lines are not closed. Start with + and end with –
- The lines don't cross
- Where the lines are thicker, the field is stronger
- Why do birds fly off high voltage wires when the current is turned on?
- Two charges of equal magnitude are located at some distance from each other. In what case is the tension at a point lying half the distance between them greater: if these charges are like or unlike? ?
- At some point in the field, a force of 0.4 μN acts on a charge of 2 nC. Find the field strength at this point.
- What force acts on a 12 nC charge placed at a point where the electric field strength is 2 kN/C
| Lesson summary on the topic: “The effect of an electric field on electric charges. Electric field energy" Full name: Tyutyugina N. A. |
| Place of work: State Budgetary Institution of the Republic of Kazakhstan "KSS "Simeiz" |
| Position: physics teacher |
| Subject: physics |
| Grade: 8 |
| Topic and lesson number in the topic: topic 1, lessons No. 3, 4 |
| Basic tutorial: |
Goals:
Educational: know and understand the concepts: electric charge, electric field, discreteness of charge, interaction of charges.
Educational: promote the development of speech, thinking, cognitive and general labor skills; promote mastery of scientific research methods: analysis and synthesis.
Educational: to form a conscientious attitude towards educational work, positive motivation for learning, and communication skills; contribute to the education of humanity, discipline, and aesthetic perception of the world.
Lesson type: A lesson in learning new material.
Lesson form : combined lesson.
Lesson Methods : verbal, visual, practical.
During the classes
1. Organizational stage.
2. Updating basic knowledge.
3. Stage of acquiring new knowledge.
4. Stage of generalization and consolidation of new material. .
5. Final stage. 3 min.
3.
An electric field is a special form of matter through which the interaction of electrically charged particles occurs.
The introduction of the concept of an electric field was necessary to explain the interaction of electric charges, that is, to answer the questions: why do forces acting on charges arise, and how are they transferred from one charge to another?
The concepts of electric and magnetic fields were introduced by the great English physicist Michael Faraday. According to Faraday's idea, electric charges do not act on each other directly. Each of them creates an electric field in the surrounding space. The field of one charge acts on another charge, and vice versa. As you move away from the charge, the field weakens.
With the introduction of the concept of field in physics, the theory of short-range action was established, the main difference of which from the theory of long-range action is the idea of the existence of a certain process in space between interacting bodies, which lasts a finite time.
This idea was confirmed in the works of the great English J.C. Maxwell, who theoretically proved that electromagnetic interactions must propagate in space with a finite speed - s, equal to the speed of light in vacuum (300,000 km/s). Experimental proof of this statement was the invention of radio.
An electric field arises in the space surrounding a stationary charge, just as a magnetic field arises around moving charges - currents or permanent magnets. Magnetic and electric fields can transform into each other, forming a single electromagnetic field. The electric field (like the magnetic field) is only a special case of the general electromagnetic field. Alternating electric and magnetic fields can exist without the charges and currents that generated them. An electromagnetic field transfers a certain amount of energy, as well as momentum and mass. Thus, the electromagnetic field is a physical entity that has certain physical properties.
So, the nature of the electric field is as follows:
1. The electric field is material; it exists independently of our consciousness.
2. The main property of the electric field is its effect on electric charges with some force. This action establishes the fact of its existence. The effect of a field on a unit charge - field strength - is one of its main characteristics, by which the distribution of the field in space is studied.
The electric field of stationary charges is called electrostatic. Over time, it does not change, is inextricably linked with the charges that generated it, and exists in the space surrounding them.
Definition. Physical quantity equal to force ratio F, with which the electric field acts on the test charge q, to the value of this charge, is called the electric field strength and is denoted E.Review questions
1. What is an electric field?
2. What are the main properties of the electric field?
3. What field is called electric?
4. What is the electric field strength called?
5. What is the electric field strength?
6. How to determine the field strength of a point charge?
7. What electric field is called uniform?
