The purpose of the lesson: to acquaint students with the history of the struggle between the concepts of close action and action at a distance; with flawed theories, introduce the concept of tension electric field, to form the ability to depict electric fields graphically; use the principle of superposition to calculate the fields of a system of charged bodies.
During the classes
Examination homework method of doing independent work
Option 1
1. Can you create or destroy electric charge? Why? Explain the essence of the law of conservation of electric charge.
2. There are two bodies in the air, which have equal negative electric charges, the bodies repel each other with a force of 0.9 N. The distance between the charges is 8 cm. Calculate the mass of excess electrons in each body, as well as their number.
Solution. m = m0 N = 9.1 10-31 5 1012= 4.5 10-19 (kg); N = √Fr2/k e ; N= 5 1012 (electrons)
Option-2
1 Why are dissimilar bodies electrified during friction, while homogeneous bodies are not electrified?
2 Three conductive balls brought into contact, the first ball had a charge of 1.8 10-8 C, the second one had a charge of 0.3 10-8 C, the third ball had no charge. How is the charge distributed between the balls? With what force will two of them interact in a vacuum at a distance of 5 cm from one another?
Solution. q1+q2+q3= 3q; q = (q1+q2+q3)/3q = 0.5 10-8(C)
F=kq2/r2; F= 9 10-5 (H)
Learning new material
1. Discussion of the issue of transferring the impact of one charge to another. The speeches of the "supporters" of the theory of short-range action (the field propagates at the speed of light) and the theory of action at a distance (all interactions propagate instantly) are heard. The performances of students are accompanied by a demonstration of experiments on the interaction of electrified bodies. Students can ask questions to supporters of one theory or another.
The teacher helps students to draw the right conclusions, leads students to the formation of the concept of an electric field.
2. Electric field - A special form of matter that exists independently of us, our knowledge of it.
3. The main property of the electric field- action on electric charges with a certain force.
| electrostatic field | The electrostatic field of fixed charges does not change completely and is inextricably linked with the charges that form it. | ||
| Electric field strength: E= F/ Q | The ratio of the force with which the electric field acts on a test positive charge to the value of this charge. Vector Ē̄̄̄̄̄̄ coincides with the direction of the force acting on the positive charge. | ||
| Electric field strength of a point charge. E =Q0/4πξ0ξr2 |
The electric field strength of a point charge at a certain point in space is directly proportional to the charge modulus of the field source and inversely proportional to the square of the distance from the field source to the given point in space. | ||
| lines of force electrostatic field | These are lines whose tangents at each point of the field coincide with the direction of the field strength at that point. | ||
| Principle of superposition of fields: E \u003d E1 + E2 + E3 + ...
|
When fields are applied from several point charges, an electrostatic field is formed, the strength of which at any point is equal to the geometric sum of the strengths from each of the component fields. | ||
| Demonstration of experience: "Justification of the principle of superposition of fields" | Hang a “trial charge” (foam plate) on a nylon thread. Influence the "trial charge" with a charged body. Then bring another charged body and observe its effect on the "trial charge". Remove the first charged body and observe the action of the second charged body. Make a conclusion. | ||
Independent work with the book.
1. Read in the textbook the definition of electric field lines.
2. Consider carefully the figures 181 - 184, which show examples of lines of tension of various charged bodies and systems of bodies.
3. Answer the questions.
A) How is the modulus of the intensity vector displayed in the figures? On what outward sign can you distinguish a field with intense action?
B) Where do the electric field lines begin and where do they end?
C) Are there breaks in the lines of tension?
D) How are the electric field lines located relative to the surface of a charged body?
e) In what case can the electric field be considered uniform?
E) Compare the pattern of field lines of a point charge and a uniformly charged ball.
G) Find out with the help of what formula and within what acceptable limits it is possible to calculate the field strength of a conducting ball.
Summing up the lesson
Homework: §92 - 94.
Subject: PhysicsSection of the discipline of the exam: _________ _
Total lessons in the topic -_18___
№ lesson from this topic _4____
Lesson topic « Electricity. Current strength »
Lesson summary provided
FULL NAME. _ __ Bryleva Lilia Zakirzyanovna_
Academic title, position: Physics teacher
Place of work: MOU secondary school No. 6
Physics lesson summary
"Electricity. The strength of the current.
Lesson Objectives:
Educational - give the concept of electric current and find out the conditions under which it occurs. Enter quantities characterizing the electric current.
Developing - to form intellectual skills to analyze, compare the results of experiments; to activate the thinking of schoolchildren, the ability to independently draw conclusions.
educational - development cognitive interest to the subject, expanding the horizons of students, to show the possibility of using the knowledge gained in the lessons in life situations.
Type of lesson: a lesson in the assimilation of new knowledge.
Equipment: presentation on the topic “Electric current. The strength of the current.
Lesson plan.
Organizing time.
Knowledge update.
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 an electric current.
3. Actualization of knowledge.
On the screen - slide number 2.
All of you are well aware of the phrase "electric current", but more often we use the word "electricity". These concepts have long and firmly entered our lives that we do not even think about their meaning. So what do they mean?
In the past lessons, we partially touched on this topic, namely, we studied motionless charged bodies. As you remember, this branch of physics is called electrostatics.
On the screen - slide number 3.
Okay, now think about it. What does the word "current" mean?
Motion! So - "electric current", this is the movement of charged particles. It is this phenomenon that we will study in the following lessons.
In the 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 the directed movement of charged particles - a 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, during the movement of which in the conductor an electric charge is transferred from one place to another.
On the screen - slide number 5.
However, if charged particles perform random thermal motion, as, for example, free electrons in a metal, then charge transfer does not occur, which means that there is no electric current.
On the screen - slide number 6.
An electric current arises only with an 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?
You need a force acting on them in a certain direction. As soon as this force ceases to operate, then the ordered movement of particles will stop due to the electrical resistance exerted by their movement by ions crystal lattice metals or neutral electrolyte molecules.
On the screen – slide number 8.
So where does this power come from? We said that the charged particles are affected 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 - slide number 9.
Usually, 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 the conductor, then there is a potential difference between the ends of the conductor. When the potential difference does not change with 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 creating a potential difference (voltage) between any points of the conductor, the balance of charges will be disturbed and charges will move in the conductor, which is called electric current.
On the screen – slide number 11.
Thus, we have established two conditions for the existence of an electric current:
the presence of free charges,
the presence of an electric field.
On the screen - slide number 12.
So: ELECTRIC CURRENT - directed, ordered movement of charged particles (electrons, ions and other charged particles.). Those. electric current has a certain direction. The direction of movement of positively charged particles is taken as the direction of the current. 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. (Such a choice of the direction of the current is not very successful, since in most cases the current is an ordered movement of electrons - negatively charged particles. The choice of the direction of the current was made at a time when nothing was known about free electrons in metals.)
On the screen - slide number 13.
We do not directly see the motion of particles in a conductor. The presence of an electric current has to be judged by the actions or phenomena that accompany it.
On the screen - slide number 14.
Thermal effect of electric current. The conductor through which the current flows heats up (the incandescent electric bulb glows);
On the screen - slide number 15.
Magnetic action of electric current. A current-carrying conductor attracts or magnetizes bodies, turns a magnetic needle perpendicular to the current-carrying wire;
On the screen - slide number 16.
Chemical action of electric current. Electric current can change chemical composition conductor, for example, to release 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, since it is observed in all conductors, the thermal effect is absent in superconductors, and the chemical effect is observed only in electrolyte solutions and melts.
On the screen - slide number 17.
How many physical phenomena electric current has quantitative characteristic, called current strength: if through the cross section conductor during the time ∆t the charge ∆q is transferred, then the average value of the current strength is: I=∆q/∆t(current is equal to the ratio of charge to time).
Thus, the average current strength is equal to the ratio of the charge ∆q that has passed through the cross section of the conductor in a time interval ∆t to this time interval.
In the SI (international system), the unit of current strength is the ampere, denoted 1 A \u003d 1 C / s (One ampere is equal to the ratio of 1 coulomb per 1 second)
Please note: if the current strength does not change with time, then the current is called constant.
On the screen - slide number 18.
The current strength can be a positive value if the direction of the current coincides with the conventionally chosen positive direction along the conductor. Otherwise, the current is negative.
On the screen - slide number 19.
An ammeter is used to measure current. The design principle of these devices is based on magnetic action current. IN electrical circuit The ammeter is connected in series with the device from which the current is to be measured. A schematic representation of an ammeter is a circle, in the center is the letter A.
On the screen - slide number 20.
In addition, the current strength is related to the speed of the directed movement of particles. Let's show this connection.
Let a cylindrical conductor have a cross section S. For the positive direction in the conductor, we take the direction from left to right. The charge of each particle will be considered equal to q 0. The volume of the conductor bounded 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 - slide number 21.
Their total charge in the chosen volume is q = q 0 n S ∆L (the charge is equal to the product of the particle charge and the concentration, area and distance). If the 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 velocity, all particles contained in the volume under consideration will pass through cross section 2. Therefore, the current strength is found by the following formula.
I = ∆q/∆t = (q 0 n S ∆L v)/∆L= q 0 n S v
On the screen - slide number 22.
Using this formula, let's try to determine the speed of the ordered movement of electrons in a conductor.
V = I/( e n S),
Where e is the electron charge modulus.
On the screen - slide number 23.
Let the current strength I \u003d 1A, and the cross-sectional area of \u200b\u200bthe conductor S \u003d 10 -6 m 2, for copper the concentration n \u003d 8.5 10 28 m -3. Consequently,
V=1/(1.6 10 -19 8.5 10 28 10 -6)=7 10 -5 m/s
As we can see, the speed of the ordered movement of electrons in the conductor is small.
On the screen - slide number 24.
To estimate how small, n Let us imagine a very long current circuit, for example, a telegraph line between two cities, separated from each other by, say, 1000 km. Careful experiments show that the effects of the current in the second city will begin to appear, i.e., 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 the current propagates through the 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 tremendous speed, so that the electron or ion, which was in our example in the first city, will reach the second in 1/800 of a second. Not at all. The movement of carriers in a conductor is almost always very slow, at a speed of several millimeters per second, and often even less. We see, therefore, that it is necessary to carefully distinguish and not confuse the concepts of "current velocity" and "velocity of charge carriers".
On the screen - 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 the speed of movement of charge carriers in it.
Let us explain what has been said mechanical analogy. Let us imagine that two cities are connected by an oil pipeline and that a pump starts working in one of these cities, increasing the oil pressure in this place. This increased pressure will propagate through the liquid in the pipe at a 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, in 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 is much slower, and it can take several days for some specific oil particles to reach the first city to the second. returning to electric current, we must say that the "speed of the current" (the speed of propagation of the electric field) is similar to the speed of propagation of pressure through the oil pipeline, and the "velocity of the carriers" is similar to the speed of movement of the particles of the oil itself.
5. Fixing.
On the screen - slide number 26
Today in the lesson we considered the basic concept of electrodynamics:
Electricity;
Conditions necessary for the existence of an electric current;
Quantitative characteristic of electric current.
On the screen - slide number 27
Now consider the solution of 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: SI time 10 minutes = 600s,
By definition, current is equal to the ratio of charge to time.
Hence, the charge is equal to the product of the current and the time.
Q \u003d I t \u003d 5A 600 s \u003d 3000 C
On the screen - slide number 28
2. How many electrons pass through the spiral of an incandescent lamp in 1 s at a lamp current strength of 1.6A?
Solution: The charge of an electron is e\u003d 1.6 10 -19 C,
The total charge can be calculated using the formula:
Q \u003d I t - the charge is equal to the product of the current strength 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\u003d 1.6A 1s / 1.6 10 -19 C \u003d 10 19
On the screen – slide number 29
3. A current of 1 A flows through the conductor during the year. Find the mass of electrons that have passed through the cross section of the conductor during this period of time. The ratio of an electron's 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 the previous problem), we get that the mass is equal to
M = m e I t / e\u003d 1A 365 24 60 60 s / (1.76 10 +11 C / kg) \u003d 1.8 10 -4 kg.
On the screen – slide number 30
4. In a conductor whose cross-sectional area is 1mm 2, the current strength is 1.6A. The concentration of electrons in the conductor is 10 23 m -3 at a temperature of 20 0 C. Find the average speed of the directed movement of electrons and compare it with the thermal speed of electrons.
Solution: To determine average speed directional motion of electrons, we use the formula
Q = q 0 n S v t (the charge is equal to the product of the particle charge and concentration, area, velocity and time).
Since I \u003d 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)
Calculate and get the value of the speed of electrons
V \u003d 1.6A / (10 23 m -3 10 -6 m 1.6 10 -19 C) \u003d 100 m/s
M v 2 /2 = (3/ 2) k T => (hence follows)
= 11500 m/s
The speed of thermal motion is 115 times greater.
Summarizing.
On the screen – slide number 31
Write down your homework.
V.A. Kasyanov Physics textbook grade 11. §1,2, tasks §2 (1-5).
On the screen – slide number 32.
Thanks for attention. We wish you success in independent exercises on this topic!
Abstract checked
Methodologist of the Education Department: _____________________________________
Expert Council of YSPU: __________________________________________
Date of:_____________________________________________________________
Signatures:________________________________________________________________
Topic : Electric field. Electric field strength. Principle of superposition of fields
The purpose of the lesson: continue the formation of the concept of "electric field", introduce its main characteristic; to study the principle of superposition of electric fields.
During the classes:
1. Organizational moment. Setting goals and objectives for the lesson.
2. Knowledge check:
Physical dictation
Electrification of tel. The law of conservation of charge. Coulomb's Law
What is the name of the branch of physics that studies motionless charged bodies? /electrostatics/
What interaction exists between charged bodies, particles? /electromagnetic/
What physical quantity determines the electromagnetic interaction? /electric charge/
Does the magnitude of the charge depend on the choice of the frame of reference? /Not/
Is it possible to say that the charge of the system is the sum of the charges of the bodies included in the system? /Can/
What is the name of the process that leads to the appearance of electric charges on the bodies? /Electrification/
If a body is electrically neutral, does this mean that it contains no electric charges? /Not/
Is it true that in a closed system algebraic sum charges of all bodies of 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? /Not/
Do we create an electric charge when we electrify? /Not/
Can a charge exist independently of a particle? /Not/
A body, the total positive charge of the particles of which is equal to the total negative charge of the particles, is ... /Neutral/
How will the force of interaction of charged particles change with an increase in the charge of any of these particles? /Increase/
How will the interaction force change when charges move into the medium? /Decrease/
How will the interaction force change with an increase in the distance between the charges by 3 times? /Decrease by 9 times /
What is the name of the quantity that characterizes electrical properties environment? /Dielectric permittivity of the medium/
What is the unit of measure for electric charge? /in pendants/
3. Studying new material
Electric field
The interaction of charges according to the Coulomb 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 is carried out.
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.
An electric field is a field created by stationary electric charges.
An electric field can be detected by introducing given point trial (positive) charge.
A test point charge is a charge that does not distort the field under study (does not cause a redistribution of charges that create the field).
Electric field properties:
Affects 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 kind of matter, the movement of which does not obey the laws of Newtonian mechanics. This type of matter has its own laws, properties that cannot be confused with anything else in the surrounding world.
Electric field strength
Physical quantity, equal to the ratio the force with which an electric field acts on a test chargeq, to the value of this charge, is calledelectric field strength
and denoted 
:
.
The unit of tension is 1N/C or 1V/m.
The vectors of the electric field and the Coulomb force are codirectional.
An electric field whose intensity is the same at all points in space is called homogeneous.
Lines of tension (lines of force) - lines, tangents to which at each point coincide with the direction of the vector .
In order to characterize not only the direction, but also the value of the electrostatic field strength with the help of tension lines, they are carried out with a certain density: the number of tension lines penetrating a unit of surface area perpendicular to the tension lines must be equal to the modulus of the vector .
If the field is created by a point charge, then the lines of tension are radial straight lines coming out of the charge if it positive, and included in it, if the charge negative.
Principle of superposition of fields
Experience shows that if an electric charge q the electric fields of several sources act simultaneously, then the resulting force turns out to be equal to the sum acting from the side of 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 Sat. tasks, ed. Rymkevich №№ 696,697,698
Homework: §92,93,94
The purpose of the lesson: to acquaint students with the history of the struggle between the concepts of close action and action at a distance; with shortcomings of theories, to introduce the concept of electric field strength, to form the ability to depict electric fields graphically; use the principle of superposition to calculate the fields of a system of charged bodies.
During the classes
Checking homework by doing independent work
Option 1
1. Is it possible to create or destroy an electric charge? Why? Explain the essence of the law of conservation of electric charge.
2. There are two bodies in the air, which have equal negative electric charges, the bodies repel each other with a force of 0.9 N. The distance between the charges is 8 cm. Calculate the mass of excess electrons in each body, as well as their number.
Solution. m = m0 N = 9.1 10-31 5 1012= 4.5 10-19 (kg); N = √Fr2/k e ; N= 5 1012 (electrons)
Option-2
1 Why are dissimilar bodies electrified during friction, while homogeneous bodies are not electrified?
Three conductive balls brought into contact, the first ball had a charge of 1.8 10-8 C, the second had a charge of 0.3 10-8 C, the third ball had no charge. How is the charge distributed between the balls? With what force will two of them interact in a vacuum at a distance of 5 cm from one another?
Solution. q1+q2+q3= 3q; q = (q1+q2+q3)/3q = 0.5 10-8(C)
F=kq2/r2; F= 9 10-5 (H)
Learning new material
1. Discussion of the issue of transferring the impact of one charge to another. The speeches of the "supporters" of the theory of short-range action (the field propagates at the speed of light) and the theory of action at a distance (all interactions propagate instantly) are heard. The performances of students are accompanied by a demonstration of experiments on the interaction of electrified bodies. Students can ask questions to supporters of one theory or another.
The teacher helps students to draw the right conclusions, leads students to the formation of the concept of an electric field.
2. Electric field - a special form of matter that exists independently of us, our knowledge of it.
3. The main property of the electric field- action on electric charges with a certain force.
| electrostatic field | The electrostatic field of fixed charges does not change completely and is inextricably linked with the charges that form it. | ||
| Electric field strength: E= F/ q | The ratio of the force with which the electric field acts on a test positive charge to the value of this charge. Vector Ē̄̄̄̄̄̄ coincides with the direction of the force acting on the positive charge. | ||
| Electric field strength of a point charge. E =q0/4πξ0ξr2 | The electric field strength of a point charge at a certain point in space is directly proportional to the charge modulus of the field source and inversely proportional to the square of the distance from the field source to the given point in space. | ||
| Electrostatic field lines | These are lines whose tangents at each point of the field coincide with the direction of the field strength at that point. | ||
| Principle of superposition of fields: E \u003d E1 + E2 + E3 + ... | When fields are applied from several point charges, an electrostatic field is formed, the strength of which at any point is equal to the geometric sum of the strengths from each of the component fields. | ||
| Demonstration of experience: "Justification of the principle of superposition of fields" | Hang a “trial charge” (foam plate) on a nylon thread. Influence the "trial charge" with a charged body. Then bring another charged body and observe its effect on the "trial charge". Remove the first charged body and observe the action of the second charged body. Make a conclusion. | ||
Independent work with the book.
1. Read in the textbook the definition of electric field lines.
2. Consider carefully the figures 181 - 184, which show examples of lines of tension of various charged bodies and systems of bodies.
3. Answer the questions.
A) How is the modulus of the intensity vector displayed in the figures? By what external sign can one distinguish a field with intense action?
B) Where do the electric field lines begin and where do they end?
C) Are there breaks in the lines of tension?
D) How are the electric field lines located relative to the surface of a charged body?
e) In what case can the electric field be considered uniform?
E) Compare the pattern of field lines of a point charge and a uniformly charged ball.
G) Find out with the help of what formula and within what acceptable limits it is possible to calculate the field strength of a conducting ball.
Summing up the lesson
Homework: §92 - 94.
- The purpose of the lesson: to form ideas about the potentiality of the electrostatic field, to establish the independence of the work of electrostatic forces from the shape of the trajectory, to introduce the concept of potential, to find out physical meaning potential differences, output ...
- The purpose of the lesson: to control the knowledge and skills of students acquired in the study of this topic. Course of the lesson Organizational moment Option - 1 (level - 1) 1. Two point ...
- The purpose of the lesson: based on the model of a metal conductor, to study the phenomenon of electrostatic induction; find out the behavior of dielectrics in an electrostatic field; introduce the concept of dielectric permittivity. Lesson progress Checking home...
- The purpose of the lesson: to form an idea of an electromagnetic wave, as the interaction of electric and magnetic fields; compare electromagnetic waves from mechanical waves according to a number of characteristics common to the two ...
- The purpose of the lesson: to develop skills in solving problems using the concepts of tension, potential, the work of an electric field to move a charge; continue to form the ability to think, compare, draw conclusions, draw up ...
- The purpose of the lesson: to form students' understanding of the electric and magnetic fields, as a single whole - the electromagnetic field. Lesson progress Checking homework by testing ...
- The purpose of the lesson: to derive a formula for the relationship between the electric field strength and the potential difference, to introduce the concept of equipotential surfaces, to form the ability to apply the theoretical knowledge gained to solving qualitative ...
- The purpose of the lesson: to find out the level theoretical knowledge students
Topic: Electric field. Electric field strength. Principle of superposition of fields
Target: disclosure of the material nature of the electric field and the formation of the concept of electric field strength
Lesson objectives: to acquaint students with the power characteristic of the electric field;
∙ to form informal knowledge in the interpretation of the concept of “electric field strength;
∙ to cultivate a conscious attitude to learning and interest in the study of physics.
Lesson: learning new material
Equipment: light metal foil sleeve, plexiglass stick, sultans on a stand, electrophore machine, ball on a silk thread, capacitor plates, presentation, flash animation
During the classes
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. The 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, the total positive charge of the particles of which is equal to the total negative charge of the particles, is ... ..
5. The strength of the interaction of charged particles with an increase in the charge of any of these particles ... ..
6. When a charge is placed in a medium, the force of interaction 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 the electric charge measured?
(1, Yes; 2. No; 3. No; 4. Neutral; 5. Increases; 6. Decreases; 7. Reduced by 9 times; 8. Dielectric constant; 9. In pendants)
Learning new material
The interaction of charges according to the Coulomb 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 is carried out.
Experiment 1 (with a sleeve) We slowly bring a vertically located plexiglass plate to a light metal foil sleeve suspended on a thread, having previously charged it by rubbing 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, a tennis ball suspended on a silk thread ) After charging the plates, we observe the movement of the ball between them. Why?
This is how communication works at a distance. Maybe it's the air that is between the bodies?
Experiment 3 (viewing a video clip, flash animation) Pumping out the air, we observe that the leaves of the electroscope still repel each other.
What can be the conclusion? ( air does not participate in the interaction )
How then is the interaction carried out?
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 the values.
The first characteristic of the Field is INTENSITY.
Let us turn again to Coulomb's law ( slide 3 )
Consider the action of the field on the charge introduced into the test charge field.
……………………………………………
Thus, if we look at the ratio, we will get a value that will characterize the action of the field at a given point.
Designated with the letter E.
E.P. tension
E.P. tension does not depend on the magnitude of the charge, 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 the force into the formula, we obtain an expression for the field strength of a point charge
How can one characterize the field created by several charges?
It is necessary to use the vector addition of the forces acting on the charge introduced into the field and get the resulting E.P. This case is called the SUPERPOSITION PRINCIPLE.
(slide 6)
Experiment 4 Experiments to demonstrate the spectra of electric fields. (1. Experiments with sultans mounted on insulating stands and charged from an electrofoil machine. 2. Experiments with capacitor plates, to which paper strips are glued at one end.)
The electric field is conveniently depicted by graphic lines - LINES OF FORCE. LINES OF FORCE 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 of the field 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 ( slides 11,12,13)
III. Consolidation of knowledge, skills, skills
Review questions
∙ Analysis of questions:
a) How should we understand that there is an electric field 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 is it to be understood that the strength at a given point of the field is 6 N/cl?
d) What value can be determined if the intensity at a given point of the field is known?
∙ 2. Analysis of qualitative tasks
800. Two charges of the same modulus are at some distance from each other. In which case is the intensity at a point lying halfway between them greater: if these charges are of the same name or opposite? (Opposite. With the same point charges, the intensity will be zero.)
801. Why do birds fly off the high voltage wire when the current is turned on? (When a high voltage current is turned on, a static electric charge arises on the bird's feathers, as a result of which the bird's feathers bristle and diverge (like the brushes of a paper plume connected to an electrostatic machine diverge). This frightens the bird, it flies off the wire.)
∙ Analysis of calculation problems [Rymkevich A.P. Collection of problems in physics, 10-11 cells. - 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 charge of 12 nC 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. Koishibaev, 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, 10-11 cells. - M .: Bustard, 2003
V.A.Volkov. To help the school teacher.
