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.
Decision. 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, on the first ball the charge was 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?
Decision. 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 stationary 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 what formula and within what allowable limits the field strength of a conducting ball can be calculated.
Summing up the lesson
Homework: §92 - 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.
Decision. 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?
Decision. 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 stationary 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 what formula and within what allowable limits the field strength of a conducting ball can be calculated.
Summing up the lesson
Homework: §92 - 94.
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- The purpose of the lesson: to find out the level theoretical knowledge students
Equipment: multimedia projector, interactive board, presentation for the lesson
DURING THE CLASSES
I. Knowledge Test
1. Coulomb's law (frontal survey):
a) Name the scientist who experimentally established the law of interaction of point electric charges in vacuum. ( French scientist C. Coulomb in 1795).
b) What was the name of the device with which Coulomb's law was experimentally established? ( Torsional dynamometer, or as it was then called torsion balances).
c) Formulate Coulomb's law.
d) Write the formula of Coulomb's law.
e) With which law from the section "Mechanics" can an analogy be drawn for Coulomb's law? ( With the law of gravity:;).
f) Indicate the limits of applicability of the Coulomb law ( a) the charges must be stationary, b) point).
II. New topic
1. Electric field:
a) Referring to the completed home experimental tasks, the teacher brings students to the concept of an electric field ( space around a charged body) and its discovery.
Students remember that you can detect an electric field using a magnetic needle made of paper (or foil).
The teacher immediately shows that the electric field can also be detected using an electrometer.
As a conclusion of previous observations, students are led to the statement that the electric field, like any kind of matter, is material and exists independently of our consciousness.(By analogy, we recall the gravitational field).
2. Characteristics of the electric field
a) tension.
(Students are reminded that any kind of matter can be characterized in some way. The same can be done with an electric field).
One of the characteristics of the electric field is the intensity:
It is specified that The electric field strength is the power characteristic of the electric field.
b) The intensity of a unit charge. (According to Coulomb's law):
; is the intensity of a single charge.
c) The principle of superposition (overlay) of fields:
3. Graphical representation of electric fields
Field lines of force are lines of tension.
Field lines of force start on a positive (+) and end on a negative (-) charge or ?.
Field lines can be used to show a graphical representation of electric fields. Practically visual obtaining of field lines can be shown with the help of an electrophore machine and electric sultans.
In turn, connecting the electric sultans with the electrophore machine, we get a clear demonstration of the graphical representation of electric fields. Simultaneously with the experiment, a graphical representation of the field is projected onto the screen with the help of a codoscope.
I. Single charge field: (demonstration)
a) field of a single positive charge: (graphical representation)
b) Field of a single negative charge:
c) the field of two opposite charges (experiment)
d) the field of two opposite charges (graphical representation)
c) the field of two similar charges (experience)
d) the field of two similar charges (graphical representation)
It must be said that, unlike other vector quantities, tension, as a vector quantity, is characterized not by the length of the vector, but by the density of drawing lines of tension per unit area. (through overhead -on screen or shown on the board graphic image demonstrating this)
III. Work to consolidate and control knowledge
Physical dictation:
1. The law of conservation of electric charge (formula)
2. Coulomb's law (formula)
3. The type of matter that carries out the interaction of charged bodies located at a certain distance from each other (Electrostatic field)
4. Unit of charge (1 C)
5. Instrument for detecting electric field (Electrometer).
6. The formula of the electric field strength (.
7. The unit of measurement of tension ().
8. What instrument did Sh. Coulomb use to study and derive his law? (By torsion dynamometer or torsion balance).
9. Power characteristic of the electric field (Tension).
10. Show a graphical representation of the electric field of a single positive charge.
Collect student responses.
IV. On the board is prepared, while closed from students, a brief record of the problem that needs to be solved.
Task: A force of 0.015 N acts on the charge C at a certain point in the electric field. Determine the field strength at this point.
Given: Solution:
V.Summing up the lesson
V. Homework§ 92-93
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"Physics lesson. The theme of the lesson is "Electric field. Tension. The idea of short-range action." »
Physics lesson. Topic: Electric field.
Near action and action at a distance
Spreads
with the final
speed
Spreads instantly
Interaction through the void
Interaction through the field
Electric field
Idea: M. Faraday
Theory: J. Maxwell
q 1
q 2
close interaction
t is the transmission time of electromagnetic interactions
r is the distance between charges
s is the propagation speed of electromagnetic interactions (300,000 km / s)
Electric field:
- financially: exists independently of us and our knowledge about it (radio waves)
- created by charges
Main property: acts on q with some F
Electric field strength
[E]==
The field strength is equal to the ratio of the force with which the field acts on a point charge to the module of this charge.
E T
- field strength of a point q 0
Principle of superposition of fields
E 2
E=E 1 +E 2 +E 3 + … + En
E 1
The field of a charged ball.
Inside the ball E=0
+ + - + E= const homogeneous email field Lines of force: not closed; do not intersect; start at + q ; end in -q ; continuous; thicker; where E is greater. 7" width="640" Lines of force (SL - lines of tension) of the electric field
SL - continuous lines, tangent to which at each point. through which they pass coincide with E .
E= const homogeneous email field
Field lines: not closed; do not intersect; start on + q; end on -q; continuous; thicker; where E more.
Subject: Electric field. Electric field strength
The purpose of the lesson : 1) Recall the concept of an electric field. Form the concept of electric field strength
The development of logical and abstract thinking, the ability to reason, defend one's point of view, draw conclusions.
Education of an active life position, the formation of a scientific worldview.
Equipment : Educational presentation, video film, interactive whiteboard
During the classes
1. Introduction . Defining the goals and objectives of the lesson
2. Homework control
Students choose their own topic.
Working with the periodic table
How many electrons are in the water molecule H 2 O (10)
How many electrons are in a molecule carbon dioxide CO 2 (28)
How many protons are in the iron oxide Fe 2 O 3 molecule (56)
The experience of Charles Coulomb
Formulate Coulomb's Law
The physical meaning of the coefficient of proportionality
Limits of applicability of Coulomb's law
Tasks for the application of Coulomb's law
How will the force of the Coulomb interaction of two point charges change with an increase in each charge three times? (increase by 9)
How will the interaction force between charges change if the distance is doubled? (increase 4 times)
How will the force of the Coulomb interaction of two point charges change with an increase in each charge three times, if the distance is reduced by 2 times? (increase 36 times)
Two identical metal balls are charged with charges equal in magnitude but opposite in sign. The balls were brought into interaction and moved apart. Determine the force of interaction between charges. (0)
3. Explanation of new material. (Conversation)
We answered the question How charged bodies interact. However, nothing was said about the way in which the action of one charge on another is carried out.
Let's first discuss the question of how the interaction between bodies is generally carried out.
1) Theory of action at a distance ( Bodies interact with each other at a distance, and the interaction is transmitted instantly)
2) Short range theory(An intermediate agent is required for the interaction to take place)
What theory is most suitable for describing the interaction of charged bodies?
3) Michael Faraday. ( There is an electric field
James Maxwell. ( Created a theory electromagnetic field)
4) Electric field - a special form of matter
Properties:
Acts on a charge with some force
Generated by electrical charges
Detected by the action on electric charges
5) Tension - power characteristic of the electric field
Definition: Tension - physical quantity, equal to the ratio the force with which the electric field acts on the test electric charge, to the value of this charge.
Units:(On my own) N/C
Tension vector direction coincides with the direction of the force acting from the electric field on a positive charge
Draw tension vectors at points A and B
6) Derivation of the formula for the field strength of a point charge. (On one's own)
7) The principle of superposition of fields
8) Electric field strength lines
Lines, tangents to which coincide with coincide with the direction of the intensity vector at a given point of the field
9) Properties of electric field strength lines
§ 91-94
Exercise 17 (1)
Starts on positive and ends on negative charges
Do not intersect
What new did you learn? (Formulas)
6) Homework
Grading
