§ 1 Electrification of bodies
In this lesson, we will discuss the concept of electricity, and find out where this word came from.
Now it is impossible to imagine the modern world without electricity, and even more so without a computer, refrigerator, TV, electric lighting, etc. All these devices work with the use of electric current and surround us everywhere in our life. Technologies initially independent of electricity, such as the internal combustion engine, are gradually becoming history, and electric motors are actively taking their place. So where did the word "electricity" come from?
The word "electric" comes from the word "electron" (Greek), it means "amber" (fossil resin). Although, of course, it should be noted that there is no direct connection between amber and all electrical phenomena, so how did the ancient scientists get such an association?
According to one of the legends, the daughter of the famous philosopher of Ancient Greece Thales of Miletus, who lived in IV BC, spun wool with a spindle made of an expensive stone - amber. She told Thales that she could not clean the spindle from small pieces of wool, fluff, threads. Moreover, the more she cleans with her woolen tunic, the more debris sticks to the spindle. Thales could not immediately answer his daughter's question.
In the evening, he decided to try to clean the spindle and saw that sparks were visible when rubbing it in the dark. “There is something to think about and reflect on with my students,” Thales said.
The phenomenon, which was noticed by the girl, Thales called electricity (from the word electron - "amber").
When rubbing a piece of amber on a woolen piece of cloth or a glass stick on paper, you can hear a slight crackle, and even see small sparks in the dark, and the stick itself helps to attract small objects to itself.
A body that attracts other bodies to itself after rubbing is said to be given an electric charge or that it is electrified.
Electrification is a phenomenon in which bodies acquire the properties of attracting other bodies.
Bodies made of different substances can become electrified. So, you can easily electrify by rubbing sticks made of sulfur, ebonite, plastic on wool. The bodies are rubbed only in order to increase the area of their contact.
Two bodies are always involved in electrification, and both are electrified. So, when rubbing a glass rod and a piece of paper, both the rod and the paper are electrified. Consequently, paper, like glass, attracts small objects to itself.
An electric charge is possessed by a body that attracts or repels other bodies. Such a body is said to be charged (has a charge).
Charge is a property of bodies or the ability to interact electromagnetically.
An electroscope is a device that allows you to detect the presence of a charge in a body and evaluate it.
An insulated conductive rod is the main part of the electroscope; an arrow is fixed on it, which is able to rotate freely. When a charge appears, the arrow and the rod are charged with charges of the same sign, as a result of which they, repelling, create an angle of deflection, the value of which is proportional to the received charge.
§ 2 Methods of electrifying bodies
The electrification of bodies occurs in various cases.
Methods for electrifying bodies:
·contact
Let's take a look at some of them.
Ebonite gets a negative charge, and wool - a positive charge, if you rub an ebony stick on wool. With the help of an electroscope, the presence of these charges is detected. To achieve this result, it is necessary to touch the rod of the electroscope with an ebonite stick or woolen cloth. In this case, part of the charge of the test body is transferred to the rod. Note that there is a momentary electrical current.
You can consider the interaction of two paper sleeves suspended on a thread, one charged from an ebony stick, and the other from a woolen cloth.
Note that they are attracted to each other. This means that bodies with opposite charges attract. Not every substance can transfer electric charges.
Conductors are called substances through which charges are transferred, and substances through which charges are not transferred are called non-conductors - dielectrics (insulators). This can be found out with the help of an electroscope, if you connect it with a charged body, substances of various kinds.
Describing electrification by friction, only good insulators are always taken for the experiment - amber, ebonite, glass, silk. The question is why? Let us explain: in insulators, where a charge has arisen, it remains there, and cannot pass through the entire surface of the body to other bodies in contact with it. If both rubbing bodies are metals with insulated handles, then the experiment will fail, since it is impossible to separate them from each other at once over the entire surface.
Due to the roughness of the surface of the bodies at the moment of separation, some last points of contact should remain, through which excess electrons escape at the last moment, and both metals become uncharged.
Consider electrification by contact. If we immerse a ball of paraffin in distilled water and then take it out, then both the paraffin and the water will be charged.
So why did the electrification of water and paraffin occur without friction? Let us explain: it turns out that during electrification by friction, the contact area only increases and the distance between the atoms of the rubbing bodies decreases. In the experiment with water and paraffin, roughness cannot prevent the approach of their atoms.
Thus, we can say that friction is not a prerequisite for the electrification of bodies. What is the reason that electrification occurs in these cases?
§ 3 The principle of operation of the electrophore machine
The work of an electrophore machine is based on the electrification of the body through influence. An electrified body interacts with any electrically neutral conductor.
When such bodies approach each other due to the electric field of a charged body, a redistribution of charges occurs in the second body. The charges, which are opposite in sign to the charged body, are located closer to the charged body. Further from the charged body in the conductor (sleeve or cylinder) there are charges of the same name as the charged body.
The distance to the positive and negative charges in the cylinder from the ball is different, therefore the forces of attraction prevail, the cylinder deflects towards the electrified body. If you touch the far side of the body from the charged ball with your hand, the body will jump to the charged ball. By reducing the repulsive forces, the electrons jump to the hand.
§ 4 Brief summary of the lesson
Electrification is a phenomenon in which bodies acquire the properties of attracting other bodies.
Electrification can occur in the following ways:
· Contact;
· Through influence;
· On impact;
· Friction.
Substances are: electropositive and electronegative.
It is possible to predict what charges the interacting bodies will receive, if we know the belonging of the substances.
Friction only increases the contact area.
Substances - conductors and dielectrics.
Insulators accumulate charges at the points of contact (where they were formed).
The charges in the conductors are distributed evenly throughout the entire volume.
List of used literature:
Images used:
Even in ancient times it was known that if you rub amber on wool, it begins to attract light objects to itself. Later, the same property was found in other substances (glass, ebonite, etc.). This phenomenon is called electrification, and bodies capable of attracting other objects to themselves after rubbing are electrified. The phenomenon of electrification was explained on the basis of the hypothesis of the existence of charges that an electrified body acquires.
Simple experiments on the electrification of various bodies illustrate the following provisions.
The state of electrification can be transferred from one body to another, which is associated with the transfer of electrical charge. In this case, a larger or smaller charge can be transferred to the body, that is, the charge has a magnitude. During electrification by friction, both bodies acquire a charge, one $ - $ positive, and the other $ - $ negative. It should be emphasized that the absolute values of the charges of bodies electrified by friction are equal, which is confirmed by numerous experiments.
It became possible to explain why bodies are electrified (i.e. charged) during friction after the discovery of the electron and the study of the structure of the atom. As you know, all substances consist of atoms, which, in turn, consist of elementary particles $ - $ negatively charged electrons, positively charged protons and neutral particles $ - $ neutrons. Electrons and protons are carriers of elementary (minimum) electric charges. Protons and neutrons (nucleons) make up the positively charged nucleus of the atom, around which negatively charged electrons revolve, the number of which is equal to the number of protons, so that the atom as a whole is electrically neutral. Under normal conditions, bodies consisting of atoms (or molecules) are electrically neutral. However, in the process of friction, part of the electrons that have left their atoms can move from one body to another. In this case, the movement of electrons does not exceed interatomic distances. But if, after friction, the bodies are disconnected, then they will be charged: the body that gave up some of its electrons will be charged positively, and the body that acquired them $ - $ negatively.
So, bodies are electrified, that is, they receive an electric charge when they lose or acquire electrons. In some cases, electrification is due to the movement of ions. In this case, new electric charges do not arise. There is only a division of the existing charges between the electrifying bodies: part of the negative charges passes from one body to another.
Abstract of a physics lesson in grade 8.
Topic: “Electrification of tel. Two kinds of charge ”.
Lesson type: a lesson in the assimilation of new knowledge.
The purpose of the lesson: to form the concept of electrification in schoolchildren; show the existence of two types of charges and explain their interaction; to formulate measures to prevent electrification when performing hairdressing work.
Educational tasks:
Developing tasks:
Educational tasks:
Equipment: ebony and glass sticks, fur, silk, tripod, sultans, pieces of paper, polyethylene, paper, rubber, combs, cotton, wool, nylon, plexiglass rulers.
Lesson plan
1. Introductory speech of the teacher
Guys, we know that physics is studying physical phenomena, which include:
Mechanical
Thermal
Electrical
Magnetic
Light
Sound.
In the seventh grade, we began to get acquainted with mechanical phenomena, we devoted almost 2 quarter to the study of thermal phenomena, and now we will closely engage in the study of electrical phenomena. What are we going to study with you? You will answer this question yourself. Choose from the proposed physical phenomena electrical.
I post phenomena on the board:
Snow melting
Lightning
Rainbow
Electricity
Rain
Vehicle movement.
We fill in the scheme with examples:
Electrical phenomena
Let's complement the diagram with an example of an electrical phenomenon that you encounter when performing your professional duties as a hairdresser. This is electrification. Is this a useful or harmful phenomenon in your activity? Today we must work out measures to prevent electrification when performing hairdressing work. But for this we need to get acquainted in great detail with the phenomenon of electrification. Therefore, the topic of our lesson is “Electrification of bodies. Two kinds of charges ”. We write down the topic of the lesson in a notebook.
Each of you, by the end of the lesson, should learn to explain what an electric charge and electrification are, how charged bodies interact with each other, and this will help you develop measures to prevent and reduce electrification when performing hairdressing.
2. Learning new material
Let's write a lesson plan:
2) the concept of electrification
3) methods of electrification
7) measures to prevent and reduce electrification when performing hairdressing work.
In ancient Greece in the 6th century BC, in the beautiful city of Miletus, the philosopher Thales of Miletus lived. And then one eveninghis beloved daughter approaches him. Explain why my threads get tangled when I work with an amber spindle, dust and straws stick to the yarn. It is very uncomfortable. Thales takes a spindle, rubs it and sees small sparks. From this moment, the history of the development of the term "electricity" begins. At first, the property of attracting small objects was attributed only to amber (petrified resin of coniferous trees). From the name of which the word electricity comes from, because the Greek. elektron-amber. (writing on the board).
The English physician and naturalist Ulyam Gilbert found out in the late 16th and early 17th centuries that friction can electrify many substances: diamond, sapphire, sealing wax and that they attract not only straws, but also metals, wood, leaves, pebbles, clods of earth, and even water and oil.
Let's check if different bodies can really become electrified. Pick up the combs and rub them on your hair. After that, bring it to the pieces of paper. We observe the phenomenon of electrification. Take a ruler lying on the table, rub it on the paper, bring it to the small pieces of paper. We observe the phenomenon of electrification. Inflate the balls lying on your table, rub them on the plastic, bring them to the New Year's tinsel.
Demonstrations. An ebony stick rubbed on fur attracts the Sultan's leaves. A glass stick, rubbed against silk, attracts pieces of paper.
An ebony stick, rubbed against the fur, attracts a stream of water. (according to the figure in the textbook page 58 fig. 28)
We draw conclusions from all these experiments. (Write in a notebook)
1. Not only amber can be electrified, but also other substances.
2. Electrification - phenomena in which bodies acquire the property of attracting other bodies.
3. Two bodies are involved in electrification.
Let's continue.
Demonstration. We electrify the ebonite stick on the fur. Let's bring it to the pieces of paper. The leaves are attracted. Let's bring the fur. The leaves are attracted.
Take a ruler and rub the rubber on it. Bring the ruler over to the pieces of paper. Bring the rubber to the leaves.
We draw one more conclusion. (Write in a notebook)
4. Both bodies are electrified.
So, we already know what electrification is. Let's get acquainted with her ways.
Let's fill in the diagram.
Electrification methods
Friction Contact Impact
When performing previous experiments, we have already met with you one of the ways. Let's call it. (Friction)
Demonstration. We rub the ebony stick on the fur and bring it to the sultan. It is electrified. We check by presenting pieces of paper.
In this case, we no longer performed friction to electrify the sultan, we just touched him. This way of electrifying is touching.
Try it yourself. Take a ruler and rub it against the fur. Touch the Sultan. Bring the Sultan to the pieces of paper.
Demonstration. Hit the polyethylene with a ruler several times. Let's bring the ruler to the pieces of paper. They are attracted. Demonstrated electrification by blow.
So, the body can be electrified by friction, impact, contact.
Let's continue.
Gently rub the plastic wrap hanging from the tripod with a piece of paper. Electrify paper and plastic strips. To do this, put a plastic strip on a paper strip and smooth it. Separate them and bring them to each other. How do they interact?
Alternately, bring the paper and plastic strips to the strip on a tripod. Observe their interaction.
Demonstration. We electrify the ebonite stick against the rubber and bring it to the plastic strip. How do they interact? We electrify the ebonite stick on the fur. Let's bring it to the strip. How do they interact?
Thus, electrified bodies can either attract or repel. What could cause such a difference in interaction?
Based on the experiments performed, we can conclude that any body contains two kinds of electric charges. If the charges in the body are equal, then the body does not exhibit electrical properties. These properties are found only during electrification, which leads to an imbalance of electrical charges in the body.
The concept of the types of charge was introduced in 1747 by the American scientist Benjamin Franklin. Ebony stick from electrification on wool and fur acquires a negative charge. The charge, which forms on a glass rod, rubbed against silk, Franklin called positive. But in Franklin's time there was only natural silk and natural fur. Today it is sometimes difficult to distinguish natural silk and faux fur. Even different grades of paper electrify ebonite in different ways. Ebonite acquires a negative charge from contact with wool (fur) and nylon, but positive from contact with polyethylene.
Two kinds of charge
Negative positive
(ebonite on fur) (glass on silk)
We have already learned that there are two kinds of charge, positive and negative. Let's find out how they interact.
Demonstration. We electrify the ebonite stick on the fur. We will receive a negative charge, we will report it to the Sultan. Let's charge a glass stick on silk and bring it to the sultans. The sultan will be attracted to the wand. We electrify the ebonite stick on the fur, bring it to the Sultan. Sultan's leaves push off.
We draw a conclusion and write it down in a notebook:
Charges of the same sign repel
Charges of different signs are attracted.
3. Primary control:
Now let's check what you have learned about the interaction of charged bodies.
Answer the questions on the cards.
Which paper cylinders shown in the picture are charged and which are not? (Fig. 1)
Which cylinders are charged with one sign? (Fig. 1)
Which cylinders are charged with a different sign? (Fig. 1)
Find the error (Fig. 2)
Determine the sign of the charge on the unsigned ball (Fig. 3).
Now let's see how you learned what electrification is.
Answer the test questions.
Test.
a) heats up
b) is cooled
c) comes into motion
2 ... Electric charges are ...
A) positive.
B) negative.
d) different.
3. If an electrified body is repelled
a) positive;
c) negative
d) not charged.
a) heating
b) friction
c) stretching
d) contact
e) blow.
First, we work on the test ourselves, and then we check everything together.
4. Anchoring
We already know what electrification is, what its methods are. We found out what charges exist and how they interact. Now let's name the reasons for electrifying hair when doing hairdressing.
We write it down in a notebook.
- rubbing hair on clothing
Rubbing hair on the combs
Drying your hair with a hairdryer
Insufficient air humidity.
Knowing the reasons for the electrification of hair, let's try to name the measures to prevent this. First, let's try to experimentally determine which clothes are best to reduce the electrification of our hair.
Take the wool in your hand and rub it against your hair. Then bring the fur to your hair. Pay attention to the force with which the hair is attracted to the fur.
Take a cotton in your hand and rub your hair with it. Then bring the cotton to your hair. Pay attention to how hard the hair is attracted to the cotton.
Take silk in your hand and rub your hair with it. Then bring the cotton to your hair. Pay attention to the force with which the hair is attracted to the silk.
Make a conclusion about which material reduces the electrification of the hair.
Let's mark in the notebook the first measure to prevent electrification of the hair.
Choose clothes made of cotton, linen.
Pick up a plastic comb and rub it against your hair, then bring it up to your hair. Since during electrification, one body is charged positively, and the other negatively, if you carry the comb to your hair, they will be attracted. Do the same with a wooden comb.
Make a conclusion about which combs are best to use.
Write it down in a notebook.
Use combs made of wood.
How to reduce electrification when drying with a hair dryer?
Use conditioners.
What to do with air inworking room?
Humidify the air.
Today in the lesson we have coped with the task. The measures that we have developed today will help you in your professional activities.
5. Recording homework and assigning marks
Prepare a message on the use of electrification in everyday life and industry.
Annex 1
Electrified body | About plexiglass | About rubber | About polyethylene | About paper | About nylon |
Plexiglass | |||||
Rubber | |||||
Polyethylene | |||||
Paper | |||||
Nylon |
Electrified body | About plexiglass | About rubber | About polyethylene | About paper | About nylon |
Plexiglass | |||||
Rubber | |||||
Polyethylene | |||||
Paper | |||||
Nylon |
Electrified body | About plexiglass | About rubber | About polyethylene | About paper | About nylon |
Plexiglass | |||||
Rubber | |||||
Polyethylene | |||||
Paper | |||||
Nylon |
Electrified body | About plexiglass | About rubber | About polyethylene | About paper | About nylon |
Plexiglass | |||||
Rubber | |||||
Polyethylene | |||||
Paper | |||||
Nylon |
LESSON PLAN
1) the origin of the word "electricity"
2) the concept of electrification
3) methods of electrification
4) types of electric charge
5) interaction of charged bodies
6) the reasons for electrification during hairdressing
Test.
a) heats up
b) is cooled
c) comes into motion
d) attracts other bodies to itself
A) positive.
B) negative.
c) positive and negative
d) different.
From an ebony stick, rubbed against the fur, then it is charged:
a) positive;
c) negative
d) not charged.
4. The body can be electrified ...
a) heating
b) friction
c) stretching
d) contact
e) blow.
Test.
a) heats up
b) is cooled
c) comes into motion
d) attracts other bodies to itself
2. Electric charges are ...
A) positive.
B) negative.
c) positive and negative
d) different.
3. If an electrified body is repelled
From an ebony stick, rubbed against the fur, then it is charged:
a) positive;
c) negative
d) not charged.
4. The body can be electrified ...
a) heating
b) friction
c) stretching
d) contact
e) blow.
LESSON PLAN
1) the origin of the word "electricity"
2) the concept of electrification
3) methods of electrification
4) types of electric charge
5) interaction of charged bodies
6) the reasons for electrification during hairdressing
7) measures to prevent and reduce electrification when performing hairdressing
LESSON PLAN
1) the origin of the word "electricity"
2) the concept of electrification
3) methods of electrification
4) types of electric charge
5) interaction of charged bodies
6) the reasons for electrification during hairdressing
7) measures to prevent and reduce electrification when performing hairdressing
DISCIPLINE REVIEW QUESTIONS
_____________________PHYSICS_________________________
Electrification of tel. Methods for electrifying tel. Coulomb's law. Dielectric constant of the medium.
Electrifying the body is charging.
Methods:
Friction (touch) - bodies are charged with the same name.
Influence - charged differently
Irradiation: ultraviolet, X-ray, etc.
The force of interaction of two point charges is directly proportional to the product of the magnitudes of these charges, inversely proportional to the square of the distance between them, depends on the medium, is directed along the straight line connecting these charges
ε = F_0 / F_av
How many times the force of interaction of two point charges in a vacuum is greater than their interaction in a medium.
ε = ε_av / ε_0
Electric field as a special kind of matter. Graphical representation of an electric field. Electric field strength. Homogeneous field.
An electric field is a special type of matter through which static charges interact.
Properties:
Created by charge
Act on charge
Charge related
Detect with a single positive test charge
It is limitless
Distributed in any environment
Depicted by ley lines
E = F / q
The electric field strength at a given point is numerically equal to F, acting on a unit positive test charge placed at a given point of the electric field.
SI:
[E] = N / CL
A uniform electric field is a field, at each point of which the strength is the same.
The work of the electric field when moving the charge. Potential charge energy. Potential. Potential difference and voltage. Relationship between field strength and voltage.
φ = А_ (1 → ∞) / q
The potential of the electric field at a point is numerically equal to A, which the electric field performs over a unit positive test charge when moving from one point to infinity.
φ = Е_р / q
SI:
[φ] = J / C = V
Voltage is the potential difference between two point charges of an electric field.
U = A_ (1 → 2) / q
The potential of the electric field at a point is numerically equal to A, which the electric field performs over a unit positive test charge when moving from a given point to another.
A = E * q * l
A = U * q
U * q = E * q * l
U = E * l
Conductor in an electric field. Equipotential surface. Dielectric in an electric field. Dielectric polarization. Electrostatic protection.
An electrified conductor has charges on the surface. An electrified conductor destroys E_out (ϵ_ (el.p) inside the conductor is zero).
Equipotential surface - surface of equal potential.
Dielectric polarization - dipole rotation in an electric field.
Electrostatic protection - placing devices that are sensitive to an electric field inside a closed conductive shell to shield from an external electric field.
The electrical capacity of the conductor. Capacitors. Types and connection of capacitors. The energy of the electric field of a charged capacitor.
The electrical capacity of a conductor is the ability of a conductor to accumulate charges on its surface.
С = q / φ
The electrical capacity of the conductor is numerically equal to q, which must be placed on the conductor so that φ = 1V.
In SI:
[C] = Cl / V = F
Outside system units:
1 pF = 1 * 〖10〗 ^ (- 12) Ф
1nF = 1 * 〖10〗 ^ (- 9) F
1mkF = 1 * 〖10〗 ^ (- 6) F
The capacitor is a system of two conductors separated by a dielectric
Capacitor types:
Air
Paper
Electrolytic
Salty
Ceramic
Follow each other. The presence of nodal points.
W_el = (q * U) / 2
W_el = (C * V ^ 2) / 2
Electric current and the condition for its existence. Strength and current density. Units of their measurement. Dependence of current strength from an electronic point of view. Ohm's law for a section of a chain.
Electric current-directed (ordered) movement of charged particles.
Conditions of existence:
- the presence of free electric charges in the environment
-creation of an electric field in the environment.
The amperage is a value that shows how much charge has passed through the cross section of the conductor in 1 second.
I = q / t
Si: [I] = C / sec = A
Outside system units:
1μA = 1 * 〖10〗 ^ (- 6) A
1mA = 1 * 〖10〗 ^ (- 3) A
1kA = 1 * 〖10〗 ^ 3 A
Current density indicates the number of charges per unit of conductor cross-sectional area.
j = I / S
SI: [j] = A / m ^ 2
Outside system units:
1A / 〖mm〗 ^ 2 = 1 * 〖10〗 ^ (6 A / m ^ 2)
1A / 〖cm〗 ^ 2 = 1 * 〖10〗 ^ 4 A / m ^ 2
1A / 〖dts〗 ^ 2 = 1 * 〖10〗 ^ 2 A / m ^ 2
Let us establish what the current strength in the conductor depends on from an electronic point of view
I = n_0 * S * e * v
n_0-kind of conductor
S-thin or thick
e-view of the conductor (tv, liquid, gas).
Ohm's law:
I = U / R
The strength of the current in a section of the circuit is directly proportional to the voltage at the ends of this section, inversely proportional to the resistance of this section of the circuit.
C:
[R] = V / A = Ohm
Outside system units:
1 kΩ = 1 * 〖10〗 ^ 3Ω
1 mΩ = 1 * 〖10〗 ^ 6Ω
Closed electrical circuit. External and internal sections of the chain. Electromotive force of a source of electrical energy. Ohm's law for a complete circuit with one e.d.s.
Closed electrical circuit - consumer + source
The outer section of the circuit is the consumer of electricity.
The inner section of the circuit is a source of electricity
ε = A_st / q
The EMF of the source is numerically equal to A, which is performed by external forces when a unit charge moves inside the source.
Ohm's law for a closed circuit
I = ε / (R + r)
The strength of the current in the entire circuit is directly proportional to the EMF of the source and is inversely proportional to the sum of the external and internal sections of the circuit.
Conductor resistance. Dependence of resistance on the type, size of the conductor and temperature. Superconductivity. Conductor resistivity and units.
1 / (n_0 + e + u) = p-conductor resistivity
R = ρ * l / S
[p] = Ohm * m
Superconductivity is the phenomenon of a sharp drop in resistance to zero near absolute zero
Serial and parallel connection of consumers and sources of electrical energy.
Consumer connection
Serial Parallel
I_tot = I_1 = I_2 = I_3 I_tot = I_1 + I_2
U_total = U_1 + U_2 + U_3 U_total = U_1 + U_2
R_total = R_1 + R_2 + R_3 1 / R_total = 1 / R_1 + 1 / R_2
R_total = (R_1 * R_2) / (R_1 + R_2)
Feature: one after another Feature: the presence of anchor points
Linking sources
Serial parallel
ε_b = ε_1 + ε_2 + ε_3 = ε_1 * nε_b = ε_1 = ε_2 = ε_3
r_b = r_1 + r_2 + r_3 = r_1 * n 1 / r_b = 1 / r_1 + 1 / r_2 + 1 / r_3
I_b = (ε_1 * n) / (R + r_1 * n) I_b = ε_1 / (R + r_1 / m)
Work and power of electric current. Units of their measurement. Thermal effect of the current. Joule-Lenz law. Short circuit.
A_ (electric current) = U * I * t = P * t
A_ (electric current) depends on the strength of the current, time and does not depend on what type of energy it turns into
Unit measurements:
[A] = B * A * sec = J = W * sec
Outside system units:
1 Wh = 3.6 * 〖10〗 ^ 3J
1 kWh = 3.6 * 〖10〗 ^ 6J
1 mWh = 3.6 * 〖10〗 ^ 9J
Power is a physical quantity that shows a unit of work done per unit of time.
P = U * I
SI:
[P] = W
Outside system units:
1kW = 1 * 〖10〗 ^ 3W
1 mW = 1 * 〖10〗 ^ 6W
Joule Lenz's Law
Q = I ^ 2 * R * t
The amount of heat released in the conductors is directly proportional to the square of the current strength, resistance and the time the current passes through the conductor.
I_kz = ε / r
Thermionic emission. Exit work. Contact potential difference. Thermocouple and its application. Thermoelectromotive force.
The phenomenon of discharge of charge from a conductor under the influence of high temperature is called emission.
A_out = e * ∆φ
e = 1.6 * 〖10〗 ^ (- 19)
Unit measurements: [A_out] = Cl * B = J
Off-system units: 1eV = e * 1V = 1.6 * 〖10〗 ^ (- 19) J
∆φ-contact potential difference arises:
With different work output
With a different amount of e
A thermocouple is a device consisting of two homogeneous metals, the ends of which are soldered.
Application:
1.Power source
2.Generator "Chamomile"
3.Thermometer
1.If t_a = t_0, then ∆φ_1 = ∆φ_2, I = 0
2.t_a> t_b, then ∆φ_1> ∆φ_2, I ≠ 0
Thermo-EMF occurs in a thermocouple when one of the junctions is heated.
Electrolytic dissociation. Electrolysis and its application. Faraday's laws. Electrolysis application.
Electrolytic dissociation is a solution of salts, acids and alkalis.
Electrolysis is the process of release of a substance at the cathode when an electric current passes through the electrolyte.
Application:
For the production of refined metals
Electroplating is the coating of one metal with another
Electroplating is obtaining various prints of bas-reliefs.
Faraday's laws:
m = k * I * t
The mass of the released substance at the cathode is directly proportional to the amount of electricity passed per unit of time through the electrolyte.
M / N_A * q_1 = k
k-electrochemical equivalent.
Physical meaning:
k = m / q
The electrochemical equivalent is numerically equal to the m thing that is released at the cathode after passing q_ed ^ + through the electrolyte.
SI: [k] = Kg / Cl
k = 1 / F * x; k = e * N_A-Faraday number
k ~ x
The Faraday number shows what charge is carried by a single-year ion contained in 1 mole of a substance.
F = 9.7 * 〖10〗 ^ 4 Kg / mol
Electric current in gases at atmospheric pressure. Types of discharges. Plasma concept. Electric current in rarefied gases. The concept of cathode rays. Electric current in a vacuum. Two-, three-electrode lamp. Cathode-ray tube.
Gas at P_atm = dielectric
Types of discharges:
Types of discharges:
Dependent independent
Uch. 0.1; 1.2 account 2,3
The presence of an ionizer (quiet) the presence of a high U
Sound, light
Plasma-substance is in such a state when it is generally electrically neutral, but contains equal numbers of free positive and negative charges.
It happens cold (up to 〖1000〗 ^ ° C-fire) and hot (over 1 〖million〗 ^ ° C-Sun)
Comparative characteristics of conductors, semiconductors and dielectrics. Intrinsic and impurity conductivity of semiconductors.
Electron - hole transition. Semiconductor diode. Direct and reverse inclusion of the P - H - transition.
A magnetic field. Magnetic induction. Interaction of parallel currents. The magnetic permeability of the medium. Magnetic fields of direct and circular currents and a solenoid. Ampere force. Left hand rule.
Magnetic flux. Magnetic field strength. The action of a magnetic field on a moving charge. Lorentz force. The concept of PLASMA, the prospects for its application.
Paramagnetic, diamagnetic, ferromagnetic substances. Curve of the initial magnetization of a ferromagnet. Curie point.
Electromagnetic induction. The law of electromagnetic induction. Flux linkage. The emergence of emf induction when a conductor moves in a magnetic field.
Induction current direction. Lenz's rule. Eddy currents, their use and measures to combat them.
Self-induction phenomena. Conductor inductance. The conditions on which the inductance of the conductor depends. A unit of measure for inductance.
Conditions for the occurrence of vibrations. Oscillatory motion parameters. Natural and forced oscillations. Harmonic oscillation, its equation and graph.
Propagation of vibrations in an elastic medium. Transverse and longitudinal waves. Wavelength. Mechanical resonance.
The nature of light. Wave and quantum theory of light. The speed of propagation of light in a vacuum, in various media. Determination of the speed of light by the Michelson method. Huygens' principle.
REVIEW TASKS
§ 9 Nos. 14,18,20,21,24.
§10 No. 15,20,30,41,43,48.
§ 11 Nos. 8,24,27,35,38.
§ 12 Nos. 10,31,35,52,67,75,82,101,112,129,131,136.
§ 13 Nos. 11,24,28,37,62,64.
§ 14 Nos. 13,15,17,31,41,42.
§ 17 No. 18,32,33,34.
As part of today's lesson, we will get acquainted with such a physical quantity as a charge, see examples of the transfer of charges from one body to another, learn about the division of charges into two types and about the interaction of charged bodies.
Topic: Electromagnetic phenomena
Lesson: Electrifying bodies upon contact. Interaction of charged bodies. Two kinds of charges
This lesson is an introduction to the new section "Electromagnetic phenomena", and in it we will discuss the basic concepts that are associated with it: charge, its types, electrification and the interaction of charged bodies.
The history of the concept of "electricity"
First of all, you should start by discussing the concept of electricity. In the modern world, we constantly encounter it at the everyday level and can no longer imagine our life without a computer, TV, refrigerator, electric lighting, etc. All these devices, as far as we know, work thanks to electric current and surround us everywhere. Even technologies that were not completely dependent on electricity from the beginning, such as the operation of an internal combustion engine in a car, are slowly starting to recede into history, and electric motors are actively taking their place. So where did the word "electric" come from?
The word "electric" comes from the Greek word "electron", which means "amber" (fossil resin, Fig. 1). Although it should, of course, immediately stipulate that there is no direct connection between all electrical phenomena and amber, and we will understand a little later where this association came from among ancient scientists.
The first observations of electrical phenomena date back to the 5-6th centuries BC. e. It is believed that Thales of Miletus (the ancient Greek philosopher and mathematician from Miletus, Fig. 2) first observed the electrical interaction of bodies. He conducted the following experiment: rubbed amber with fur, then brought it closer to small bodies (dust particles, shavings, or feathers) and observed that these bodies began to be attracted to amber for no reason at the time. Thales was not the only scientist who subsequently actively conducted electrical experiments with amber, which led to the emergence of the word "electron" and the concept of "electric".
Rice. 2. Thales of Miletus ()
Let's simulate similar experiments with the electrical interaction of bodies, for this we take finely cut paper, a glass rod and a sheet of paper. If you rub a glass rod on a sheet of paper, and then bring it to finely cut pieces of paper, you will see the effect of attracting small pieces to the glass rod (Fig. 3).
An interesting fact is that for the first time such a process was fully explained only in the 16th century. Then it became known that there are two types of electricity, and they interact with each other. The concept of electrical interaction appeared in the middle of the 18th century and is associated with the name of the American scientist Benjamin Franklin (Fig. 4). It was he who first introduced such a concept as an electric charge.
Rice. 4. Benjamin Franklin ()
Definition.Electric charge- a physical quantity that characterizes the magnitude of the interaction of charged bodies.
The fact that we had the opportunity to observe experimentally with the attraction of pieces of paper to an electrified stick proves the presence of forces of electrical interaction, and the magnitude of these forces is characterized by such a concept as a charge. The fact that the forces of electrical interaction can be different is easily verified experimentally, for example, by rubbing the same stick with different intensity.
To carry out the next experiment, we will need the same glass rod, a sheet of paper and a paper sultan fixed on an iron rod (Fig. 5). If you rub the stick with a sheet of paper, and then touch it to the iron rod, then the phenomenon of repulsion of the strips of the Sultan's paper from each other will be noticeable, and if you repeat the rubbing and touching several times, you will see that the effect is enhanced. The observed phenomenon is called electrification.
Rice. 5. Paper Sultan ()
Definition.Electrification- separation of electric charges as a result of close contact of two or more bodies.
Electrification can occur in several ways, the first two we have considered today:
Friction electrification;
Electrifying by touch;
Guided electrification.
Consider electrification by guidance. To do this, take a ruler and put it on the top of the iron rod, on which the paper sultan is fixed, then touch the rod to remove the charge on it, and straighten the strips of the sultan. Then we electrify the glass rod by rubbing it against the paper and bring it up to the ruler, the result will be that the ruler begins to rotate on top of the iron rod. In this case, do not touch the ruler with a glass rod. This proves that there is electrification without direct contact between bodies - electrification by guidance.
The first studies of the values of electric charges date back to a later period of history than the discovery and attempts to describe the electrical interactions of bodies. At the end of the 18th century, scientists came to the conclusion that charge division leads to two fundamentally different results, and it was decided to conditionally divide charges into two types: positive and negative. In order to be able to distinguish between these two types of charges and to determine which is positive and which is negative, we agreed to use two basic experiments: if you rub a glass rod on paper (silk), then a positive charge is formed on the rod; if you rub the ebonite stick on the fur, then a negative charge is formed on the stick (Fig. 6).
Comment.Ebonite- rubber material with a high sulfur content.
Rice. 6. Electrifying sticks with two types of charges ()
Besides the fact that the division of charges into two types was introduced, the rule of their interaction was noticed (Fig. 7):
Like charges repel;
Divergent charges attract.
Rice. 7. Interaction of charges ()
Consider the following experiment for this interaction rule. We electrify the glass rod by friction (that is, we give it a positive charge) and touch it to the rod on which the paper sultan is fixed, as a result we will see the effect that was already discussed earlier - the stripes of the sultan will begin to repel each other. Now we can explain why such a phenomenon takes place - since the stripes of the Sultan are charged positively (of the same name), they begin to repel as far as possible and form a figure in the shape of a ball. In addition, for a more visual demonstration of the repulsion of similarly charged bodies, you can bring a glass stick rubbed with paper to an electrified sultan, and it will be clearly visible how the strips of paper will deviate from the stick.
Simultaneously, two phenomena - the attraction of oppositely charged bodies and the repulsion of like charged bodies - can be observed in the following experiment. For it, you need to take a glass rod, paper and a foil sleeve, fixed with a thread on a tripod. If you rub the stick with paper and bring it to an unloaded sleeve, the sleeve will first be attracted to the stick, and after touching it, it will start to push off. This is explained by the fact that at first the sleeve, until it has a charge, will be attracted to the wand, the wand will transfer part of its charge to it, and the similarly charged sleeve will push off the wand.
Comment. However, the question remains as to why the initially unloaded sleeve is attracted to the wand. It is difficult to explain this using the knowledge available to us at the current stage of studying school physics, however, let's try, running ahead, to do this in brief. Since the sleeve is a conductor, then, once in an external electric field, the phenomenon of charge separation is observed in it. It manifests itself in the fact that free electrons in the case material move to the side that is closest to the positively charged rod. As a result, the sleeve becomes divided into two conditional areas: one is negatively charged (where there is an excess of electrons), the other is positively (where there is a lack of electrons). Since the negative region of the sleeve is located closer to the positively charged rod than its positively charged part, attraction between opposite charges will prevail and the sleeve will be attracted to the rod. After that, both bodies will acquire the same charge and repulse.
This issue is considered in more detail in the 10th grade in the topic: "Conductors and dielectrics in an external electric field."
The next lesson will discuss the principle of operation of a device such as an electroscope.
Bibliography
Homework
