Lesson summary "Electric field. Electroscope"

The purpose of the lesson: to acquaint students with the device of the electroscope. Form ideas about the electric field and its properties.

Equipment: an electroscope, a tube on a thread on a stand, an ebonite, glass rod, balloons, a piece of nylon cloth, scissors, tape, woolen cloth, plastic cups, paper clips, foil.

During the classes:

1. Organizing time

2. Updating knowledge of students

For some of you, today's lesson will start with test items... (5 people), those who have tests can start working, time is limited, after 3 minutes, we will check the correctness of the execution.

There are balloons on the display table. Two students are called to the demonstration table. The task of the students is to lead an experiment and draw a conclusion about the interaction of electrified bodies.

While two students are reading the instructions for performing the experiment, I present the following questions for the others' attention:

1. How to transfer an electric charge from one body to another?

2. What two types of charges exist in nature, as they are called?

3. How do bodies with the same charges interact with each other?

4. How do bodies with opposite charges interact with each other?

5. Is it possible to charge only one of the contacting bodies during electrification by friction?

6. Is the expression correct: "When friction creates charges?" Why?

7. Can you electrify a brass rod by holding it in your hand?

8. Is it possible to obtain simultaneously opposite charges at the ends of a glass rod?

9. Name the substances that are conductors.

10. Name the substances that are dielectrics.

Checking the execution of test tasks. The key to the test is the word "True."

Experiments are demonstrated by students and conclusions are drawn. And the result is immediately evaluated.

3. Learning new material.

- Tell me how to determine if the body is electrified?

There is another way to determine whether a body is charged: with the help of a device such as an electroscope?

Two air balloon hang without touching each other, but nevertheless it is visible

that they interact, repel each other. When towing

from one car to another, the interaction of cars is carried out through a cable. And the interaction between charged bodies is carried out using electric field.

The name "electroscope" comes from the Greek words "electron" - electricity and "scapeo" - to observe, to detect. (Writing in a notebook)

What does it consist of? A metal rod passes through a plastic stopper in a metal frame, at the end of which two sheets of tissue paper are fixed. The frame is covered with glass on both sides.

See what changes will happen when I bring the charged

Stick. (The leaves will deviate). That is, by the deviation of the leaves, one can judge whether the body is charged. Another device is used for experiments.

Electrometer. Here, a light metal arrow is charged from a metal rod, pushing off from it is not the greater the angle, the more they are charged.

According to the teachings of the English physicists Faraday and Maxwell, around charged bodies. The mediator in this interaction is the electric field. The electric field is the form of matter, through which it is carried out electrical interaction charged bodies, it surrounds any charged body and manifests itself in action on a charged body.

Experience: Load the sleeve "negatively", the stick "positively" and bring the sticks to the sleeve. And watch how the sleeve is attracted to the stick as it approaches.

The main property of an electric field is its ability to act on an electric charge with some force.

The force with which the electric field acts on the charge introduced into it is called electric force.

Near charged bodies, the action of the field is stronger, and with distance from them, the field weakens.

Making an electroscope by children from improvised means: a plastic cup, paper clip, foil, plasticine.

4 Summing up the lesson.

What is an electroscope for and what parts does it consist of?

What concept did you meet in the lesson?

What property of the electric field have you learned?

Does the electric field act in the same way at any distance from a charged body?

5 D / s §27.28.

Instruction 1

1. Take two balls

2. Tie each ball with a thread 30 cm long.

3.Use adhesive tape to attach one of the balls to the tripod.

4. Rub the hanging ball with a piece of wool. Must be done by at least 20 back and forth movements with a piece of cloth. Let go of the ball and it will hang freely

5. Rub the second ball with a piece of wool. Take it by the end of the thread and bring it to the first ball. What will happen to the balls?

6.Attach the second balloon close enough to the first so that it looks like they are flying apart

INSTRUCTION2

1. Take a piece of nylon cloth

2.Fold the plastic bag in half and hold it in your hand

3.Place a piece of nylon fabric between these halves and run the bag over the nylon several times

4.What happens when you put the bag away?

T E S T

on the topic "Interaction of charged bodies"

1. Glass is charged when rubbed against silk

B - positive G - negative

2. If an electrified body is repelled by an ebony stick rubbed on fur, then it is charged ...

A - positive E - negative

3. Three pairs of light balls are suspended on threads (see fig.).

Which pair of balls is not charged?

C - first Y - second R - third

4. Three pairs of light balls are suspended on threads (see fig.).

Which pair of balls has the same charges?

N - first P - second R - third

5. Three pairs of light balls are suspended on threads (see fig.).

Which pair of balls has different charges?

K - first O - second L - third

AMPERE (Ampere) André Marie (1775 - 1836), an outstanding French scientist, physicist, mathematician and chemist, after whom one of the main electrical quantities is named - the unit of current - the ampere. The author of the very term "electrodynamics" as the name of the doctrine of electricity and magnetism, one of the founders of this doctrine.

Coulomb Charles Augustin (1736-1806), French engineer and physicist, one of the founders of electrostatics. He investigated the twisting deformation of threads, established its laws. Invented (1784) the torsion balance and discovered (1785) the law named after him. Established the laws of dry friction.

Faraday (Faraday) Michael (22.9.1791 - 25.8.1867), English physicist and chemist, the founder of the doctrine of the electromagnetic field, a member of the Royal Society of London (1824).

James Clerk Maxwell (1831-79) - English physicist, creator of classical electrodynamics, one of the founders of statistical physics, predicted the existence of electromagnetic waves, put forward the idea of ​​the electromagnetic nature of light, established the first statistical law - the law of molecular velocity distribution, named after him. Developing the ideas of Michael Faraday, he created a theory electromagnetic field(Maxwell's equations); introduced the concept of displacement current, predicted the existence of electromagnetic waves, put forward the idea of ​​the electromagnetic nature of light. Established a statistical distribution named after him. Investigated the viscosity, diffusion and thermal conductivity of gases. Maxwell showed that Saturn's rings are composed of separate bodies.

Lesson for 8th grade students.

The purpose of the lesson:

To acquaint children with the new device and its purpose;

Give the concept of conductors and non-conductors of electricity;

Education of discipline, accuracy of writing in a notebook, attentiveness.

Formation of a scientific worldview: the world is cognizable, natural phenomena obey physical laws.

Development of thinking and memory;

Ability to speak correctly.

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8th grade.

Electroscope. Conductors and non-conductors of electricity. Electric field.

The purpose of the lesson:

To acquaint children with the new device and its purpose;

Give the concept of conductors and non-conductors of electricity;

Education of discipline, accuracy of writing in a notebook, attentiveness.

Formation of a scientific worldview: the world is cognizable, natural phenomena obey physical laws.

Development of thinking and memory;

Ability to speak correctly.

Tasks:

Educational:to reveal the property of substances - electrical conductivity; familiarize with the use of conductors and dielectrics in practice; to reveal the principle of operation of the electroscope.

Educational: creation of situations of independent search for solutions to the assigned tasks; fostering a respectful attitude towards the opinion of another person.

Developing: development logical thinking; development of cognitive interest.

Lesson form: work with the text of the textbook, group forms: work

(in pairs), independent work, an experimental study.

Teaching method: system search.

Lesson location: intermediate: the lesson can be conducted after studying the concept of "electric charge" and the interaction of electric charges.

Equipment for the lesson:

1 demonstration electrometer, glass and ebonite sticks, a set of minerals, a computer, a multimedia projector.

A single collection of digital educational resources (http://school-collection.edu.ru/)

Video "How to set the sign of the electroscope charge"

Video "Negative charge of the electrometer"

Lesson plan.

1. Organizing time.
2. Knowledge update.
3. Historical excursion.
4. Learning new material.
5. Consolidation of knowledge.
6. Learning new material.
7. Consolidation and correction of knowledge.
8. Lesson summary, homework.

During the classes:

1. Organizational moment.

Greetings, readiness for the lesson.

2. Actualization of knowledge.

In the last lesson, you and I studied the topic: “Electrification of bodies upon contact. Interaction of charged bodies. Two kinds of charges. At home, you had to repeat it.

(slide 1)

1. What can be said about a body if it attracts other bodies?

A body that can attract other bodies is said to be electrified.

2. What else do they say about the body, if it is electrified?

That the body is given an electric charge.

3. How many bodies can participate in electrification?

Only two bodies can participate in electrification.

4. Is it possible to transfer an electric charge from one body to another, if so how?

An electrical charge can be transferred from one body to another by touching a charged body to an uncharged one.

5. Are bodies with charges of the same kind attracted or repelled?

Bodies with charges of the same kind repel.

6. Are bodies with charges of different kinds attracted or repelled?

Bodies with charges of the same kind attract.

7. How many kinds of electric charges do you know?

There are only two kinds of charges.

8. Name them.

Positive and negative

9. How do charges mean in diagrams, drawings and drawings?

The positive sign "+" and the negative sign "-".

Verification work.

Individual work in the form of a test. It is performed in writing on small format sheets.

3. Learning new material.

Today in the lesson we will get acquainted with the electroscope, its purpose and device, as well as with conductors and non-conductors of electricity.

(slide 2)

“Write the number and topic of the lesson” (written on the chalkboard).

So, we already know that electrified bodies are attracted or repelled, by the interaction it is possible to judge whether an electric charge is imparted to the body. Therefore, the device design, with the help of which it is determined whether the body is electrified, is based on the interaction of charged bodies. (An electroscope is placed on the table) This device is called electroscope , from Greek words ELECTRON , you know how this word is translated from a vulgar lecture, and with cope about - to observe, to discover.

(slide 3)

Write this definition in a notebook.

I have a school electroscope on my desk, look closely at it through a plastic stopper inserted into a metal frame, a metal rod is passed, at the end of which there are two sheets of thin paper, the frame is covered with glass on all sides. Write in a notebook thatan electroscope consists of:

1. Plastic cork;

2. Metal frame;

3. Metal bar;

4. Two pieces of thin paper;

5. Two glasses.

(I lightly rub the ebony stick on the fur and touch it to the metal rod of the electroscope.)

1. Look, the petals of the electroscope have spread out at a certain angle.

(I rub the ebony stick harder on the fur and touch it to the metal rod of the electroscope without discharging it.)

2. Look, the petals of the electroscope have diverged to a greater angle.

Hence, we can conclude thatby the change in the angle of divergence of the leaves of the electroscope, one can judge whether its charge has increased or decreased.

(slide 4)

We have considered with you one of the types of electroscope, where the leaves are the indicator of the electrification of the body. There is another type of electroscope, where the indicator of the electrification of the body is a light metal arrow. In it, the arrow deviates at a certain angle from the charged metal rod.

Now I will touch the electroscope with my hand. Let's see what happens to the petals. (I touch the rod of the electroscope with my hand.) Look, the petals of the electroscope have dropped, so it is discharged.

This will happen with any charged body that we touch. Electric charges will transfer to our body and through it can go into the ground. A charged body will also be discharged if it is connected to the ground with a metal object, for example, an iron or copper wire.

Let's see this by experience:

(slide 5)

1. Take two electroscope. One is charged and the other is not, I connect them with an iron rod. Note that the charge from a charged electroscope flows to an uncharged one.

(slide 6)

2. Also take two electroscope. One is charged and the other is not, I connect them with a long glass rod. Please note that the charge from a charged electroscope does not flow to an uncharged one.

(slide 7)

Conclusion: so, from our experiment, we can conclude that, according to the ability to conduct electric charges, substances are conventionally divided into conductors and non-conductors of electricity. All metals, soil, solutions of salts and acids in water are good conductors of electricity.

Non-conductors of electricity, or dielectrics, include porcelain, ebonite, glass, amber, rubber, silk, nylon, plastics, kerosene, air (gases).

Bodies made of dielectrics are called isolators , from the Greek word isolro - to retire.

5. Primary consolidation of knowledge.

We fill in the table.

(slide 8)

metals, soil, porcelain, ebonite, glass,

salt solutions, amber, rubber, silk,

acids in water nylon, plastics

kerosene, air (gases).

6. The stage of obtaining new knowledge.

The study of the new material is carried out on the basis of a demonstration experiment with two electrometers (electroscopes), on the rods of which there are identical spherical conductors, and on the analysis of its results. I charge one of two identical electrometers and ask the students to answer the question: "What happens if you connect these electrometers with a glass rod?" The answers are verified by experience, which shows that no change occurs. This confirms that glass is a dielectric.

If you use a metal rod to connect electrometers, holding it by a handle that does not conduct electricity, then the initial charge will be divided into two equal parts: half of the charge will go from the first conductor to the second.

We hang a charged sleeve on the threads and bring an electrified glass rod to it. The sleeve will deviate from the vertical position, being attracted to the stick. Consequently, charged bodies are able to interact with each other at a distance. How is the action transferred from one of these bodies to another? Maybe it's all about the air between them? Let us find out by experience. Place the charged electroscope (with the glasses removed) under the bell of the air pump, and then pump out the air from under it. We see that in airless space the leaves of the electroscope are still repelled from each other. This means that air does not participate in the transmission of electrical interaction. Then by what means is the interaction of charged bodies carried out?

The answer to this question was given in their works by the English scientists M. Faraday (1791 - 1867) and J. Maxwell (1831 - 1879), who proved that the "agent" transmitting the interaction is an electric field.

(slide 9)

An electric field is a form of matter through which the electric interaction of charged bodies is carried out. It surrounds any charged body and manifests itself by acting on a charged body.

After that, relying on simple experiments the mainelectric field properties:

1. The electric field of a charged body acts with some force on any other charged body that finds itself in this field. This is evidenced by all experiments on the interaction of charged bodies. So, a negatively charged sleeve, which finds itself in the electric field of a positively electrified rod, is subjected to the action of the force of attraction to it.
2. The field generated by them is stronger near charged bodies, and weaker at a distance.

An electric field is depicted graphically using magnetic lines of force.

(slide 10)

Magnetic field image

1. The stage of generalization and consolidation of new material.

(slide 11)

1. Guys, please tell me what the electroscope is for?

An electroscope is a device used to find out whether a body is electrified or not.

2. What are the main parts of the electroscope?

The electroscope consists of: a plastic plug; metal frame; metal rod; two pieces of thin paper; two glasses.

3. What can be said by looking at the change in the angle of divergence of the electroscope leaves?

By changing the angle of divergence of the leaves of the electroscope, one can judge whether its charge has increased or decreased.

4. In what two groups are substances divided according to their ability to conduct electric current?

All substances are conventionally divided into conductors and non-conductors of electricity.

5. What is another name for non-conductors of electricity?

Dielectrics.

6. Give examples of dielectrics.

Non-conductors of electricity include porcelain, ebonite, glass, amber, rubber, silk, nylon, plastics, kerosene, air (gases).

7. What are the substances that belong to the conductors?

All metals, soil, solutions of salts and acids in water.

DO YOU KNOW?

Strong electric fields operate in our atmosphere. The earth is usually negatively charged,
and the bottom of the clouds is positive. The air we breathe contains charged particles - ions. The content of ions in the air varies depending on the season, the purity of the atmosphere and the meteorological conditions. The entire atmosphere is permeated by these particles, which are in continuous motion, with either positive or negative ions prevailing. As a rule, only positive ions have a negative effect on human health. Their large predominance in the atmosphere causes unpleasant sensations.

The fly larvae move in the direction of the lines of force of the induced electric field. It is used by removing them from edible products.

Bushes and trees are a powerful shield that keeps the electric water from entering.

"LIVE" ELECTRICITY

The first mention of electric fish dates back more than 5000 years ago. Ancient Egyptian tombs depict African electric catfish.

(slide 12)

The Egyptians believed that this catfish is a "protector of fish" - a fisherman pulling out a net with fish could receive a decent electrical discharge and release the net from his hands, releasing all the caught catch back into the river.

"Electric" vision of fish.

Fish use electrical organs to detect foreign objects in the water. Some fish generate electrical impulses all the time. Around their bodies in water flow electric currents... If a foreign object is placed in the water, then the electric field is distorted and the electrical signals arriving at the sensitive electroreceptors of the fish change. The brain compares signals from many receptors and forms in fish an idea of ​​the size, shape and speed of the object.

The most famous electric hunters are stingrays ... The stingray swims onto the victim from above and paralyzes it with a series of electrical discharges. However, its "batteries" are depleted and it takes some time to recharge.

The strongest electrical discharge is possessed by freshwater fish calledelectric eels... Young 2-centimeter fish cause a slight tingling sensation, and adults that reach two meters in length are capable of generating 550 volt discharges with a current of 2 amperes more than 150 times per hour. HaveSouth American eeldischarge voltage can reach 800 V.

The ancient Greeks and Romans (500 BC-500 AD) knew about the electric ray. ... Pliny in 113 AD described how a stingray uses "magical power" to immobilize its prey. The Greeks knew that "magical power" could be transmitted through metal objects, such as spears, with which they hunted fish.

Never pick up the stingrays. If you are hunting fish with a harpoon, be careful not to hit the electro-skate - removing the weapon from its body, you will not experience the most pleasant sensations. If the electric skate is caught in a trawl or net, you need to take it with your hands in thick rubber gloves or with a special hook with an insulated handle.

Live clock.
African fish gymnarche sends to environment electrical signals, the duration of which is so precise and periodic that it can be compared to a crystal oscillator. The French engineer A. Florion processed the signals emitted by the fish, and received an original "fish" bioelectric clock. They can "walk" for 15 years, you just need to feed the fish every day.

Fish with electric organs (sharks and rays) are able to detect prey by the work of its heart, in this case, an electric field is recorded, which creates a beating heart of the prey fish.

Electric fish.

Some fish, trying to escape, burrow into the sand and freeze there. But they also have no chance, because while they are alive, their bodies generate electric fields, which are captured, for example, by its unusual head a hammerhead shark, rushing, as it seems, directly onto empty ground and pulling out a beating prey from it.

Stingrays can detect crabs they love by their electric fields, and catfish can even detect electric fields created by worms buried in the ground. A shark, reacting to an electric field, can also very accurately attack a flounder buried in the sand.

The electric organs of sharks and rays are very sensitive: fish react to e-mail. fields with a strength of 0.1 μV / cm.

Electric fish use electrical signals to communicate with each other. They notify other individuals that the area is occupied or that they have found food. There are electrical signals: "challenge" or "surrender." All these signals are well received by fish at a distance of about 10 meters.

1. Summarizing. Homework.

So, today in the lesson you got acquainted with the electroscope, its purpose and device, with conductors and non-conductors of electricity, got acquainted with the concept of an electric field, and also repeated the previously studied material and consolidated a new one. Those who actively worked in the lesson, answering the questions, received appropriate marks. Thanks to all! Goodbye!"

1. §§ 27.28
2. Make an electroscope at home.

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If you walked around in clothes made of synthetic fabric, then it is very likely that soon you will feel not very pleasant consequences from such an activity. Your body becomes electrified, and when you greet a friend or touch the doorknob, you will feel a sharp current.

It is neither fatal nor dangerous, but not very pleasant. Everyone at least once in their life has come across a similar phenomenon. But often we find out that we are electrified, already by the consequences. Is it possible to know that the body is electrified in some nicer way than a shot of current? Can.

What is an electroscope and an electrometer for?

The simplest device for determining electrification is an electroscope. Its principle of operation is very simple. If you touch the electroscope with a body that has some kind of charge, then this charge is transferred to a metal rod with petals inside the electroscope. The petals will acquire a charge of the same sign and disperse, repelled by the same charge from each other. The scale will show the size of the charge in pendants. There is also a kind of electroscope - an electrometer. Instead of petals, an arrow is fixed in it on a metal rod. But the principle of operation is the same - the rod and the arrow are charged and repelled from each other. The amount of deviation of the arrow shows the charge level on the scale.

Division of electrical charge

The question arises - if the charge can be different, then there is some value of the smallest charge that cannot be divided? After all, you can reduce the charge. For example, by connecting a charged and uncharged electroscope with a wire, we will divide the charge equally, which we will see on both scales. Having discharged one electroscope by hand, we again divide the charge. And so on until the value of the charge becomes less than the minimum division of the electroscope scale. Applying devices for a finer measurement, it was possible to establish that the division electric charge not endlessly. The smallest charge is denoted by the letter e and is called the elementary charge. e = 0.00000000000000000016 C = 1.6 * (10) ^ (- 19) C (Coulomb). This value is billions of times less than the amount of charge we get when we electrify our hair with a comb.

The essence of the electric field

Another question that arises when studying the phenomenon of electrification is as follows. To transfer a charge, we need to touch another body directly with an electrified body, but for the charge to act on another body, direct contact is not needed. Thus, an electrified glass rod attracts pieces of paper from a distance without touching them. Maybe this attraction is transmitted through the air? But experiments show that the effect of attraction remains in airless space. What is it then?

This phenomenon is explained by the existence of a certain type of matter around charged bodies - an electric field. The electric field in the course of physics of the 8th grade is given the following definition: an electric field is a special kind of matter, different from matter, existing around each electric charge and capable of acting on other charges. To be honest, there is still no definite answer what it is and what are its reasons. Everything that we know about the electric field and its effects has been established empirically. But science is moving forward, and I want to believe that this issue will someday be resolved to complete clarity. Moreover, although we do not fully understand the nature of the existence of an electric field, nevertheless, we have already learned quite well how to use this phenomenon for the benefit of mankind.

Slide 2

Electroscope