§ 1 Electroscope and electrometer, principle of operation

There are instruments with which you can detect the electrification of bodies, these are an electroscope and an electrometer.

Electroscope (from Greek words“electron” and skopeo - observe, detect) - a device used to detect electrical charges.

Purpose of the device:

Charge detection;

Determination of the charge sign;

Estimating the magnitude of the charge.

An electroscope consists of a metal rod from which two easily movable strips of paper or foil are suspended. The rod is secured with an ebonite plug inside a cylindrical metal body closed with glass lids.

The operating principle of an electroscope is based on the phenomenon of electrification. When a rubbed glass rod (positively charged) touches a device (electroscope), electrical charges will flow through the rod to the leaves. Having the same sign of charge, the bodies will begin to repel, so the leaves of the electroscope will diverge at a certain angle. The consumption of leaves at an angle of a larger value occurs when a larger charge is imparted to the electroscope, and therefore leads to an increase in the repulsive force between the bodies (Fig.). Consequently, by the angle of divergence of the leaves, you can find out about the amount of charge of the electroscope. If we bring a body whose charge is negative to a device charged positively, we will notice that the angle between the leaves will decrease. Conclusion: an electroscope makes it possible to find out the sign of the charge of the body under study.

In addition to the electroscope, one more device can be distinguished - an electrometer. The operating principles of the devices are practically the same. The electrometer has a light aluminum pointer, with the help of which, by the angle of deflection, you can find out the amount of charge that was imparted to the electrometer rod.

§ 2 Electric field and its characteristics

Bodies are electrified in the following way: they are given a positive or negative charge, increasing or decreasing the amount of charge. In this case, bodies acquire different properties and are able to attract or repel other bodies. How does a body “understand” that the charge of another must be attracted or repelled? To answer this question, you need to find out a special form of matter - the “electric field”.

Let's electrify a metal ball on a plastic stand and a light cork ball on a thread with the same name (of the same sign) (let's call it a test ball). We will transfer it to various points space around a large ball. We will notice that at every point in space around the electrified body a force is detected acting on the test ball. We can see that it exists by the deflection of the ball thread. As the ball moves away from the test ball, the ball on the string deflects less, therefore, the force acting on it becomes less and less (according to the angle of deviation of the string from the equilibrium position).

So, at every point in space around electrified or magnetized bodies there is a so-called force field that can influence other bodies.

An electric field is a special type of matter created by an electrically stationary charge and acting with some force on a free charge placed in this field.

Field characteristics:

1. It is material, since it acts on material objects (light free body- sleeve).

2. It is real, since it exists everywhere and even in a vacuum (airless space) and independently of a person.

3. Invisible and does not affect human senses.

4. Does not have a specific size, border, shape.

5. Occupies all the space surrounding a given charged body.

6. As you move away from the charge, the field weakens.

7. Has energy.

8. Electric fields have two principles: the principle of independence (if there are several fields, then each field exists independently of the other), the principle of superposition (overlay) - the fields do not distort each other.

9. There are particles around a charged body. Any charged body has its own electric field around it.

10. A field is detected by the influence of a certain force on a freely suspended charged body; this force is called electric.

§ 3 Power lines electric field

To graphically represent the field and find out its direction of propagation, it is necessary to use the field line method.

To do this, let's conduct an experiment.

Let's take two metal balls on plastic stands, as well as a needle, also mounted on a stand. Place the balls at a distance of 40-50 cm from each other, and between them - a stand with a needle. Balance a dry wood sliver on it. As you can see, the balls have different signs of charges, we will see that the sliver will turn around so that it is on the straight line connecting the balls (see the upper part of the figure).

If we place the sliver in different positions near the balls (see figure), we will notice that it will take a position on the mentally drawn arc-shaped lines connecting the balls; This is exactly what electric field lines look like.

Let us demonstrate an interesting case: there are charged bodies. Place glass over them, and sprinkle finely chopped hairs on the surface of the glass. Under the influence of the field, they begin to orient themselves in an interesting way, and a “picture” appears showing the location of the bodies. (see pictures below). On the left and right they are oriented around positively and negatively charged particles, and in the central part - around oppositely charged balls.

Lines of force are depicted as more “frequent” lines where a larger electric charge is detected, and therefore a greater electrical force when a given field influences the body. The field line model shows the magnitude of the force and the direction of action of the field on bodies and particles placed in the field.

There is a device with which you can find out the magnitude and sign of the charge, which is important in electrical phenomena. Also, the electric field is “related” to the charge. When a charge moves in the other direction, the field instantly follows it.

List of used literature:

1. Physics. 8th grade: Textbook for general education institutions/A.V. Peryshkin. – M.: Bustard, 2010.
2. Physics 7-9. Textbook. I.V. Krivchenko.
3. Physics. Directory. O.F. Kabardin. - M.:AST-PRESS, 2010.

Slide 2

Electroscope

After the lesson the student knows:

• The structure and purpose of an electroscope (electrometer).
• Concepts of electric field, electric forces.
• Conductors and dielectrics.

• Identify and systematize the knowledge they have about the electrification of bodies.
• Explain the effect of an electric field on an electric charge introduced into it.
• Deepens knowledge about the electrification of bodies.
• Develops intellectual skills.

Lesson structure:

1. Organizational stage.
2. Repetition to update previous knowledge.
3. Formation of new knowledge.
4. Consolidation, including the application of new knowledge in a changed situation.
5. Homework.
6. Summing up the lesson.

1. Electroscope (1 copy).
2. Electrometer (2 copies), metal conductor, ball.
3. Electrophoric machine.
4. "Sultans".
5. Glass and ebonite stick; (wool, silk).
6. Presentation.

Lesson summary “Electric field. Electroscope"

Purpose of the lesson: to introduce students to the structure of the electroscope. To form ideas about the electric field and its properties.

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

Lesson progress:

1. Organizational moment

2. Updating knowledge of students

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

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

While two students read the instructions for performing the experiment, I offer the following questions to the attention of the rest:

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

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

3. How do bodies with like 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: “Friction creates charges?” Why?

7. Is it possible to electrify a brass rod by holding it in your hand?

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

9. Name substances that are conductors.

10. Name substances that are dielectrics.

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

Students demonstrate experiments and draw conclusions. And the result is immediately assessed.

3. Learning new material.

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

Is there another way to determine whether a body is charged: using a device such as an electroscope?

Two 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 an electric field.

The name “electroscope” comes from the Greek words “electron” - electricity and “skopeo” - observe, detect. (write in a notebook)

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

See what changes will happen when I bring the charged

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

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

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

Experience: Charge the sleeve “negatively”, the stick “positively” and bring the sticks to the sleeve. And watch how the cartridge case is attracted to the stick as it approaches.

The main property of the 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 effect of the field is stronger, and when moving away from them the field weakens.

Children making an electroscope from available materials: a plastic cup, a 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 learn about in class?

What property of the electric field have you learned?

Does the electric field act equally at any distance from a charged body?

5 D/z §27.28.

Instruction 1

1. Take two balls

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

3. Using tape, attach one of the balls to the tripod.

4. Rub the hanging ball with a piece of wool. It is necessary to make at least 20 movements with a piece of fabric back and forth. Release 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 ball close enough to the first so that they seem to fly apart

INSTRUCTIONS2

1.Take a piece of nylon fabric

2.Fold the plastic bag in half and take 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 remove the package?

T E S T

on the topic “Interaction of charged bodies”

1. When glass rubs against silk, it charges

B – positive D – negative

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

A – positive E – negative

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

Which pair of balls is not charged?

S – first U – second R – third

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

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 figure).

Which pair of balls has different charges?

K – first O – second L – third

AMPERE (Ampere) Andre Marie (1775 - 1836), an outstanding French scientist, physicist, mathematician and chemist, in whose honor one of the basic electrical quantities is named - the unit of current - 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.

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

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

James Clerk Maxwell (1831-79) - English physicist, creator of classical electrodynamics, one of the founders statistical physics, predicted the existence electromagnetic waves, put forward the idea of ​​​​the electromagnetic nature of light, established the first statistical law - the law of the distribution of molecules by speed, 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, and put forward the idea of ​​​​the electromagnetic nature of light. Established a statistical distribution named after him. He studied the viscosity, diffusion and thermal conductivity of gases. Maxwell showed that the rings of Saturn consist of separate bodies.