Presentation electroscope conductors and dielectrics electric field. Presentation on the topic "electroscope electric field"

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matter substance field solid state liquid state gaseous state plasma electric magnetic gravitational nuclear

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Comparison of field and substance properties

substance 1. Impenetrable 2. Has volume and shape 3. Field is felt visually and tactilely 1. Mutually permeable 2. Not limited in space 3. Not perceived by the senses

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Electric field properties

1. Exists around charged bodies 2. Invisibly, determined by the action and with the help of instruments 3. Depicted using lines of force 4. The lines indicate the direction of the force acting from the field on a positively charged particle placed in it.

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What charge do the balls have?

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Count...

How many excess electrons are contained in a body with a charge of 4.8 10-16 C? Identical metal balls with charges -7q and 11q were brought into contact and moved apart to the same distance. What are the charges of the balls? 3. If the body lacks five electrons, then what is the sign and charge module on it?

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Check yourself:

1. Identical metal balls with a charge of 7e and 15e were brought into contact, then moved apart to the same distance. What was the charge of the balls? 2. Is it possible to say that the charge of the system is the sum of the charges of the bodies included in this system? 3. What is the name of the process leading to the appearance of charges on the body? 4. What is the structure of Rutherford's atom?

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5. If the body is electrically neutral, does this mean that it does not contain electric charges? 6. If the number of charges in a closed system has decreased, does this mean that the charge of the entire system has decreased? 7. How do opposite charges interact? 8. How many types of charges does a gold atom contain? 9. What is the structure of the Thomson atom?

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§ 1 Electroscope and electrometer, principle of operation

There are devices with which you can detect the electrification of bodies, this is an electroscope and an electrometer.

An electroscope (from the Greek words "electron" and skopeo - to observe, detect) is a device used to detect electric charges.

Purpose of the device:

charge detection;

Determining the sign of the charge;

Estimating the magnitude of the charge.

An electroscope consists of a metal rod to which two easily movable strips of paper or foil are suspended. The rod is fixed with an ebonite plug inside a cylindrical metal case, closed with glass covers.

The principle of operation of the electroscope is based on the phenomenon of electrification. When a rubbed glass rod (positively charged) comes into contact with a device (electroscope), electric charges will flow through the rod to the leaves. Having the same charge sign, the bodies will start 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, which means it leads to an increase in the repulsive force between the bodies (Fig.). Therefore, by the angle of divergence of the leaves, you can find out about the magnitude of the charge of the electroscope. If a body with a negative charge is brought to a device that is positively charged, we will notice that the angle between the leaves will decrease. Conclusion: the electroscope makes it possible to find out the sign of the charge of the investigated body.

In addition to the electroscope, one more device can be distinguished - an electrometer. The principle of operation of the devices is practically the same. The electrometer has a light aluminum pointer, with the help of which, by the angle of deviation, one can find out the amount of charge that has been imparted to the electrometer rod.

§ 2 Electric field and its characteristics

Bodies are electrified as follows: they transfer a positive or negative charge to them, increasing or decreasing the magnitude of the charge. In this case, bodies acquire different properties and are able to attract or repel other bodies. How does the 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 with the same name (of the same sign) a metal ball on a plastic stand and a light cork ball on a thread (let's call it a test ball). We will move it to different points in space around a large ball. We will notice that at every point in space around an electrified body, a force is found acting on the test ball. The fact that it exists is observed by the deviation of the ball thread. As the ball moves away from the trial ball, the ball on the thread deviates less, therefore, the force acting on it becomes less and less (by the angle of deviation of the thread from the equilibrium position).

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

An electric field is a special kind of matter created by an electrically resting 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 (a light free body - a sleeve).

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

3. Invisibly and does not affect the 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. Possesses energy.

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

9. There is about a charged body, particles. Every charged body has its own electric field around it.

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

§ 3 Electric field lines

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 do an experiment.

Let's take two metal balls on plastic stands, as well as a needle, also mounted on a stand. We place the balls at a distance of 40-50 cm from each other, and between them - a stand with a needle. We balance a dry wooden chip on it. As you can see, the balls have different charge signs, we will see that the sliver will turn around so as to be on the straight line connecting the balls (see the top of the figure).

If we place a chip in different positions near the balls (see Fig.), we note that it will take a position on the mentally drawn arcuate lines connecting the balls; this is what the electric field lines look like.

Let's demonstrate an interesting case: there are charged bodies. We place glass above them, and pour finely chopped hairs on the surface of the glass. Under the action of the field, they begin to orient themselves in an interesting way, a “picture” appears showing the location of the bodies. (see pictures below). Left and right, they are oriented around positively and negatively charged particles, and in the central part - around oppositely charged balls.

The lines of force are depicted as more “frequent” lines where a larger electric charge is found, and hence a large electric force when a given field is applied to a body. The model of lines of force shows the magnitude of the force and the direction of the field on 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 "connected" to the charge. When the charge moves in the other direction, the field instantly follows it.

List of used literature:

1. Physics. Grade 8: Textbook for educational 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.

Electroscope(from the Greek words "electron" and skopeo - to observe, detect) - a device for detecting electric charges. An electroscope consists of a metal rod from which two strips of paper or aluminum foil are suspended. The rod is reinforced with an ebonite cork inside a cylindrical metal case, closed with glass covers.

The device of the electroscope is based on the phenomenon of electric repulsion of charged bodies. When a charged body, such as a rubbed glass rod, comes into contact with the rod of an electroscope, electric charges are distributed over the rod and leaves. Since similarly charged bodies repel each other, under the action of the repulsive force, the leaves of the electroscope will diverge at a certain angle. Moreover, the greater the charge of the electroscope, the greater the repulsive force of the leaves and the greater the angle they will disperse. Therefore, according to the angle of divergence of the leaves of the electroscope, one can judge the magnitude of the charge on the electroscope.

If a body charged with the opposite sign, for example, negatively, is brought to a charged electroscope, then the angle between its leaves will begin to decrease. Therefore, the electroscope allows you to determine the sign of the charge of an electrified body.

It is also used to detect and measure electric charges. electrometer. Its principle of operation is not significantly different from the electroscope. The main part of the electrometer is a lightweight aluminum needle that can rotate around a vertical axis. By the angle of deviation of the electrometer needle, one can judge the amount of charge transferred to the electrometer rod.

Properties of an electric field 1. Exists around charged bodies 2. Invisibly, determined by the action and with the help of instruments 3. Depicted using lines of force 4. The lines indicate the direction of the force acting from the field on a positively charged particle placed in it.

Calculate ... How many excess electrons are contained in a body with a charge of 4.8 10-16 C? Identical metal balls with charges -7q and 11q were brought into contact and moved apart to the same distance. What are the charges of the balls? 3. If the body lacks five electrons, then what is the sign and charge module on it?

Check yourself: 1. Identical metal balls with a charge of 7e and 15e brought into contact, then moved apart to the same distance. What was the charge of the balls? 2. Is it possible to say that the charge of the system is the sum of the charges of the bodies included in this system? 3. What is the name of the process leading to the appearance of charges on the body? 4. What is the structure of Rutherford's atom?

5. If the body is electrically neutral, does this mean that it does not contain electric charges? 5. If the body is electrically neutral, does this mean that it does not contain electric charges? 6. If the number of charges in a closed system has decreased, does this mean that the charge of the entire system has decreased? 7. How do opposite charges interact? 8. How many types of charges does a gold atom contain? 9. What is the structure of the Thomson atom?

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

It's not fatal or dangerous, but it's not very pleasant. Everyone has experienced something like this at least once in their life. 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 more pleasant way than an injection of current? Can.

What is an electroscope and an electrometer?

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 will be 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 charge of the same sign from each other. On the scale you can see the size of the charge in pendants. Another type of electroscope is the electrometer. Instead of petals on a metal rod, an arrow is fixed in it. But the principle of action is the same - the rod and the arrow are charged and repel each other. The amount of deflection of the arrow indicates the level of charge on the scale.

Division of electric 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. Using instruments for more subtle measurements, it was possible to establish that the division of electric charge is not infinite. The value of the smallest charge is denoted by the letter e and is called the elementary charge. e=0.000000000000000000016 Cl=1.6*(10)^(-19) Cl (Coulomb). This value is billions of times less than the amount of charge that we get by electrifying the hair with a comb.

The essence of the electric field

Another question that arises when studying the phenomenon of electrification is as follows. In order to transfer the charge, we need to directly touch the electrified body to another body, but in order for the charge to act on another body, direct contact is not needed. So, an electrified glass rod attracts pieces of paper to itself at a distance, without touching them. Maybe this attraction is transmitted through the air? But experiments show that in an airless space the effect of attraction remains. 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 8th grade physics course is given the following definition: an electric field is a special kind of matter, different from matter, that exists around each electric charge and is capable of acting on other charges. To be honest, there is still no clear answer what it is, and what are its causes. Everything 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.