Properties of an electric field 1. Exists around charged bodies 2. Invisible, determined by action and with the help of devices 3. Depicted with the help of lines of force 4. Lines indicate the direction of the action of the force acting from the side of 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 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 the modulus of charge on it?
Check yourself: 1. Identical metal balls with a charge of 7th and 15th were brought into contact, then moved apart to the same distance. What is the charge of the balls? 2. Can we say that the charge of a system is the sum of the charges of 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 in a closed system the number of charges has decreased, does this mean that the charge of the entire system has decreased? 7.How do opposite charges interact? 8. How many kinds of charges does a gold atom contain? 9. What is the structure of Thomson's atom?
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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 some quizzes. (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 balloons hang without touching each other, but you can still see
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 "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. 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.
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. Make at least 20 back and forth movements with the 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
Lesson objectives: To get acquainted with the device of the electroscope. Get to know the device of the electroscope. Introduce the concepts of conductors and dielectrics. Introduce the concepts of conductors and dielectrics. Form an idea of the electric field and its properties. Form an idea of the electric field and its properties. Be convinced of the reality of the existence of an electric field on the basis of experiments that reveal the basic properties of an electric field. Be convinced of the reality of the existence of an electric field on the basis of experiments that reveal the basic properties of an electric field.
What two types of charges exist in nature, how are they called and designated? How do bodies with the same charges interact with each other? How do bodies with opposite charges interact with each other? Can one and the same body, for example, an ebonite stick, become electrified under friction, sometimes negatively, sometimes positively? Is it possible to charge only one of the contacting bodies during electrification by friction? Justify the answer.
We know that rubbing against wool charges sticks made of rubber, sulfur, ebonite, plastic, and cardboard. Does this charge the wool? a) Yes, because friction electrification always involves two bodies, in which both are electrified. b) No, only sticks are charged.
Homework Read and answer questions n Creative Activity: Make a homemade electroscope.
Why is the rod of an electroscope always made of metal? Why does the electrometer discharge when you touch the ball (rod) with your fingers? Will closely spaced electric charges interact in airless space (for example, on the Moon, where there is no atmosphere)? Why does the lower end of the lightning rod need to be buried in the ground, to ground the working electrical appliances?
In the electric field of a uniformly charged ball at point A there is a charged speck of dust. How is the force acting on a speck of dust from the field directed? Does the field of a speck of dust act on the ball? In the electric field of a uniformly charged ball at point A there is a charged speck of dust. How is the force acting on a speck of dust from the field directed? Does the field of a speck of dust act on the ball? What is the difference between the space surrounding an electrified body from the space surrounding a non-electrified body? How is the charge of the electroscope judged by the angle of divergence of the leaves of the electroscope? How is the charge of the electroscope judged by the angle of divergence of the leaves of the electroscope?
§ 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.
Electroscope (from the Greek words "electron" and skopeo - observe, detect) - a device used to detect electrical charges.
Purpose of the device:
Charge detection;
Determination of the sign of the charge;
Estimating the amount of charge.
The 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 body, closed with glass lids.
The principle of operation of the electroscope is based on the phenomenon of electrification. When a rubbed glass rod (positively charged) touches the device (electroscope), electric charges will flow through the rod to the leaves. Having the same sign of the charge, the bodies will begin to repel, so the leaves of the electroscope will disperse at a certain angle. The consumption of leaflets at an angle of greater value occurs when a larger charge is imparted to the electroscope, which means that it leads to an increase in the repulsive force between the bodies (Fig.). Consequently, by the angle of divergence of the leaves, one can find out about the magnitude of the charge of the electroscope. If you bring a body with a negative charge 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 arrow, with the help of which, by the angle of deflection, one can find out about the amount of charge that was imparted to the rod of the electrometer.
§ 2 Electric field and its characteristics
Bodies are electrified as follows: they transfer a positive or negative charge by 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 the body "understand" that the charge of another must be attracted or repulsed? To answer this question, you need to find out a special form of matter - "electric field".
We electrify a metal ball of the same name (of the same sign) on a plastic stand and a light cork ball on a thread (let's call it a test ball). We will transfer it to various points in space around the large ball. We will notice that at every point in space around the electrified body there is a force acting on the test ball. The fact that it exists is observed by the deflection of the ball thread. As the ball moves away from the test ball, the ball on the thread deviates weaker, therefore, the force acting on it becomes less and less (in terms of 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 act on other bodies.
An electric field is a special type 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, as it acts on material objects (a light free body - a 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 the human senses.
4. Does not have a certain size, border, shape.
5. Occupies all the space surrounding the given charged body.
6. As the distance from the charge increases, the field weakens.
7. Has energy.
8. Two principles are inherent in electric fields: the principle of independence (if there are several fields, then each field exists independently of the other), the principle of superposition (overlapping) - the fields do not distort each other.
9. There is about a charged body, particles. Any charged body has its own electric field.
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 of force
To graphically represent the field and find out its direction of propagation, it is necessary to use the method of field lines.
For this, we will conduct an experiment.
Take two metal balls on plastic supports, as well as a needle, also mounted on a support. Place the balls at a distance of 40-50 cm from each other, and between them - a stand with a needle. Let's balance dry wood chips on it. As you can see, the balls have different signs of charges; we will see that the chip will unfold so as to be on the straight line connecting the balls (see the upper part of the figure).
If you place the sliver in different positions near the balls (see fig.), We note that it will take position on the mentally drawn arched lines connecting the balls; this is what the electric field lines look like.
Let's demonstrate an interesting case: there are charged bodies. Place a glass over them, and put 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). On the 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 with more "frequent" lines where a larger electric charge is found, and hence a large electric force when this field is applied to the body. The field line model shows the magnitude of the force and the direction of the action of the field on the 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 "associated" with the charge. When the charge moves to the other side, the field instantly follows it.
List of used literature:
- Physics. Grade 8: Textbook for educational institutions / A.V. Peryshkin. - M .: Bustard, 2010.
- Physics 7-9. Textbook. I.V. Krivchenko.
- Physics. Directory. O.F. Kabardin. - M.: AST-PRESS, 2010.
Slide 2
Electroscope
Slide 3
matter matter field solid state liquid state gaseous state plasma electric magnetic gravitational nuclear
Slide 4
Comparison of field and substance properties
substance 1. Impenetrable 2. Has volume and shape 3. The field is felt visually and tactilely 1. Mutually permeable 2. Not limited in space 3. Not perceived by the senses
Slide 5
Electric field properties
1. Exists around charged bodies 2. Invisible, determined by action and with the help of devices 3. Depicted using lines of force 4. Lines indicate the direction of action of the force acting from the field on a positively charged particle placed in it.
Slide 6
What kind of charge do the balls have?
Slide 7
Count up ...
How many excess electrons are there in a body with a charge of 4.8 10-16 C? Identical metal balls with charges -7q and 11q 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 the modulus of charge on it?
Slide 8
Test yourself:
1. Identical metal balls with a charge of 7e 15e were brought into contact, then moved apart to the same distance. What is the charge of the balls? 2. Can we say that the charge of a system is the sum of the charges of 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?
Slide 9
5. If the body is electrically neutral, does this mean that it does not contain electric charges? 6. If in a closed system the number of charges has decreased, does this mean that the charge of the entire system has decreased? 7.How do opposite charges interact? 8. How many kinds of charges does a gold atom contain? 9. What is the structure of Thomson's atom?
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