EntranceElectric field: division of electric charge and electroscope. Presentation on the topic “electroscope electric field” Why do we need an electroscope and an electrometer
Lesson objectives: To become familiar with the structure of an electroscope. Get acquainted with the device of an 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. Convince yourself of the reality of existence electric field based on experiments revealing the basic properties of the electric field. Convince yourself of the reality of the existence of an electric field based on experiments that reveal the basic properties of the electric field.
What two types of charges exist in nature, what are they called and designated? How do bodies with like charges interact with each other? How do bodies with opposite charges interact with each other? Can the same body, for example an ebonite stick, become electrified either negatively or positively when friction occurs? Is it possible to charge only one of the contacting bodies during electrification by friction? Justify your answer.
We know that sticks made of rubber, sulfur, ebonite, plastic, and cardboard are charged by rubbing them with wool. Does this charge the wool? a) Yes, because electrification by friction always involves two bodies, in which both are electrified. b) No, only sticks are charged.
Homework Read and answer questions Creative task: make a homemade electroscope.
Why is the electroscope rod always made of metal? Why does the electrometer discharge if you touch its ball (rod) with your fingers? Will nearby electric charges interact in airless space (for example, on the Moon, where there is no atmosphere)? Why should the lower end of the lightning rod be buried in the ground and why should operating electrical appliances be grounded?
There is a charged speck of dust in the electric field of a uniformly charged ball at point A. What is the direction of the force acting on the dust grain from the field? Does the field of a speck of dust affect the ball? There is a charged speck of dust in the electric field of a uniformly charged ball at point A. What is the direction of the force acting on the dust grain from the field? Does the field of a speck of dust affect the ball? How does the space surrounding an electrified body differ from the space surrounding a non-electrified body? How do you judge its charge by the angle of divergence of the leaves of an electroscope? How do you judge its charge by the angle of divergence of the leaves of an electroscope?
Goals:
students' knowledge about the electrification of bodies,
to form students' ideas about
electric field and its properties, introduce
with an electroscope (electrometer) device.
developing the ability to make more general conclusions and
generalizations from observations.
ideological ideas, knowability of phenomena and
properties of the surrounding world, increasing
cognitive interest of students with
using ICT.
After the lesson the student knows:
- Structure and purpose of an electroscope
(electrometer). - Concepts of electric field, electric forces.
- Conductors and dielectrics.
- Identify and systematize what they have
knowledge about the electrification of bodies. - Explain the action of the electric field on
electric charge introduced into it. - Deepens knowledge about the electrification of bodies.
- Develops intellectual skills.
Lesson structure:
- Organizational stage.
- Repetition to update previous knowledge.
- Formation of new knowledge.
- Consolidation, including application of new knowledge in
changed situation. - Homework.
- Summing up the lesson.
- Electroscope (1 copy).
- Electrometer (2 copies), metal
conductor, ball. - Electrophoric machine.
- "Sultans".
- Glass and ebonite stick; (wool, silk).
- Presentation.
| Structural elements of the lesson | Teacher activities | Student activities |
| Organizing time | Ensures overall student readiness to work. | The teachers are listening. |
| Motivational - indicative | In order to repeat the material, learned in the previous lesson, conduct a short frontal poll: 1. What are the two types of charges?
Can the same body, for example ebonite Is it possible to charge during electrification by friction? Is the expression correct: “Friction creates 2. Offers to complete a written test | 1. Answer questions. 2. |
| Formation of new knowledge | Electrification of bodies can be carried out not only by friction, but also by contact. Demonstration of experience (to illustrate theoretical conclusions): a) bring the nael. b) the sleeve is attracted and then repelled, c) checking for the presence of a negative charge on | Listen to the teacher, watch the progress experience, which serves as an initial fact for experimental substantiation of electrification upon contact, they participate in a conversation. Do notes in a notebook. |
| On the considered physical phenomenon based on the action of such devices as electroscope and electrometer. Demonstration devices a) electroscope a device for detecting email Charges; Their design is simple: through plastic stopper in a metal frame a metal rod passes through the end which has two sheets of thin paper attached. The frame is covered with glass on both sides. Demonstrating the device and principle of operation electroscope, the teacher asks students questions: How Like the angle of divergence of the leaves of an electroscope For experiments with electricity they use | Listen to the teacher, watch the progress experiment, answer questions, find similarities and differences in design and principle operation of instruments, draw conclusions. |
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| There are substances that are conductors and non-conductors of electrical charge. Experience Demonstration: Charged the electroscope is connected to an uncharged first metal conductor and then glass or an ebonite rod, in the first case the charge goes over, but in the second doesn't go over to uncharged electroscope. | Listening to the teacher, working with the textbook (p. 27 – p. 63), get acquainted with the conductors and dielectrics of electricity, draw conclusions from experience (identification of the second level of knowledge acquisition) |
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| All bodies that are attracted to charged bodies - are electrified, which means they interaction forces act, these forces are called electrical (forces with which the electric field acts on the email entered into it. Charge. All sorts of things a charged body is surrounded by an electric field (special kind matter different from substance). The field of one charge acts on the field of another. | Listen to the teacher, write in notebooks, answer questions during the conversation. |
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| Repetition and systematization knowledge | Conversation on questions to paragraphs 27, 28: | Answer questions (identifying third level of knowledge acquisition) decide quality tasks, applying knowledge in new situations. |
| How to use pieces of paper detect whether the body is electrified? |
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| Describe the structure of the school electroscope. |
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| Like the angle of divergence of the leaves electroscope to judge its charge? |
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| How is space different? surrounding electrified body, from space surrounding non-electrified body? |
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| Solving quality problems (application of knowledge in a new situation). |
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| Why is the electroscope rod always make it metal? |
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| Why does the electrometer discharge if touch its ball (rod) with your fingers? |
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| In an electric field uniformly charged ball in point A there is a charged speck of dust What is the direction of the force acting on a speck of dust from the side of the field? |
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| Does the field of a speck of dust affect the ball? | ||
| Why is the lower end of the lightning rod need to be buried in the ground, working should electrical appliances be grounded? |
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| Will they interact closely? located electric charges in airless space (for example on the Moon, where no atmosphere)? |
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| Organizing homework. | Read and answer questions in paragraphs 27-28. Invites students to make homemade electroscope. | Write down homework in diaries exercise. |
| reflective | The teacher asks the students to answer to questions: which question was the most interesting, the simplest, the most difficult. | Answer questions. |
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.
Slide 2
Electroscope
Slide 3
matter substance field solid state liquid state gaseous state plasma electric magnetic gravitational nuclear
Slide 4
Comparison of properties of field and matter
substance 1. Impenetrable 2. Has volume and shape 3. The field is felt visually and tactilely 1. Interpenetrable 2. Not limited in space 3. Not perceived by the senses
Slide 5
Electric field properties
1. Exists around charged bodies 2. Invisibly, determined by action and with the help of instruments 3. Depicted using lines of force 4. Lines indicate the direction of the force acting from the field on a positively charged particle placed in it.
Slide 6
What charge do the balls have?
Slide 7
Do the math...
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 a body lacks five electrons, then what is the sign and magnitude of the charge on it?
Slide 8
Check yourself:
1. Identical metal balls with charges 7e and 15e were brought into contact, then moved apart to the same distance. What was the charge of the balls? 2. Can we say that the charge of a system consists of the charges of the bodies included in this system? 3.What is the name of the process that leads to the appearance of charges on the body? 4. What is the structure of the Rutherford atom?
Slide 9
5.If a body is electrically neutral, does this mean that it does not contain electrical 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 unlike charges interact? 8. How many types of charges does a gold atom contain? 9.What is the structure of the Thomson atom?
View all slides
§ 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.
An electroscope (from the Greek words “electron” and skopeo - to observe, to detect) is 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 in space around the 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 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 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 charges, we will see that the sliver will unfold so as to be on the straight line connecting the balls (see the upper part of the figure).
If you place a sliver in different positions near the balls (see figure), we note 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:
- Physics. 8th grade: Textbook for general education institutions/A.V. Peryshkin. – M.: Bustard, 2010.
- Physics 7-9. Textbook. I.V. Krivchenko.
- Physics. Directory. O.F. Kabardin. - M.:AST-PRESS, 2010.