Physics lesson plan (8th grade) on the topic: Divisibility of electric charge. Electron. Atomic structure

21.09.2019

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Electric charge can be transferred from one body to another. To do this, you need to touch another body with an electrified body, and then part electric charge will pass on to him. Figure 8, a shows a device with which you can find out whether the body is electrified. It is called electroscope. In an electroscope, a metal rod is passed through a plastic plug inserted into a metal frame, at the end of which two light leaves are suspended. The frame is covered with glass on both sides.

Let us pass an electrified rod along the rod of the electroscope. The leaves will receive charges of the same sign (the one on the stick) and disperse (Fig. 8, b). The angle of divergence of the leaves depends on the charge that was imparted to them. The greater this charge, the stronger they will repel each other and therefore the greater the angle they will diverge. Conversely, a decrease in the angle of divergence of the leaflets indicates a decrease in the electrical charge.

Figure 9 shows another instrument called an electrometer. Instead of leaves, there is an arrow inside it. When rod A (or a metal ball placed on this rod) is charged, part of it (of the same sign) is transferred to arrow B. Pushing off from the rod, the arrow rotates through a certain angle. By changing this angle one can judge whether the electric charge is increasing or decreasing.

If you touch a charged object (for example, an electrometer ball) with your hand, the object will discharge. Through the hand, the electric charge will go into our body and be distributed over its surface. The same thing will happen if we touch the electrometer ball not with our hand, but with a metal ruler.

Bodies through which electric charges can pass are called conductors electricity. The human body, metals, as well as solutions of salts and acids in water and soil are good guides. Conversely, substances such as amber, glass, rubber, porcelain, ebonite, plastic, silk, nylon, kerosene, air, do not conduct electricity under normal conditions and are therefore called non-conductors or dielectrics. Insulators are made from dielectrics. (Strictly speaking, dielectrics also conduct electricity. However, the electric charge passing through the dielectric for given time, much less than that charge, which under the same conditions passes through conductors, and therefore charge leakage is often imperceptible.)

Let's turn to experience. Let's take two identical electrometers and charge one of them (Fig. 10, a). If you connect these electrometers with a glass rod, no changes will occur. This confirms that glass is a dielectric. If we use a metal rod A (Fig. 10, b) to connect the electrometers, holding it by the non-conducting electricity handle B, then we will see that the initial charge will be divided into two equal parts: half of the charge will transfer from the first ball to the second. (If the second ball were larger than the first, then more than half of the charge would transfer to it: the larger the body to which the charge is transferred, the larger part of the charge transfers to it. This is based on grounding- transfer of charge to the Earth. Earth large compared to the bodies on it. Therefore, when a charged body comes into contact with the Earth, it gives up almost all of its charge and becomes practically neutral.)
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Let's continue the experiment. Let's disconnect the electrometers and touch the second ball with our hand. This will cause it to lose charge and discharge. Let's connect it again with the first ball, on which half of the original charge remains. The remaining charge will again be divided into two equal parts, and a fourth of the original charge will remain on the first ball. In the same way one can obtain one-eighth, one-sixteenth of the original charge, etc.

Questions arise: how long can the charge be reduced? Is there a limit to the division of electric charge? To find out this, it was necessary to perform more complex and accurate experiments than those described above, since very soon the charge remaining on the ball turns out to be so small that it cannot be detected using a school electrometer.

More precise experiments have shown that the electric charge cannot be reduced indefinitely: it has a divisibility limit. Absolute value(module) of the smallest charge is denoted by the letter e and is called elementary charge:

e = 0.00000000000000000016 Cl = 1.6 · 10 -19 Cl.

This charge is billions of times less than what is usually obtained in experiments on the electrification of bodies by friction.

1. What are electroscopes and electrometers used for? 2. How, with a charged electrometer and objects from various substances, is it possible to establish which of them are conductors and which are not? 3. Give examples of conductors. 4. What substances are called dielectrics? Give examples. 5. Describe an experiment that allows charge division to occur. 6. Is it possible to reduce the charge indefinitely? 7. What is grounding? What property is it based on? 8. What charge is called elementary?

Lesson objectives:

show that electric charge can be divided into parts;
introduce students to electrons;
introduce students to Rutherford’s planetary model of the atom;
develop students’ abilities to analyze, compare, and draw conclusions.
develop students' thinking.

Visual aids and equipment:

presentation;
multimedia projector;
electroscopes, metal wire with an insulated handle, glass and ebonite rods, pieces of fur, silk;
"sultans" on a stand, electrophore machine;
table " Periodic table chemical elements of Mendeleev".

During the classes

Updating knowledge

Let's electrify the "sultan" using an electrophore machine. Why did the stripes of the “sultan” go in different directions?

Using an electrophore machine, we will inform the two “sultans” first of opposite charges, and then of like charges. Explain the observed phenomena. Why do the stripes of “sultans” attract in the first case, and repel in the second?

What is the name of the device?

Let us touch the electroscope ball with an electrified glass rod. Why does the electroscope needle deviate?

What is the means of electrical interaction between charged bodies?

Let's solve the crossword puzzle and find out what we will talk about in class today. (Slide 1)

A method of imparting an electrical charge to the body.

A substance that does not conduct electricity.

A substance that conducts electricity well.

A device used to detect and measure electrical charge.

Divisibility of electric charge.

Let's charge the electroscope and connect it with an uncharged electroscope using a metal wire.

What happened? Why?

(Half of the charge of the first ball transferred to the second, the charge was divided into two equal parts) Let's repeat the experiment. The charge of the first ball has also decreased by half. The first electroscope will retain some of its original charge. This means that the electric charge can divide.

Do you think it is possible to divide a charge infinitely?

Why? Is there a limit to charge division?

The Russian scientist A.F. Ioffe and the American scientist R. Millikan proved that this division has a limit. It was concluded that there is a particle in nature that has the smallest negative charge. (Slide 3) This particle was called an electron. (Slide 4)

Electron - elementary particle, having a negative charge.

The particle with the least positive charge is called a proton.

Electrons and protons are part of an atom.

The charge of a proton is equal in magnitude to the charge of an electron.

Scientist Rutherford experimentally substantiated the planetary model of the atom (Slide 5):

in the center of the atom there is a positively charged nucleus;
Negatively charged electrons move around the nucleus.

Why do you think the atomic model is called planetary?

The nucleus consists of protons and neutrons.

What charge do protons have? Neutrons? Do you think an atom has an electric charge?

The number of electrons is equal to the number of protons, which means the charge of the nucleus is equal in magnitude to the charge of the electrons, therefore, the atom is neutral.

The masses of a proton and neutron are many times greater than the mass of an electron, so the mass of an atom is concentrated in the nucleus.

Atoms of different elements differ from each other in the number of protons, neutrons and electrons.

Find aluminum in the periodic table. (Slide 6)

What is the serial number of aluminum? What is its atomic mass?

Determine the composition of hydrogen, helium, lithium atoms. (Slides 7,8,9) Which atom model is shown in the picture? (Slide 10) Why is an atom neutral?

An atom that has lost one or more electrons will have a positive charge. It is called a positive ion.

An atom that has gained one or more electrons will have a negative charge. It is called a negative ion. (Slide 11)

Consolidation of the studied material.

Let's check how you have mastered the topic of today's lesson. (Slide 12,13)

At the center of the atom is ______

___________ move around the nucleus

The nucleus of an atom consists of ____________________

The nucleus has a _______________ charge.

Electrons have ______________ charge.

Protons have _______________ charge.

Neutrons have _______________ charge.

An atom has a _______________ charge.

An atom that has lost one or more electrons is called ________________

An atom that has gained one or more electrons is called _____________

Determine the composition of the atom and fill out the table (Slide 14):

Homework: Paragraph 29,30, exercise 11.

>>Physics: Electroscope Divisibility of electric charge

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If you have corrections or suggestions for this lesson,

You already know that to explain thermal phenomena, knowledge about molecular structure substances. Is it possible to explain the phenomenon of electrification using ideas about the molecular structure of matter? It is known that in the normal state molecules and atoms have no electrical charge. Consequently, electrification cannot be explained by their movement. If we assume that in nature there are particles that have an electric charge, then when the charge is divided, the division limit should be discovered.

Rice. 38. Charging the electroscope

Let's do the following experiment. Let's charge the electroscope (Fig. 38), and then use a metal wire to connect it to another, uncharged electroscope (Fig. 39). As soon as the wire touches the balls of both electroscopes, half the charge of the first ball will transfer to the second.

Rice. 39. Divisibility of electric charge

This means that the original charge is divided into two equal parts.

If an uncharged electroscope is again connected to the first electroscope, on which half of the original charge remains, then 1/4 of the original charge will remain on it. In the same way, each of these separated charges can be again divided into two equal parts, etc.

Is there a limit to charge division? Could it be possible to obtain a charge of such a magnitude that it is no longer amenable to further division?

To answer these questions, even more complex experiments had to be carried out. The fact is that the charge remaining on the electroscope ball becomes so small that it cannot be detected using an electroscope. For this purpose, to divide the charge into small portions, it was transferred not to balls, but to small grains of metal or liquid. Then we measured the charge obtained on these small bodies, which turned out to be billions of billions of times less than in the experiments we considered (see Fig. 38). But it was not possible to separate the charge beyond a certain value. This suggested that there is a charged particle that has the smallest charge that cannot be separated.

Milliken Robert (1868-1953)
American experimental physicist. Experimentally proved the existence of particles with the smallest charge. Nobel Prize Laureate

The existence of the smallest particles having the smallest electrical charge has been proven by many experiments. Such experiments were carried out by the Soviet scientist Abram Fedorovich Ioffe and the American scientist Robert Millikup. In their experiments, they electrified small grains of zinc dust. The charge of the dust particles was changed and calculated. This happened several times. In this case, the charge turned out to be different each time. But all its changes were an integer number of times (i.e. 2, 3, 4, etc.) greater than some certain minimum charge. This result can only be explained this way. Only the smallest charge (or an integer number of such charges) is attached to or separated from a grain of zinc dust. This charge no longer divides. The particle with the smallest charge is called electron.

Ioffe Abram Fedorovich (1880-1960)
Russian physicist, academician. Creator of the Russian scientific school. Conducted research on measuring the charge of an electron.

Pendant Charles Augustin (1763-1806)
French physicist, military engineer. Invented a device to establish the basic laws of electrical and magnetic interactions.

The electron is very small. The mass of the electron is 9.1 10 -31 kg. This mass is approximately 3,700 times less than the mass of a hydrogen molecule, which is the smallest of all molecules.

Electric charge is one of the main properties of an electron. It is impossible to imagine that charge can be removed from an electron. They are inseparable from each other.

Electric charge is a physical quantity. It is denoted by the letter q. The unit of electric charge is the coulomb (C). This unit is named after the French physicist Charles Coulomb.

An electron is a particle with the least negative charge. Its charge is -1.6 10 -19 C.

Questions

How can you experimentally show that an electric charge is divided into parts?
Does electric charge have a divisibility limit?
What is the particle with the smallest charge called? What do you know about the charge and mass of an electron?

Lesson topic

The structure of the atom.

Lesson objectives:

Educational: introduce the concept of an electron as a particle with the smallest electrical charge, consider models of the structure of the atom according to Thomson and Rutherford, give an idea of positive and negative ions;

Developmental: develop students’ abilities to analyze, compare, draw conclusions;

Educational: developing the idea of the materiality of the world, cause-and-effect relationships between phenomena, cultivating interest in the subject.