D. G. Evstafiev,
Municipal educational institution Pritokskaya secondary school, Romanovsky village, Aleksandrovsky district, Orenburg region.

Comparison of electric and magnetic fields. Grade 11

Lesson plan for repetition and generalization, 11th grade

Guidelines . The lesson is conducted after studying the topic “Magnetic field”. The main methodological technique is highlighting the common and distinctive features of electric and magnetic fields and filling out the table. Sufficiently developed dialectical thinking is assumed, otherwise it will be necessary to make digressions of a philosophical nature. Comparing the electric and magnetic fields leads students to the conclusion about their relationship, on which the next topic is based - “Electromagnetic induction”.

Physics and philosophy consider matter as the basis of all things, which exists in different forms. It can be concentrated within a limited area of ​​space (localized), but it can, on the contrary, be delocalized. The first state can be associated with the concept substance, the second – the concept field. Along with specific physical characteristics, these conditions also have common ones. For example, there is the energy of a unit volume of matter and there is the energy of a unit volume of field. The properties of matter are inexhaustible, the process of cognition is endless. Therefore, all physical concepts must be considered in development. For example, modern physics, unlike classical physics, does not draw a strict boundary between field and matter. In modern physics, field and matter mutually transform: matter turns into field, and field turns into matter. But let’s not get ahead of ourselves, but let’s remember the classification of forms of matter. Let's look at the diagram on the board.

Try using the diagram to compose a short story about the forms of existence of matter. ( After the students answer, the teacher reminds them that The consequence of this is the similarity of the characteristics of gravitational tion and electric fields, which was revealed lebut in previous lessons on the topic “Electric field” .) The conclusion suggests itself: if there is a similarity between the gravitational and electric fields, then there must be a similarity between the electric and magnetic fields. Let's let's compare the properties and characteristics of the fields in the form of a table similar to the one we did with comparison of gravitational and electric fields.

Electric field	A magnetic field
Field sources
Electrically charged bodies	Moving electrically charged bodies (electric currents)
Field indicators
Small pieces of paper. Electric sleeve. Electric "sultan"	Metal filings. Closed circuit with current. Magnetic needle
Experienced Facts
Coulomb's experiments on the interaction of electrically charged bodies	Ampere's experiments on the interaction of conductors with current
Graphic characteristics
Electric field strength lines in the case of stationary charges have a beginning and an end (potential field); can be visualized (quinine crystals in oil)	The magnetic field lines are always closed (vortex field); can be visualized (metal filings)
Power characteristic
Electric field strength vector E. Size: Direction:	Magnetic field induction vector B. Size: . Direction is determined by the left hand rule
Energy characteristics
The work done by the electric field of stationary charges (Coulomb force) is zero when going around a closed trajectory	The work done by the magnetic field (Lorentz force) is always zero
Action of a field on a charged particle
The force is always non-zero: F = qE	The force depends on the speed of the particle: it does not act if the particle is at rest, and also if
Matter and field
.

Conclusion

1. When discussing field sources, it is good to compare two natural stones to increase interest in the subject: amber and magnet.

Amber - a warm stone of amazing beauty - has an unusual property that is conducive to philosophical constructions: it can attract! Being rubbed, it attracts dust particles, threads, pieces of paper (papyrus). It was for this property that they were given names in ancient times. That's what the Greeks called itelectron – attractive; Romans – harpax – robber, and the Persians - cowboy, i.e. capable of attracting chaff . It was considered magical, medicinal, cosmetic...

Another stone known for thousands of years, a magnet, was considered just as mysterious and useful. In different countries the magnet was called differently, but most of these names are translated as loving. This is how the ancients poetically noted the property of pieces of a magnet to attract iron.

From my point of view, these two special stones can be considered as the first natural sources of electric and magnetic fields to be studied.

2. When discussing field indicators, it is useful to simultaneously demonstrate with the help of students the interaction of an electrified ebonite rod with an electric sleeve and a permanent magnet with a closed loop carrying current.

3. Visualization of power lines is best demonstrated using screen projection.

4. Division of dielectrics into electrets and ferroelectrics - additional material. Electrets are dielectrics that maintain polarization for a long time in the absence of an external electric field and create their own electric field. In this sense, electrets are similar to permanent magnets that create a magnetic field. But this is another similarity with hard ferromagnets!

Ferroelectrics are crystals that have (in a certain temperature range) spontaneous polarization. As the external field strength decreases, the induced polarization is partially retained. They are characterized by the presence of a limiting temperature - the Curie point, at which the ferroelectric becomes an ordinary dielectric. Again similarities with ferromagnets!

After working with the table, the discovered similarities and differences are collectively discussed. Similarity underlies a single picture of the world; differences are explained so far at the level of different organization of matter, or better to say, the degree of organization of matter. The mere fact that a magnetic field is detected only near moving electric charges (as opposed to an electric one) makes it possible to predict more complex methods for describing the field, a more complex mathematical apparatus used to characterize the field.

Dmitry Georgievich Evstafiev – hereditary physics teacher (father, Georgy Sevostyanovich, a participant in the Great Patriotic War, worked for many years at the Dobrinsky secondary school, combining teaching with the duties of a school director), graduated in 1978 Physics and Mathematics of the Orenburg State Pedagogical Institute named after. V.P. Chkalova, majoring in Physics, teaching experience 41 years. Since 1965 he has been working at the municipal educational institution Pritokskaya Secondary School, and was its director for several years. He was awarded three times with certificates of honor from the Orenburg Regional District. Pedagogical credo: “Do not be satisfied with what has been achieved!” Many of its graduates graduated from technical universities. Together with his wife, they raised five children, three work in schools in the Orenburg region, two study at the history and philological faculties of the Orenburg State Pedagogical University. Son Sergei is the winner of the All-Russian competition “The Best Teachers of Russia” in 2006, a computer science teacher, works in the regional center - the village of Novosergievka. Hobby: beekeeping.

““The phenomenon of electromagnetic induction” physics” - An EMF variable is connected to the primary winding. Current strength. The expressions for circulation are always valid. The induced current is caused by a change in the flux of the magnetic induction vector. The work of moving a unit charge along a closed circuit. Its mechanical energy increases. The phenomenon of self-induction was discovered by the American scientist J. Henry.

“Field induction” - Work to move a unit charge. Braking action. Conductor. Charges. High frequency currents. Classical electrodynamics. Part of an expression. Induction currents. The conductor is motionless. Circuit. The current is almost evenly distributed throughout the volume of the wires. Faraday Michael. A magnetic field. Conductors in HF.

“Study of the phenomenon of electromagnetic induction” - The mechanism of occurrence. Faraday's law is universal. Alternating magnetic field. Law of electromagnetic induction. Differences between a vortex electric field and an electrostatic one. Currents (Foucault currents) are closed in volume. Movement of the copper comb. Lorentz force. Magnetic induction flux. DFW. Toki Fuko. Stokes formula.

“Electromagnetic induction” - Sinkwine. Michael Faraday. Phenomenon. Video fragment. Northern tip of the arrow. Faraday's experiments. Test sheet with tasks. Historical reference. Electromagnetic induction and device. Chinese wisdom. Induction current. Warm up. The phenomenon of electromagnetic induction. Point. Conductor. Unipolar induction. Magnetic needle.

“Self-induction and inductance” - Units of measurement. Inductance. Coil inductance. Magnetic flux through the circuit. Magnetic field energy. The phenomenon of EMF occurrence. Conclusion in electrical engineering. Self-induction. Manifestation of the phenomenon of self-induction. Current magnetic field energy. Magnetic flux. Magnitude. Conductor. Self-induced emf.

“Electromagnetic induction of Faraday” - Questions. Magnet movement time. solving problems of linear structure. Discovered by Faraday. The principle of operation of the generator. Appearance of the generator. EMR phenomenon. Physical education minute. Induction current. The phenomenon of electromagnetic induction. Experience. Systematize knowledge.

There are 18 presentations in total

Lesson 15. Vortex electric field. EMF induction in moving conductors

Purpose: to find out the conditions for the occurrence of EMF in moving conductors.

During the classes

I. Organizational moment

II. Repetition

What is the phenomenon of electromagnetic induction?

What conditions are necessary for the existence of the phenomenon of electromagnetic induction?

How is the direction of the induced current determined by Lenz's rule?

What formula is used to determine the induced emf and what is the physical meaning of the minus sign in this formula?

III. Learning new material

Let's take a transformer. By connecting one of the windings to the AC network, we obtain current in the other coil. Free charges are affected by an electric field.

Electrons in a stationary conductor are driven by an electric field, and the electric field is directly generated by an alternating magnetic field. Changing over time, the magnetic field generates an electric field. The field moves the electrons in the conductor and thereby reveals itself. The electric field that arises when the magnetic field changes has a different structure than the electrostatic one. It is not associated with charges, it does not begin anywhere and does not end anywhere. Represents closed lines. It is called the vortex electric field. But unlike a stationary electric field, the work of a vortex field along a closed path is not zero.

Induction current in massive conductors is called Foucault currents.

Application: melting metals in vacuum.

Harmful effect: unnecessary loss of energy in transformer cores and generators.

EMF when a conductor moves in a magnetic field

When moving the jumperUThe Lorentz force acts on the electrons and does work. Electrons move from C to L. The jumper is the source of the emf, therefore,

The formula is used in any conductor moving in a magnetic field ifIf between vectorsis the angle α, then the formula is used:

BecauseThat

Cause of EDC- Lorentz force. The sign e can be determined by the right hand rule.

IV. Reinforcing the material learned

Which field is called an induction or vortex electric field?

What is the source of the inductive electric field?

What are Foucault currents? Give examples of their use. In what cases do you have to deal with them?

What distinctive properties does an inductive electric field have compared to a magnetic field? Stationary or electrostatic field?

V. Summing up the lesson

Homework

paragraph 12; 13.

An alternating magnetic field generates induced electric field. If the magnetic field is constant, then there will be no induced electric field. Hence, the induced electric field is not associated with charges, as is the case in the case of an electrostatic field; its lines of force do not begin or end on charges, but are closed on themselves, similar to magnetic field lines. It means that induced electric field, like magnetic, is a vortex.

If a stationary conductor is placed in an alternating magnetic field, then an e is induced in it. d.s. The electrons are driven in directional motion by an electric field induced by an alternating magnetic field; an induced electric current occurs. In this case, the conductor is only an indicator of the induced electric field. The field sets in motion free electrons in the conductor and thereby reveals itself. Now we can say that even without a conductor this field exists, possessing a reserve of energy.

The essence of the phenomenon of electromagnetic induction lies not so much in the appearance of an induced current, but in the appearance of a vortex electric field.

This fundamental position of electrodynamics was established by Maxwell as a generalization of Faraday's law of electromagnetic induction.

Unlike the electrostatic field, the induced electric field is non-potential, since the work done in the induced electric field when moving a unit positive charge along a closed circuit is equal to e. d.s. induction, not zero.

The direction of the vortex electric field intensity vector is established in accordance with Faraday's law of electromagnetic induction and Lenz's rule. Direction of force lines of vortex electric. field coincides with the direction of the induction current.

Since the vortex electric field exists in the absence of a conductor, it can be used to accelerate charged particles to speeds comparable to the speed of light. It is on the use of this principle that the operation of electron accelerators - betatrons - is based.

An inductive electric field has completely different properties compared to an electrostatic field.

The difference between a vortex electric field and an electrostatic one

1) It is not associated with electric charges;
2) The lines of force of this field are always closed;
3) The work done by the vortex field forces to move charges along a closed trajectory is not zero.

electrostatic field	induction electric field (vortex electric field)
1. created by stationary electric. charges	1. caused by changes in the magnetic field
2. field lines are open - potential field	2. lines of force are closed - vortex field
3. The sources of the field are electric. charges	3. field sources cannot be specified
4. work done by field forces to move a test charge along a closed path = 0.	4. work done by field forces to move a test charge along a closed path = induced emf