Electromagnetic induction. Magnetic flux. Magnetic flux (Eryutkin E.S.) Lesson summary magnetic field induction magnetic flux
LESSON OUTLINE
Topic “Magnetic flux. The phenomenon of electromagnetic induction ", grade 9
Lesson objectives:
The goal is to achieve educational results.
Personal results:
- development of cognitive interests, intellectual and creative abilities;
- independence in acquiring new knowledge and practical skills;
- the formation of value attitudes towards learning outcomes.
Metasubject results:
- mastering the skills of independent acquisition of new knowledge, organization of educational activities, goal setting, planning;
- mastering methods of action in non-standard situations, mastering heuristic methods for solving problems;
- the formation of the ability to observe, highlight the main thing, explain what he saw.
Subject results:
– know: magnetic flux, induction current, electromagnetic induction phenomenon;
– understand: flux concept, electromagnetic induction phenomenon
– be able to: determine the direction of the induction current, solve typical problems of the OGE.
Lesson type: learning new material
Lesson form: research lesson
Technologies: elements of critical thinking technology, problem learning, ICT, problem dialogue technology
Lesson equipment: a computer, an interactive whiteboard, a coil, a tripod with a foot, a strip magnet - 2 pcs., a demonstration galvanometer, wires, a device for demonstrating Lenz's rule.
During the classes
Start: 10.30
1. Organizational stage (5 minutes).
Hello guys! Today I will give a physics lesson, my name is Innokenty Innokentyevich Malgarov, a physics teacher at the Kyllakh school. I am very glad to work with you, with high school students, I hope today's lesson will be productive. In today's lesson, attentiveness, independence, resourcefulness are assessed. The motto of our lesson with you is "Everything is very simple, you just need to understand!" Now, the deskmates look at each other, wish you luck and shake hands. For feedback, I will sometimes clap my hands and you will repeat. Check it out? Wonderful!
Please look at the screen. What do we see? That's right, a waterfall and a strong wind. What word (one!) Unites these two natural phenomena? Yes, flow... Water flow and air flow. Today we will also talk about flow. Only about a stream of a completely different nature. Can you guess what? What are the related topics that you covered earlier? That's right, with magnetism. Therefore, write the lesson topic on your worksheets: Magnetic flux. The phenomenon of electromagnetic induction.
Start: 10.35
2. Updating knowledge (5 minutes).
Exercise 1. Please look at the screen. What can you say about this picture? Gaps in the worksheets should be filled in. Check with your partner.
1. Around the conductor with current there is a magnetic field... It is always closed;
2. The strength characteristic of the magnetic field is vector of magnetic induction 0 "style =" border-collapse: collapse; border: none ">
Look at the screen. By analogy, fill in the second column for the contour in the magnetic field.
Please take a look at the demo table. On the table, you see a swing arm stand with two aluminum rings. One whole and the other with a slot. We know that aluminum is not magnetic. We begin to insert the magnet into the slotted ring. Nothing happens. Now let's start to insert the magnet into the whole ring. Pay attention, the hundredth ring starts to "run away" from the magnet. We stop the movement of the magnet. The ring also stops. Then we begin to carefully remove the magnet. Now the ring begins to follow the magnet.
Try to explain what you saw (students try to explain).
Please look at the screen. A hint is hidden here. (Students come to the conclusion that changing the magnetic flux can produce an electric current.)
Task 4. It turns out that if you change the magnetic flux, you can get an electric current in the circuit. You already know how to change the flow. How? That's right, you can strengthen or weaken the magnetic field, change the area of the contour itself and change the direction of the contour plane. Now I will tell you one story. Listen carefully and complete task 4 in parallel.
In 1821, the English physicist Michael Faraday, inspired by the work of Oersted (the scientist who discovered the magnetic field around a conductor with current), set himself the task of obtaining electricity from magnetism. For almost ten whole years, he carried wires and magnets in his pants pocket, trying unsuccessfully to get an electric current out of them. And one day, quite by accident, on August 28, 1831, he did it. (Prepare and show a demo). Faraday found that if the coil is quickly put on (or removed from) a magnet, then a short-term current arises in it, which can be detected using a galvanometer. This phenomenon began to be called electromagnetic induction.
This current is called induction current... We said that any electric current generates a magnetic field. The induction current also creates its own magnetic field. Moreover, this field interacts with the field of a permanent magnet.
Now, using your interactive whiteboard, determine the direction of the induction current. What conclusion can be drawn regarding the direction of the magnetic field of the induction current?
Start: 11.00
5. Application of knowledge in different situations (10 minutes).
I suggest you solve the tasks that are offered in the OGE in physics.
Task 5. A strip magnet is brought to a solid aluminum ring suspended on a silk thread at a constant speed (see figure). What will happen to the ring at this time?
1) the ring will remain alone
2) the ring will be attracted to the magnet
3) the ring will be repelled by the magnet
4) the ring will begin to turn around the thread
Task 6.
1) Only in 2.
2) Only in 1.
4) Only in 3.
Start: 11.10
5. Reflection (5 minutes).
It's time to evaluate the results of our lesson. What new things have you learned? Have you achieved the goals that were set at the beginning of the lesson? What was difficult for you? What did you particularly like? How did you feel?
6. Homework information
Find in your textbooks the topic "Magnetic flux", "The phenomenon of electromagnetic induction" read and check if you can answer the self-test questions.
Thanks again for your cooperation, for your interest and, in general, for a very interesting lesson. I wish you to study physics well and, on its basis, to learn the structure of the world.
"Everything is very simple, you just need to understand!"
Surname, name of the student _______________________________________ student (s) of the 9th grade
Date "____" ________________ 2016
WORK SHEET
Lesson topic: ___________________________________________________________________
__________________________________________________________________________
644 "style =" width: 483.25pt; border-collapse: collapse; border: none ">
Task 4. Fill the gaps.
1. The phenomenon of the emergence of a current in a closed conductor (circuit) when the magnetic field permeates this circuit is called _______________________;
2. The current that occurs in this case in the circuit is called ___________________________;
3. The magnetic field of the circuit created by the induction current will be directed to the __________________ magnetic field of the permanent magnet (Lenz's Rule).
https://pandia.ru/text/80/300/images/image006_55.jpg "align =" left hspace = 12 "width =" 238 "height =" 89 "> Task 6. There are three identical metal rings. A magnet is removed from the first ring, a magnet is inserted into the second ring, a stationary magnet is located in the third ring. In which ring does the induction current flow?
1) Only in 2.
2) Only in 1.
Lesson topic:
Discovery of electromagnetic induction. Magnetic flux.
Target: to familiarize students with the phenomenon of electromagnetic induction.
During the classes
I. Organizational moment
II. Knowledge update.
1. Frontal poll.
- What is Ampere's hypothesis?
- What is magnetic permeability?
- What substances are called para- and diamagnets?
- What are ferrites?
- Where are ferrites used?
- How is it known that there is a magnetic field around the Earth?
- Where are the North and South magnetic poles of the Earth?
- What processes are taking place in the Earth's magnetosphere?
- What is the reason for the existence of a magnetic field around the Earth?
2. Analysis of experiments.
Experiment 1
The magnetic needle on the stand was brought to the bottom and then to the top end of the tripod. Why does the arrow turn towards the lower end of the tripod on either side with the south pole, and towards the upper end with the north end?(All iron objects are in the earth's magnetic field. Under the influence of this field, they are magnetized, with the lower part of the object revealing the north magnetic pole, and the upper part of the south.)
Experiment 2
In the large cork, make a small groove for the piece of wire. Dip the plug into the water, and put the wire on top, placing it parallel. In this case, the wire, together with the plug, turns and is installed along the meridian. Why?(The wire has been magnetized and is set in the earth's field like a magnetic needle.)
III. Learning new material
Magnetic forces act between moving electric charges. Magnetic interactions are described based on the concept of a magnetic field that exists around moving electric charges. Electric and magnetic fields are generated by the same sources - electric charges. It can be assumed that there is a connection between them.
In 1831 M. Faraday confirmed this experimentally. He discovered the phenomenon of electromagnetic induction (slides 1,2).
Experiment 1
We connect the galvanometer to the coil, and we will push the permanent magnet out of it. We observe the deflection of the galvanometer needle, a current (induction) has appeared (slide 3).
A current in a conductor occurs when the conductor is in the area of an alternating magnetic field (slide 4-7).
Faraday represented an alternating magnetic field as a change in the number of lines of force penetrating the surface bounded by a given contour. This number depends on the induction V magnetic field, from the area of the contour S and its orientation in this field.
Ф = BS cos a - magnetic flux.
F [Wb] Weber (slide 8)
The induction current can have different directions, which depend on whether the magnetic flux penetrating the circuit decreases or increases. The rule for determining the direction of the induction current was formulated in 1833. E. X. Lenz.
Experiment 2
Insert a permanent magnet into a lightweight aluminum ring. The ring is repelled from it, and when extended, it is attracted to the magnet.
The result is independent of the polarity of the magnet. Repulsion and attraction is explained by the appearance of an induction current in it.
When the magnet is pushed in, the magnetic flux through the ring increases: the repulsion of the ring shows that the induction current in it has a direction in which the induction vector of its magnetic field is opposite in direction to the induction vector of the external magnetic field.
Lenz's rule:
The induction current always has such a direction that its magnetic field prevents any changes in the magnetic flux, causing the appearance of an induction current(slide 9).
IV. Laboratory work
Laboratory work on the topic "Experimental verification of the Lenz rule"
Devices and materials:milliammeter, coil-coil, arc-shaped magnet.
Progress
- Prepare a table.
Class: 9
Target: through the concepts and formulas of magnetic flux and induction EMF, bring students to an understanding of the rules for determining the direction of induction current.
Equipment:
- SMART interactive whiteboard
- L-micro software, section "Electrodynamics",
- computer matching unit,
- prefix "Oscilloscope",
- inductor and tripod,
- strip magnets,
DURING THE CLASSES
At: Let's remember what a magnetic flux is.
D:
1) formula; Ф = B S Cosα;
2) the number of field lines across the site
At: To make it clear to everyone, draw how you understood what a magnetic flux is.
D: Using the tools of the interactive whiteboard, we draw the lines of the field passing through the contour area (Fig. 1, Fig. 2).
At: Who can increase the magnetic flux? Show how. ( D: increase the number of lines of magnetic induction, increase the area of the ring) (Figure 3, Figure 4)
At: So, in order to reduce the magnetic flux, you need ...
D: Decrease the number of lines, decrease the area of the ring. That is, to "control" the magnetic flux, you can change the magnitude of the magnetic field and the area of the loop.
At: Draw magnetic flux
D: It will not exist at all!
- No, it will be! Field lines are drawn continuously and cover the entire magnet. For convenience, we draw only a part of them.
- During laboratory work, sawdust was collected both at the North Pole and at the South Pole. So there will be magnetic flux here too.
At: Then how did the flip of the magnet affect the magnetic flux?
D: Probably not how. If the magnet and the area are taken as in the previous figure, then nothing will change in size. Ф = ВS
At: How to show that the magnet has turned around?
D: Put a "-" sign
At: Position the ring and magnet so that the flow through the ring is 0.
D: pic 5
At: The formula for the magnetic flux is cosα. From the math handbook
Where is this angle in the picture, between which two directions? The flow can be equal to 0, if the angle is 90 o, this is the perpendicular. And our ring and magnet are parallel (Fig. 6).
D: The field lines have a direction, but the area does not.
At: Remember how this angle is set according to the text in the manual.
D: There is drawn a perpendicular to the frame
This means the angle between the magnetic field vector and the normal. (fig. 7)
At: Check yourself - draw the maximum flow, put all possible options on the board. (Figure 8)
D: The second and third don't fit. There the flow turns out to be negative.
D: So what? The number of lines is the same, so the flow is the same. In experiments with magnets, sawdust did not care which pole to stick to - north or south.
At: Then, in general, why do we need to know the sign of the flow, the angle. The flow is still clear, where is the maximum?
D: ?
At: Demonstration of Faraday's experiment with a coil and magnet.
D: In the experiments of Faraday! We have seen that the direction of the current changes, depending on how we bring in or take out the magnet.
At: Write Faraday's Law in mathematical terms.
D: E = -,
At: Let's try to understand the signs in this law. If we want to get a "positive" direction of the current, then ...
D: The flow should be decreasing. Then ∆Ф< 0 и в
итоге получиться плюс.
D: It can grow, but with a minus sign
At: Draw how the magnet should move.
D: We insert the magnet into the coil, the number of lines increases, which means that the flow increases only with the opposite sign. You can check on numbers (Fig. 9).
D: We remove the magnet from the coil so that the flux is positive, and the change in flux is negative.
At: In the experiment, the direction of the current coincides in both cases. This means that our analysis of the formulas is correct.
At: We will use modern equipment that allows us to see how the direction of the current changes, not only in direction, but also in magnitude over time.
Information is given about the capabilities of the measuring complex "L-micro", a brief explanation of the purpose of devices and devices.
Performing demos
The inductor was fixed with a tripod. The change in the magnetic flux was carried out by moving a strip permanent magnet relative to the inductor. The EMF of induction arising in the inductance coil was fed to the input of the Oscilloscope attachment, which, through a matching unit, transmitted the time-varying electrical signal to the computer and was recorded on the monitor. The oscilloscope was triggered from the signal under investigation in the "waiting" sweep mode at a signal level an order of magnitude lower than the maximum value of the induction EMF. This made it possible to observe the EMF of induction almost completely from the moment the magnetic flux began to change.
Throw through the reel unmarked magnet. A graph of the dependence of the EMF value on time is drawn on the screen. But the graph of current versus time will behave similarly.
Students see that a magnet flying through a coil causes an induction current to appear in it. (fig. 10)
At: Sketch the graph in a notebook.
Homework: write down what happened to the magnetic flux in three stages: the magnet flies up to the coil, moves inside, flies out of it. Sketch your version of the experiment, indicating the poles of the moving magnet.
LESSON IN PHYSICS. PREPARED BY THE TEACHER OF PHYSICS VITALY VASILIEVICH KAZAKOV.
Lesson topic: Magnetic flux
The purpose of the lesson
1. Introduce the definition of magnetic flux;
2. Develop abstract thinking;
3. To educate accuracy, accuracy.
Lesson objectives: Developing
Lesson type Presentation of new material
Equipment: a computer , LCD-projector , projection th screen .
During the classes
1 homework check
1.What is the magnetic induction vector?
1.A axis passing through the center of the permanent magnet;
2. Power characteristic of the magnetic field;
3. Lines of the magnetic field of a straight conductor.
2. Vector of magnetic induction ...
2.Exits from the south pole of the permanent magnet;
3. 1. Select the correct statement (s).
A: magnetic lines are closed
B: magnetic lines are denser in areas where the magnetic field is stronger
B: the direction of the field lines coincides with the direction of the north pole of the magnetic needle placed at the studied point
Only A; 2. Only B; 3.A, B, and C.
4. The figure shows the magnetic field lines. At what point of this field will the maximum force act on the magnetic needle?
1. 3; 2. 1; 3. 2.
5 ... A straight conductor was placed in a uniform magnetic field perpendicular to the lines of magnetic induction, through which a current of 8A flows. Determine the induction of this field if it acts with a force of 0.02 N for every 5 cm of the length of the conductor.
1. 0.05 T 2. 0.0005 T 3.80 T 4. 0.0125 T
Answers: 1-2; 2-3; 3-3; 4-2; 5-1.
2.Exploring new
Statement of a virtual problem.
We came to the next holiday of the plow - Sabantuy. But here, it would seem, chagrin - the rain poured down. I suggest you a competition game in which you have to collect as much water as possible in buckets. (The condition is to collect only rain falling from the sky). Students conduct a heated discussion of who will collect water how: - would run against the rain; - it is desirable to have more dishes; - stand in one place; - run to where the rain is stronger; - keep the bucket perpendicular to the rain. These examples are irrefutable. The children themselves came to the fulfillment of the purpose of the lesson - the determination of the magnetic flux. It remains to draw conclusions and come to mathematical formulations. So, the magnetic flux (rain) depends on:- surface area of the contour (buckets); - vector of magnetic induction (rain intensity); - the angle between the vector of magnetic induction and the normal to the plane of the contour.
Anchoring
And now we fix our conclusions with interactive models.
2.Tutorial: Peryshkin A.V., Gutnik E.M. Physics. Grade 9: Textbook for educational institutions. M .: Bustard, 2009.
3. Physics. 9kl. Lesson plans for textbooks A.V. Peryshkin and Gromova S.V_2010 -364s
4. Tests in physics for the textbookPeryshkin A.V., Gutnik E.M. Physics. Grade 9
Topic: Discovery of the phenomenon of electromagnetic induction. Magnetic flux. Induction current direction. Lenz's rule.
Target: Concept formationelectromagnetic induction, magnetic flux, introduce formulas for magnetic flux, teach how to determine the direction of induction current according to Lenz's rule; developing: the formation of students' skills to compare, independently draw conclusions; educational: the formation of children's awareness of the importance of science.
Equipment: textbook, problem book, magnet, galvanometer, coil.
Lesson type: a lesson in learning new ZUNs.
Must know / be able to: concept - the phenomenon of electromagnetic induction, the history of the discovery, the main formulas of this topic.
During the classes.
Organizing time.
l ... Updating basic knowledge. Repetition of previously studied material.
How is it indicated? Formula? .
Units?[ V]=[ T] .
What force occurs between two interacting conductors with current? .
Formula 
.
How can you determine the direction ? Using the left hand rule: .
What is the force acting on one charged particle in a magnetic field? ... Formula. .
What is equal to if the particle flew in parallel to the lines ?
What happens to a particle when it flies into a magnetic field at an angle ? Begins to move in a spiral because changes the trajectory of its movement.
What is equal to if the particle flew in perpendicular to the lines ? .
What is the trajectory of the particle? Circle.
What is the trajectory of the particle when it flies in parallel to the lines ? Straight.
How to determine the direction ? Using the right hand rule: in the palm of your hand, four fingers - direction , thumb - direction .
II ... Study of new ZUNs.
So far, we have considered electric and magnetic fields that do not change over time. They found out that the electrostatic field is formed by stationary charged particles, and the magnetic field - by moving ones, i.e. electric shock. Now you need to figure out what happens to the electric and magnetic fields that change over time.
After Orsted discovered the connection between electric current and magnetism, Michael Faraday became interested in whether the connection was possible the other way around.
In 1821, Faraday wrote in his diary: "Convert magnetism into electricity."
He conducted many experiments over the years, but all did not give results. He wanted to give up his idea and experiments many times, but something stopped him on August 29, 1831. After numerous experiments that he conducted over 10 years, Faraday achieved his goal: he noticed that an electric current appears in a closed conductor, which is located in a closed magnetic field, his scientist called induction current.
Faraday came up with a series of experiments that are now very simple. He wound on a coil parallel to one another conductors (two wires), which were isolated from each other and connected one end to the battery, and the other to a device for determining the current strength (galvanometer).
He noticed that all the time the galvanometer needle was at rest and did not react when current passed through the electrical circuit. And when he turned on and off the current, the arrow deflected.
It turned out that at the moment when the current passed through the first wire, and when it stopped flowing, the current appeared in the second wire for only a moment.
Continuing his experiments, Faraday found that a simple approximation of a conductor, twisted in a closed curve, to another conductor through which a current flows, is enough for an induction current to form in the first, directed back from the passing current. And if you move the twisted conductor away from the one through which the current flows, then in the first one the induction current of the opposite direction will appear again.
Faraday speculated that electric current could magnetize iron. And can a magnet, in turn, cause an electric current.
For a long time, this relationship could not be detected. The study was carried out in such a way that the coil on which the wire was wound was connected to a galvanometer and a magnet was used, which was lowered into the coil or retracted.
Together with Faraday, Colladon (a Swiss scientist) performed a similar experiment.
During his work, he used a galvanometer, a light magnetic needle of which was placed inside the coil of the device. To prevent the magnet from affecting the arrow, the ends of the coil were brought out to another room.
When Colladon put a magnet in the coil, he went into another room and watched the galvanometer needle, walked back - took the magnet out of the coil and again returned to the room with the galvanometer. And each time he was saddened to be convinced that the galvanometer needle did not deviate, but remained at the zero mark.
If he had to watch the galvanometer all the time and ask someone to take care of the magnet, a wonderful discovery would have been made. But this did not happen. A magnet resting relative to the coil could lie quietly inside it for hundreds of years, without causing a current in the coil.
The scientist was unlucky, these were hard times for science and no one then hired assistants, some because of financial problems, and not who so as not to have to share the discovery
Faraday also faced similar accidents, because he repeatedly tried to get an electric current with the help of a magnet and with the help of a current in another conductor, but to no avail.
But Faraday still managed to make a discovery and, as he wrote in his diaries, he revealed a current in the coil, which he called the induction current.
You can show an experiment with a magnet and a coil. And say: on l.r. you yourself will learn to observe such a phenomenon.
Zn. The phenomenon of generation in space by an alternating magnetic field of an alternating electric. fields calledthe phenomenon of electromagnetic induction.
Induction current in a closed conducting loop (or in a coil) occurs when the number of magnetic induction lines B changes (during the input or output of the magnet, the number of lines changes), which penetrate the surface bounded by the loop.
A physical quantity that is directly proportional to the number of lines of magnetic induction that penetrate a given surface is called the flux of magnetic induction.
[F] = [Wb] Weber
The flux of magnetic induction characterizes the distribution of the magnetic field over a surface bounded by a closed loop.
Magnetic flux Ф (flux of the magnetic induction vector) through a surface with an area Is a value equal to the product of the modulus of the magnetic induction vector To the square and the cosine of the angle between vectors and :
The direction B to the area that it penetrates can be different:
What is the angle between B and ? 0 O A what is equal to?
