My opinion on the research and teaching of electromagnetic induction phenomenon

Introduction The knowledge points of physical electromagnetic induction in senior high school are both important and difficult. Therefore, the author puts forward his own simple views and experiences on this knowledge point, and calls this view the research study of electromagnetic induction phenomenon. If there are any shortcomings, please advise.

Carrying out research-based learning in ordinary senior high schools is an important measure of physics curriculum reform in senior high schools in China, which meets the requirements of quality education with moral education as the core and the cultivation of innovative spirit and practical ability as the focus.

1. Understanding of inquiry learning

Under the guidance of teachers, students learn about experimental research experiments, start from all aspects, use scientific research methods to understand problems and acquire knowledge, so as to deepen their understanding or finally solve problems. This is research-based learning.

1820, Danish physicist Oster discovered the magnetic effect of current and revealed the connection between electricity and magnetism. Inspired by this discovery, people began to consider such a question: since "electricity produces magnetism", is it ok to "generate electricity with magnetic energy"? Many scientists have explored this aspect. Faraday, a British civilian scientist, firmly believes that electricity is closely related to magnetism. After 10 years of unremitting efforts and numerous setbacks and failures, we finally found the condition of generating current by using magnetic field in an accidental opportunity of 183 1 year.

1- 1 Faraday biography

1791September 22nd is a glorious day. Michael faraday, a great scientist, was born in a poor blacksmith family in Newton, Surrey, England. Faraday's life was great, but Faraday's childhood was miserable. In order to solve the problem of food and clothing for the whole family, old Faraday moved to London with Faraday, who was 5 years old, hoping to change the fate of poverty. Unfortunately, God did not bless the Faraday family, but took the life of nine-year-old Faraday. Forced to make a living, michael faraday, who was only nine years old, had to bear a heavy burden of life and go to a stationery store as an apprentice. Four years later, Faraday, 13 years old, went to the bookstore as an apprentice. At first, I was responsible for delivering newspapers, and later I worked as a bookbinder. As the saying goes, "If God wants to be a great man in Sri Lanka, he must first suffer his mind, work his bones and muscles, and starve his body and skin ...". Poverty is unfortunate, and the life of child labor is hard to know. What is commendable is that little Faraday is uneasy about poverty, uneasy about poverty and eager to learn. /kloc-When he was 0/4 years old, he was apprenticed to a man who installed and sold books, and took advantage of this opportunity to read widely. At the age of twenty, he listened to lectures by famous British scientists Humphrey and David, and became interested in it from then on. He wrote to David and finally got him a job as an assistant. Faraday made his great discovery a few years later. Although he has a poor foundation in mathematics, he is unparalleled as an experimental physicist.

18 10, Faraday listened to more than a dozen lectures on natural philosophy given by J. tatum, and began to participate in the learning activities of the municipal philosophy society, from which he received the basic education of natural philosophy. 2 18 12 from February to April, Faraday, 2 1 year-old, was lucky enough to listen to H. David's chemistry lectures four times at the Royal College. The great chemist's profound knowledge immediately attracted the young Faraday. He enthusiastically conveyed every scientific viewpoint of David to his colleagues in the city philosophy association. He carefully arranged the lecture notes, bound them into a beautiful book, named "Sir David's Lecture", and attached a letter eager to do scientific research, which was sent to David on Christmas Eve of 18 12. Faraday's enthusiasm for science touched David, and David was deeply gratified by his carefully arranged and bound "exquisite notebook". At this time, his apprenticeship had expired, so David recommended him to join the Royal College as an assistant in March 18 13. From May 38 to 10 in the same year, I followed David on a scientific investigation trip to the European continent. This trip made Faraday go to a "social university". Along the way, he carefully recorded the contents of David's lectures in various places, learned a lot of scientific knowledge, and met many famous scientists, such as Gay-Lussac and Ampere. I have increased my knowledge and broadened my horizons. By the time 18 15 returned to the Royal Institute in May, Faraday had been able to independently carry out research work under the guidance of David and achieved several chemical research results. Faraday published his first scientific paper in 18 16. From 18I8, we cooperated with J. stoddart to study alloy steel, and pioneered the metallographic analysis method. 1820, he prepared hexachloroethane and tetrachloroethylene by substitution reaction. 182 1 year, director of the royal college laboratory. 1823 saw that he discovered the liquefaction method of chlorine and other gases. He was elected a member of the Royal Society. 1825 In February, he succeeded David as the laboratory director of the Royal Institute. Benzene was discovered in the same year. More importantly, his contribution to electrochemistry (the study of chemical effects produced by electric current). After many detailed experiments, Faraday summed up two laws of electrolysis and named them after him, which formed the basis of electrochemistry. He gave popular names to many important terms in chemistry, such as anode, cathode, electrode and ion.

182 1 year, Faraday completed the first major electrical invention. Two years ago, Oster discovered that if there is current in the circuit, the magnetic needle of the ordinary compass near it will shift. Faraday was inspired by this and thought that if the magnet was fixed, the coil might move. According to this idea, he successfully invented a simple device. In this device, as long as there is current passing through the wire, the wire will keep rotating around the magnet. In fact, Faraday invented the first motor, the first device to use electric current to move objects. Although this device is simple, it is the ancestor of all motors in the world today. This is a major breakthrough. However, its practical use is still very limited, because there is no other way to generate electricity except simple batteries. As we all know, a stationary magnet will not generate current in nearby lines. 183 1 Faraday found that when the first magnet passes through the closed circuit, there will be current in the circuit, and this effect is called electromagnetic induction. It is generally believed that Faraday's law of electromagnetic induction is one of his greatest contributions. Two reasons are enough to show that this discovery can go down in history. First, Faraday's law is more important for understanding electromagnetism theoretically. Secondly, as Faraday demonstrated with his first generator (Faraday disk), electromagnetic induction can be used to generate continuous current. Although modern generators supplying power to towns and factories are much more complicated than those invented by Faraday, they are all made according to the same electromagnetic induction principle. It was Faraday who introduced the important concepts of magnetic lines and wires into physics. By emphasizing the "field" between them instead of magnets, he opened the way for many advances in contemporary physics, including Maxwell's equations. Faraday also found that if polarized light passes through a magnetic field, its polarization will change. This discovery is of special significance, indicating for the first time that there is a certain relationship between light and magnetism. Faraday's life is great, Faraday is ordinary. He is very keen on the popularization of science. Shortly after he became the laboratory director of the Royal Institute, he launched a seminar on Friday night and a Christmas youth science lecture. He gave a speech at more than 65,438+000 Friday evening seminars and gave a speech at the Christmas Youth Science Lecture in 19. His popular science lectures are simple and easy to understand, with rich demonstration experiments, which are very popular. Faraday is also keen on public utilities and has served many public and private institutions in Britain for a long time. He is simple, unsociable, does not seek fame and fortune, and likes to help relatives and friends. In order to concentrate on scientific research, he gave up all high-paying business jobs. 1857, he declined the nomination of the Royal Society to elect him president. He is willing to fulfill his commitment to science as a civilian and work in the laboratory of the Royal Academy of Sciences for life, becoming an ordinary michael faraday.

1On August 25th, 867, michael faraday, a civilian, died peacefully in his study. A generation of scientific superstars passed away after writing his extraordinary life and leaving priceless wealth for mankind.

1-2 electromagnetic induction experiment

Looking back on Faraday's experiment, it is not difficult to operate the experiment of magnetic power generation. The electromagnetic induction phenomenon can be demonstrated by the following experiment: 12 1, where 1 is a permanent magnet, 2 is a coil and 3 is a demonstration vibrating mirror. The coil forms a closed loop through the galvanometer. When the magnet is inserted into the coil, the ammeter pointer deflects; When the coil of the permanent magnet does not move, the pointer does not move; When the magnet is pulled out, the pointer deflects in the opposite direction. This experiment shows that when the magnetic flux passing through the closed coil changes, it does produce induced current. Study on the conditions of induced current generation by experimental method

Experimental method: the magnetic field is static and the conductor moves downward; Command to move left or right.

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Teachers' research concluded that when a part of the conductor in the closed circuit moves to cut the magnetic induction line, there will be current in the circuit. Understand the meaning of "conductor movement cuts the magnetic induction line": the movement of cutting the magnetic induction line means that the direction of the movement speed of the guide body is not parallel to the direction of the magnetic induction line. When the conductor does not move, will the magnetic field move and will there be current in the circuit? We can continue to do experiments.

In the experiment, the bar magnet was inserted into the solenoid and pulled out from the solenoid. Note: When the magnetic bar is plugged and unplugged, the bent magnetic induction line is cut off, and there is induced current in the circuit. It can be concluded that no matter whether the conductor moves or the magnetic field moves, as long as there is relative movement between the conductor and the magnetic field to cut the magnetic field lines, there will be current in the closed circuit. When some conductors in a closed circuit cut magnetic field lines, the number of magnetic field lines passing through the circuit will change. If there is no relative motion between the conductor and the magnetic field, will there be current in the circuit?

Connection and disconnection of coil circuit. The sliding blade of the sliding rheostat slides left and right. At this time, the galvanometer pointer deflects, indicating that there is induced current.

On the basis of observing the experimental phenomena, pay attention to analyze the physical process of the above phenomena: because the magnetic induction intensity B of the magnetic field excited by current is always proportional to the current intensity I, that is, B ∝ i. The closing or opening of the circuit controls the change of current from scratch or from scratch; A rheostat changes the current by changing the resistance. The change of current will inevitably lead to the change of magnetic field in the closed loop, and the number of magnetic induction lines passing through the closed loop will also change-when the magnetic flux changes, current will be generated in the closed loop. When the S in the circuit is opened and closed, the magnetic field passing through the closed circuit changes: whether the conductor cuts the magnetic induction line or the magnetic field changes, the magnetic flux passing through the closed circuit will actually change.

1-3 analysis and summary experiment

It can be seen from the above 2- 1 experiment 1 that as long as the conductor cuts the magnetic induction line, the induced current will be generated in the closed coil. At this time, it can be seen from experiment 3 that the wire did not cut the magnetic induction line obviously, but the magnetic flux in the coil changed. At this time, looking back at experiment 1 and experiment 2, we can analyze the factors that change the magnetic flux: φ = b sin θ, ① when the magnetic induction intensity b changes; ② the area s of the coil changes; ③ The included angle θ between the magnetic induction intensity B and the area S changes. All three situations will lead to the change of magnetic flux. The condition of induced current is that the magnetic flux passing through the closed circuit changes. The key words to pay attention to here are "off" and "change". That is to say, there is a magnetic flux passing through the closed circuit but it does not change. Even if the magnetic field is strong and the magnetic flux is large, no induced current will be generated. Of course, if the circuit is not closed, it is impossible to generate current.

Can guide students to sum up: 1. No matter what method is used, as long as the magnetic flux passing through the closed loop changes, there will be current in the closed loop. This phenomenon of using magnetic field to generate current is called electromagnetic induction, and the generated current is called induced current.

Generation conditions of induced current.

The circuit must be closed;

(2) the change of magnetic flux.

As can be seen from the above analysis, the analysis of the above experiments has typical significance. The analysis of the above experiments can be regarded as some manifestations of inquiry learning.

2 my teaching suggestions

The author has been engaged in high school teaching for many years and has some superficial understanding of this part. To understand and apply Faraday's law of electromagnetic induction, students should pay attention to the following problems in teaching.

2- 1 The three concepts of magnetic flux, magnetic flux change and magnetic flux change rate should be strictly distinguished. Regarding the difference between these three concepts, my approach is to ask the students whether there is induced current when the magnet is put into the coil in the experiment of1-2. At this time, the magnetic flux is the largest, but there is no induced current. The erroneous statement that the magnetic flux is large and the induced current is large is denied. Then I quickly put it in the coil and then slowly put it in the coil. At this time, the induced current is one big and one small. The analysis is as follows: all coils are put in from the same place outside, and the change of magnetic flux is the same. It is also denied that the change of magnetic flux determines the magnitude of induced current. Therefore, the analysis shows that the faster the magnetic flux changes, the greater the change rate and the greater the induced current.

2-2 It is concluded that there are generally three situations to find the change of magnetic flux: when the loop area is constant, the magnetic induction intensity changes (as in Experiment 2); When the magnetic induction intensity is constant and the loop area changes (for example, experiment1); When the loop area and magnetic induction intensity are unchanged, but their relative positions change (such as rotation),

2-3 E is the average electromotive force over a period of time, which is generally not equal to the average of the instantaneous values of initial and final induced electromotive force.

2-4 Note that the change rate of magnetic flux in Faraday's law of electromagnetic induction given in the textbook takes the absolute value, and the induced electromotive force also takes the absolute value, which indicates the magnitude of the induced electromotive force and does not involve the direction.

Formula 2-5 is an important formula to express the magnitude of induced electromotive force when the conductor moves to cut the magnetic induction line. Let the students know that it is a special form of Faraday's law of electromagnetic induction, which is convenient to use when the conductor moves to cut the magnetic induction line. It should be noted that the directions of B, L and V must be perpendicular to each other, and the vertical component should be taken in the case of non-perpendicular.

It is suggested that in specific teaching, teachers should help students form a knowledge system, so as to deepen their understanding of the concepts and principles they have learned and help students understand and master new concepts and principles. In the teaching of Faraday's law of electromagnetic induction, the following contents are related to the previous knowledge. I hope the teacher can pay attention to it in teaching.

From the knowledge of "constant current", it can be known that there must be electromotive force in the closed circuit to make holding current continuous; In the electromagnetic induction phenomenon, if there is induced current in the closed circuit, there must be corresponding induced electromotive force, which leads to the determination of induced electromotive force.

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