Knowledge target

1, know how the eddy current is generated;

2. Know the disadvantages and benefits of eddy current, and how to prevent and use it;

Affective goal

By analyzing examples, we can cultivate students' comprehensive understanding and scientific attitude towards things.

Teaching suggestion

This course is an elective course, which is a special electromagnetic induction phenomenon and has many applications in practice, such as generators, motors, transformers and so on. So you can choose to attend classes or know what students are reading according to the actual situation. What is eddy current is the key content of this lesson.

Eddy current, like self-perception, has both advantages and disadvantages. We should make full use of these examples in teaching to cultivate students' scientific attitude towards things in an all-round way.

Teaching design scheme

Introduction: Guide students to observe generators, motors and transformers (in kind or in pictures).

Question: Why is their iron core not a whole piece of metal, but made of many thin silicon steel sheets insulated from each other?

Guide the students to read and answer, thus leading to the concept of eddy current: what is eddy current?

When a piece of metal is placed in a changing magnetic field or moves in a magnetic field, it will generate induced current in the metal block and form a closed loop in the metal block, much like a vortex of water, so it is called eddy current.

The resistance of the whole metal is very small, so the eddy current is often very large.

Let the students understand that eddy current is the electromagnetic induction phenomenon of the whole conductor and obeys the law of electromagnetic induction.

Second, what is the practical significance of eddy current?

(1) Why are motors and transformers generally made of thin silicon steel sheets and insulated from each other, so as to reduce the loss caused by eddy currents?

⑵ What are the advantages of high-frequency induction furnace smelting metal?

How to use eddy current principle for electric measuring instruments to facilitate observation?

After asking the above questions, let the students read, discuss and answer.

Homework: Ask the students to go to the physics laboratory in their spare time to observe how the watt-hour meter uses eddy current, and write a short article to explain it.

Chapter Two: Potential Difference and Potential

I. teaching material analysis

(A), the status and role of teaching materials

This section is the content of Section 4 and Section 5 of Chapter 1 of 3- 1 Physics Elective Course of People's Education Society. This section plays a connecting role after the electric field intensity and before the electrostatic phenomenon. From the point of view of electric field doing work on charge, the textbook deduces that the work done by electric field force in uniform electric field has nothing to do with the path of moving charge. The definition of electric potential is given by definition method, and the equipotential surface is described by electric potential, which gives guidance to the improvement of students' ability and the transfer and flexible application of knowledge.

(2) Analysis of academic situation

Students have learned the knowledge of charge, Coulomb's law, electric field intensity and so on, and have a basic understanding of this section, but it is not deep enough and needs to be further cultivated and improved through this section.

(3) Teaching content

This class is the first class, the main content is the introduction of the concept and the understanding of its physical meaning.

Second, the analysis of teaching objectives

According to the requirements and ideas (inquiry, subjectivity, development and harmony) of the overall goal of the new high school curriculum (to further improve scientific literacy and meet the lifelong development needs of all students), the characteristics of this textbook (the integration of ideology, inquiry, logic, methodology and philosophy) and the learning foundation of the students (knowledge structure, thinking structure and cognitive structure), the teaching objectives of this course are:

Knowledge and skill goal: 1. Understand the concept of potential, know that potential is a physical quantity describing the energy properties of electric field, understand that potential difference has nothing to do with the position of zero potential plane, and skillfully apply its concept and define UAB? WAB performs correlation calculation q

Count. Make clear the relationship among potential difference, electric potential, electrostatic force work and electric potential energy. 2. Understand that electric potential is a physical quantity describing electric field, and know the relationship between electric potential and potential difference, which is related to the choice of zero potential surface, and know the change of electric potential along electric field lines in electric field.

Process and Methods Purpose: To use the knowledge that students have mastered to make analogy and generalization, to tell new knowledge, and to cultivate students' self-study ability and abstract thinking ability. Combined with the previous knowledge, we can understand the relationship between electric potential energy and electrostatic force to do work, so as to better understand the concepts of potential difference and potential.

Emotion and values goal: Try to use physics principles and research methods to solve some practical problems related to production and life, and enhance the values of scientific inquiry.

Third, the analysis of important and difficult points

In order to better achieve the teaching objectives, the teaching focus of this course is to understand and master the concepts and significance of potential difference, potential and equipotential surface. Before studying in this section, the students have learned other forces to do work, such as the change of molecular potential energy when molecular force does work and the change of elastic potential energy when spring elasticity does work. Therefore, the difficulty of teaching in this section is to distinguish and link potential and potential surface with contextual knowledge, so as to solve related problems.

Fourth, analysis of teaching methods

(A), learning guidance

The main aspect of teaching contradiction is students' learning. Learning is the center and learning is the purpose, so we should constantly guide learning in teaching.

Students study. Modern education pays more attention to the guidance of students' learning methods in the teaching process. Physics teaching is based on experiments and pays attention to inspiring thinking and teaching methods. For simple harmonic motion's rich perceptual knowledge, in teaching, we should collect some examples from simple harmonic motion, skillfully use questions, evaluate and activate students' enthusiasm, mobilize the classroom atmosphere, and let students complete their learning tasks in a relaxed, independent and discussed learning environment. Finally, let the students speak freely, and give some examples of simple harmonic motion in life, so that it can go from practice to theory and then from theory to practice.

(2) Analysis of teaching methods

The guiding ideology of this course design is: modern cognitive psychology-constructivism learning theory.

Constructivist learning theory holds that learning should be regarded as students' active constructive activities, and students should be related to a certain knowledge background, that is, the situation. Learning in the actual situation can make students assimilate and index the new knowledge they want to learn by using the existing knowledge and experience, so that the acquired knowledge is not only easy to keep, but also easy to migrate to unfamiliar problem situations.

This course adopts the teaching method of "induced thinking and inquiry", vividly and intuitively displays the teaching content by using the projector, guides students to discover the laws and description methods of harmonic vibration, and leaves students with the opportunity to analyze problems.

Teaching process of verbs (abbreviation of verb)

The teaching design of this course fully embodies the students' development-oriented, cultivating students' abilities of observation, generalization and inquiry, following students' cognitive laws, and embodying the teaching principles of integrating theory with practice, teaching students in accordance with their aptitude and step by step. Stimulate students' interest by creating problem situations, which means that in the process of exploring and solving problems, students move from learning to learning, and from passively answering questions to actively exploring.

1, knowledge review. First of all, show the picture. The electric field has a powerful effect on the charge put into it, and so does the internal charge of this conductor.

Force can do work, so electric field also has the nature of energy.

The concepts of electric potential and potential difference are abstract. By introducing the related concepts of gravity field for analogy, the perceptibility of knowledge can be enhanced and students can understand them. Then review the knowledge about work and the relationship between gravitational work and gravitational potential energy. Measurement of work: w? FScos？ ; The work done by gravity is only related to the position, not to the path; Relationship between gravitational work and potential energy: gravitational potential energy is relative and has a zero potential energy surface.

Further guide students to expand their thinking, review what they have learned and become interested in new knowledge. For example, we have also studied other forces to do work, such as molecular force to change molecular potential energy, spring force to change elastic potential energy, so what is the situation of electric field force to do work?

2. Introduce new courses.

It is pointed out that in the electric field formed by charge +Q at a certain point, when the same charge is put into points A and B at different positions of the electric field, the electric field force is different. This is because the electric field intensity at point A and point B is different. In order to study the problem conveniently, take the uniform electric field as an example. In a uniform electric field, the charge moves from point A to point B, and the magnitude of the electric field force is f?

EQ is constancy, then electricity.

The magnitude of the work done by the field force is: w? EqScos？ . Here it is, w

Just like gravity does work

So, w Escos? Is a quantity that has nothing to do with the charge itself. hcos？ , is also a physical quantity that has nothing to do with the object itself, only related to the nature of the gravity field itself. This ratio is called the potential difference between point A and point B and is expressed by UAB.

Continue to contact gravity potential energy to ask questions: the greater the height difference of an object moving under the action of gravity, the greater the change of gravity potential energy. Height difference is height difference, and potential difference is potential difference. So how to define the potential of each point in the electric field? After giving the students a minute to think, guide them to read the definitions in the textbook, UAB? WAB, if the potential at point B is defined as zero electricity Q.

Potential point, the potential of point A is equal to the work done when the unit positive charge moves from point A to point B-zero potential point. So the teacher stressed, usually use potential? It means that the potential at a certain point in the electric field is equal to the work done by the electric field force when the unit positive charge moves from that point to the reference point (zero potential point).

3. Strengthen and extend knowledge points.

Guide the students to think, and point out that the potential difference has nothing to do with the choice of zero potential, and the potential is related to the choice of zero potential relative to zero potential. Then the class gives a few minutes, and the students independently complete an example: setting AB in the electric field.

2 potential difference between two points u? 2.0? 10V, q of charged particles? 1.2? 10? 8C, move Q from point A to point B,

How much work did the electric field force do? Is it positive or negative? Set UA? UB .

4. Summary of knowledge. (1), the potential difference between two points in the electric field, similar to the height difference between two points in the gravity field, the potential difference UAB? WAB asked

U has nothing to do with w and q (2) What is the potential at a certain point in the electric field? , which is equal to the work done by the electric field force when the unit positive charge moves from this point to the reference point. Note that the potential has nothing to do with the choice of the reference point. (3)、UB？ b，A？ A

Along the electric field line, the potential is getting lower and lower.

5. assign homework. Assign exercises after class and ask students to complete them independently after class.

Chapter III: Uniform Circular Motion

First, the analysis of teaching tasks

Uniform circular motion is the first curve motion to be learned after linear motion. It is how to describe and study the extension of motion that is more complicated than linear motion, is the further extension of the knowledge of the relationship between force and motion, and is the basis for learning other more complicated curvilinear motions (flat throwing motion, simple pendulum simple harmonic motion, etc.). ) in the future.

Learning uniform circular motion needs to be based on uniform linear motion, Newton's law of motion and other knowledge.

Starting with observing the phenomena in life and experiments, students can understand the conditions for objects to move in a curve, draw the conclusion that uniform circular motion is the most basic and simple circular motion, and experience the scientific research method of establishing an ideal model.

By setting the situation, students can feel the different speeds of circular motion, and realize the need to introduce physical quantities to describe the speed of circular motion, and then learn the concepts of linear velocity and angular velocity by analogy with uniform linear motion and multimedia animation.

Through group discussion, experimental inquiry and mutual communication, a platform is created for students to discuss and analyze several practical problems according to the knowledge learned in this class, so as to mobilize students' learning emotions, learn to cooperate and communicate, and cultivate rigorous and pragmatic scientific quality.

Through life examples, we know that circular motion is everywhere in life, and it is very necessary and important to study and study circular motion, which can stimulate learning enthusiasm and interest.

Second, the teaching objectives

1, knowledge and skills

(1) Know the conditions under which an object moves on a curve.

(2) Understanding circular motion; Understand uniform circular motion.

(3) Understand the linear velocity and angular velocity.

(4) Calculate the linear velocity and angular velocity in practical problems and judge the direction of linear velocity.

2. Process and method

(1) Through the formation of the concept of uniform circular motion, we know the physical method of establishing an ideal model.

(2) Understand the application of analogy by learning the definitions of uniform circular motion, linear velocity and angular velocity.

3. Attitudes, emotions and values

(1) Understand the universality of circular motion and the necessity of learning circular motion from life examples, and stimulate learning interest and curiosity.

(2) Through the learning process of discussing and communicating with each other, I understand the important role of cooperation and communication in learning. I am willing to cooperate with others in activities, respect the opinions of my classmates and be good at communicating with others.

Third, the focus and difficulties in teaching

Key points:

The concept of (1) uniform circular motion.

(2) Linear velocity and angular velocity are used to describe the speed of circular motion.

Difficulties: Understand that the linear velocity direction is the tangent direction of each point on the arc.

Fourth, teaching resources.

1. Equipment: wall clock, pull-back toy trolley, turntable with holes on the side, glass plate, yellow sand for building, table tennis, inclined plane, scale, and small balls connected with strings.

2. Courseware: flash courseware-demonstrating uniform circular motion with different arc lengths at the same time; —— Demonstrate uniform circular motion with two motion radii rotating at different angles at the same time.

3. Video: The process of the three-ring roller coaster.

Five, teaching design ideas

This design includes three parts: the conditions for the object to do curvilinear motion, uniform circular motion, linear velocity and angular velocity.

The basic idea of this design is: on the basis of video and experiment, the conditions for the object to move in a curve are obtained through analysis; Through observation and comparison, the characteristics of uniform circumference are summarized. Based on the different descriptions of uniform circular motion speed by situational awakening, the concepts of linear velocity and angular velocity are introduced through discussion, questioning, activity and communication, so as to consolidate the learned knowledge and solve practical problems by using the learned knowledge.

The key points of this design are: the concept of uniform circular motion and the concepts of linear velocity and angular velocity. The method is as follows: by observing and comparing two kinds of circular motions of clock hands and roller coaster, the characteristics of uniform circular motion are summarized; Set the dialogue scene between the earth and the moon, and introduce the description of uniform circular motion speed; Then, with the help of multimedia animation, the concepts of uniform circular motion, linear velocity and angular velocity are obtained by analogy with uniform linear motion.

The difficulty of this design is: the direction of linear velocity. The method is: two demonstration experiments, observing the ball flying in a circular motion along the tangent line and the trajectory distribution of red ink flying on paper from the edge of the rotating turntable, are displayed intuitively.

This design emphasizes taking video, experiment and animation as clues, focusing on stimulating students' senses, emphasizing students' experience and feelings, transforming abstract thinking into image thinking, teaching concepts and laws embody physical methods such as "modeling" and "analogy", and students' activities focus on discussion, communication and experimental exploration, and the issues involved are linked to real life, close to students' life, emphasizing the perception of learning value and significance.

It takes about 2 class hours to complete the design.

Sixth, the teaching process.

1, teaching flow chart

2, flow chart description

Scene 1 Video, Presentation, Question 1

Play the video: Three-ring roller coaster, let students see that the movement of objects has straight lines and curves.

Demonstration: Let the students blow hard on the table tennis ball that moves in a straight line and experience the situation under which the ball will move in a curve.

Question 1: Under what circumstances will an object move in a curve?

Situation 2 Observation, Comparison and Questioning 2

Observe and compare two kinds of circular motion: clock hands and roller coaster.