Exploring the relationship between current and voltage resistance: lecture notes 1 I. teaching materials
The arrangement of this lesson is arranged after students have learned the concepts of current, voltage and resistance, as well as the use of voltmeter, ammeter and sliding rheostat. It not only conforms to the students' understanding rules from easy to difficult, from simple to complex, but also maintains the structural and systematic knowledge. Through the study of this course, students can master the relationship between the three basic quantities of electricity in the same circuit, understand the experimental method of using the "control variable method" to study the relationship between multiple variables, and also pave the way for studying electric work and electricity in the future. Ohm's law is a law summed up through experimental exploration. It is very logical and theoretical, and the experiment is also difficult, especially for students in experimental design and data analysis. Therefore, teachers should do a good job of timely guidance and appropriate guidance. By learning Ohm's law and experiencing the process of experimental inquiry, we can understand the scientific inquiry method of "control variable method", understand the universality and importance of this method in experimental inquiry, and experience the fun of scientific inquiry, so as to form a scientific attitude of respecting facts and exploring truth.
Second, students.
The characteristics of junior high school students' understanding of things are: they begin to transition from concrete image thinking to abstract logical thinking, but thinking is often directly related to perceptual experience. Before learning this knowledge, students have already understood the concepts of current, voltage and resistance, and initially learned the use of voltmeter, ammeter and sliding rheostat, but they are all single skill operations without comprehensive application. The understanding of the relationship between current, voltage and resistance is superficial and incomplete, and it has not risen to rational understanding.
Third, talk about teaching objectives.
According to the requirements of compulsory education physics curriculum standards and the actual situation of students, I design to divide this class into two classes. The first class is about the process and conclusion of experimental inquiry, and the second class is about formulas and their simple calculations. The teaching objectives of this lesson are:
Knowledge and skills
1, will use experiments to explore the relationship between current, voltage and resistance;
2, will use voltmeter and ammeter to measure the voltage and current at both ends of the conductor;
3, will use sliding rheostat to change the voltage at both ends of some circuits;
4. Understand the content of Ohm's law.
(2), process and method
1, so that students can understand the idea of studying physical laws by controlling variables.
2. Further cultivate students' ability to operate electrical experiments and analyze and summarize conclusions according to experimental results.
(C), emotional attitudes and values
Stimulate students' interest in learning through the process of inquiry. Cultivate students' scientific attitude of seeking truth from facts and the habit of studying hard.
Teaching emphasis: master experimental methods; Understand the relationship between current and voltage and resistance.
Teaching difficulty: analyze and summarize the experimental data and draw a conclusion.
teaching method
Heuristic comprehensive teaching method based on experimental inquiry.
Fourth, talk about the teaching process:
First, create an environment to stimulate and explore ideas.
Through the experiment of the desk lamp with adjustable brightness at home, guide the students to observe the experimental phenomena carefully, exchange and discuss, design a simulation experiment with the equipment at hand, let two students take the stage to do it, and then explain it after finishing, and get the reason why the brightness of the dimming desk lamp changes. In this way, through students' hands-on experiments, they have exercised their thinking ability and operation ability, paved the way for future experimental methods, fully exerted their autonomy and creativity, and stimulated their thirst for knowledge. It fully embodies the basic idea of moving from life to physics and from physics to society.
Second, carry out inquiry activities and conduct in-depth research and practice.
(1) Using FLASH and students' small experiments, it is concluded that current is related to voltage and resistance. Theme on the blackboard: exploration-the relationship between current, voltage and resistance
(2), guess and hypothesis
Students discuss in groups. At this time, students' imagination will be colorful. Teachers should give students opportunities to exchange guesses, be more sure, encourage and guide. Finally, send representatives to report to the whole class, and other groups can also supplement them appropriately. Guide the students to complete the questions 1 and 2 according to their guesses. This can not only cultivate students' cooperative consciousness, but also exercise their language expression ability.
(3) Design circuit diagram
Step by step, guide students to analyze the experimental equipment and the connection mode of the equipment through the prompt questions on the slide, and design the circuit diagram on this basis. This experiment is a comprehensive quantitative experiment, which uses a lot of equipment. In addition to voltmeter and ammeter, it is difficult for students to adjust the circuit with sliding rheostat. This requires real-time guidance from teachers, so that students can fully express their opinions and finally form a unified circuit diagram.
(4) Students experiment in groups and teachers patrol.
Let the students explore their own guesses, because this is what he is eager to verify. Of course, he can also explore these two experiments. Connecting circuits is a basic skill that students should master, but it is the first time that so many devices are connected together. A variety of guidance methods can be used to educate students to connect orderly, which can be connected in series first and then in parallel. On this basis, complete the fourth question of the study plan. Emphasize that each inquiry should be done at least three times, so that the conclusion can be universal. Educate students to respect facts and never leave data blank or fabricate data. Interspersed with the story of Mr. He Runwei, deputy head of the Physics Group of China Basic Education Curriculum Reform Group, in the United States, to stimulate students' national self-esteem and realize the importance of experiments.
(5) Collect evidence, analyze and draw a conclusion.
One group of students write their own experimental data, and the other group of students check and correct them, eliminate bad values, guide students to analyze the data, find out the relationship between the data and draw conclusions. Exchange research results and make timely adjustments and corrections. At this stage, students' knowledge will leap from perceptual knowledge to rational knowledge under the guidance of teachers, and students' emotions will be sublimated in interaction.
(vi) Evaluation and communication
The purpose is to guide students to analyze experimental errors, realize the existence of errors, and develop a scientific attitude of seeking truth from facts.
Third, the class summary
Let the students recall the process of exploring the experiment, answer the harvest of this lesson and consolidate the knowledge they have learned.
Fourth, classroom exercises: aimed at further consolidating the ideas and conclusions of controlling variables.
Verb (abbreviation for verb) extracurricular activities
Collect Ohm's life information online and exchange feelings. Stimulate students to learn the scientific spirit of scientists who study hard and explore boldly.
blackboard-writing design
Discussion on the Relationship among Current, Voltage and Resistance
Resistance r = ω
Voltage current current current.
Voltage u = v
Resistance r/ω current I/A
Table 1 Table 2
The current in a conductor is directly proportional to the voltage across the conductor and inversely proportional to the resistance of the conductor.
Exploring the relationship between current and voltage resistance, handout 2, textbook
1, the position and function of teaching materials
The content of this lesson is based on students' study of concepts such as circuit, current, voltage and resistance, and mainly explores the quantitative relationship among current, voltage and resistance in electricity. As long as students master this knowledge, they will naturally learn Ohm's Law and its application in the next class, so the content of this class not only plays a connecting role, but also is the key for students to understand and master Ohm's Law.
2. Teaching objectives
(1) Knowledge and skills: Through experimental exploration, obtain and understand the quantitative relationship among current, voltage and resistance; Both ammeter and voltmeter are used to measure the voltage across the conductor and the current in the conductor. Sliding rheostat will be used to change the voltage on some circuits; Through the whole inquiry activity, students' inquiry ability, innovative design ability, operation ability, analysis ability and comprehensive induction ability are improved.
(2) Process and method: Through the inquiry process, further experience, understand and learn the methods of scientific inquiry; Understand the idea of studying physical laws with the research method of "control variables" and learn to study physical problems with images.
(3) Emotional attitude and values: cultivate students' scientific attitude of seeking truth from facts in the process of collecting and processing data; Through inquiry, we can reveal the laws of physics and let students have fun in exploring the unknown world. Pay attention to students' understanding of the objectivity, universality and scientificity of physical laws, and pay attention to the formation of students' scientific world outlook.
3. Emphasis and difficulty of the textbook.
The focus of this lesson is to explore the process of quantitative relationship between current, resistance and voltage, and to master the relationship between them. It is difficult for students to design experiments, conduct experiments, analyze and demonstrate in the process of inquiry.
Second, talk about learning.
Junior two students are curious and eager to learn, but they lack perseverance and the ability to explore and study problems. Therefore, teachers should guide students to acquire new knowledge and develop abstract thinking ability through theoretical analysis and reasoning. Of course, in this process, we should rely on some perceptual knowledge, enhance the intuition and visualization with the help of experiments, let students understand and master, and help them gradually become mature and successful.
Three. Oral English teaching methods and learning methods
This course adopts a variety of teaching methods, such as goal-oriented learning, students' grouping experiments, analysis and discussion, lectures and multimedia demonstrations, which fully embodies the leading role of teachers and students in the classroom in modern teaching, allowing students to actively participate in activities and use their brains in activities, so as to master knowledge and improve their various abilities. Students' main learning methods are experimental inquiry and discussion and induction.
Fourth, talk about the teaching process
Teaching should be based on the method of studying physical problems, centered on mastering knowledge, oriented on cultivating ability, highlighting key points and breaking through difficulties. The specific design is as follows:
1, the introduction of new courses
Learning comes from thinking, thinking comes from questioning, so I demonstrated the schematic diagram of "a small light bulb and a switch in series in the circuit" with multimedia, and then put forward the question "What can you do to change the brightness of the small light bulb". Let the students discuss and analyze actively first, then affirm the students' various methods, and introduce the topic "the relationship between the current in the conductor and the voltage at both ends of the conductor and the resistance of the conductor", which will pave the way for the students to further design experiments and connect circuits.
Step 2 teach new lessons
Any scientific conclusion and physical laws can't be separated from experiments, which are intuitive and vivid, easy to arouse students' curiosity and interest. This section of the textbook arranges a relatively complete inquiry activity, covering seven elements of inquiry.
(1) Ask questions-According to the introduction of the topic, let the students know the content and purpose of this lesson.
(2) Guide students to guess and assume. According to the students' discussion and analysis in the process of introducing the subject, it is not difficult for students to draw the conclusion that "the greater the voltage across the conductor, the greater the current in the conductor;" The greater the resistance of the conductor, the smaller the current in the conductor ",so that students can understand that practice is the only criterion for testing truth. To know whether the guess is correct, we must get a lot of data through experiments and analyze the data carefully before we can sum it up.
(3) Experimental design and experiment.
Before this class, students have already had a certain foundation to explore physical problems by using the "control variable method" (for example, using the "control variable method" to explore the factors affecting the pitch of stringed instruments and the evaporation rate of liquid in experiments). Because there are two reasons that affect the change of current: voltage and resistance, students will naturally think of using the "controlled variable method" to explore the problem. The content of this inquiry is completed in two times.
First, explore the relationship between current and voltage in the conductor.
A) The teacher projects and asks "How to study the relationship between current and voltage?" Ask the students to discuss and analyze the equipment, steps and circuit diagram needed for the experiment. The teacher can add "How to change the voltage across the resistor?" Guide students to answer method 1: change the power supply voltage; Method 2: Using sliding rheostat to change the voltage at both ends of the resistor requires students to compare the difficulty of the two methods and make a reasonable choice. At the same time, it also reminds students that considering the universality and scientificity of physical laws, when studying the relationship between current and voltage, it is necessary to change the fixed resistance and conduct repeated experiments.
B) students do experiments.
Because of the high comprehensive requirements of this section and the difficulty of experimental exploration, I projected the correct experimental circuit diagram on the screen, asked students to connect the physical diagram according to the circuit diagram, and gave friendly tips of "When connecting the circuit, the switch must be turned off" and "Before closing the switch, the slider of the sliding rheostat should be moved to the position with the largest resistance of the connected circuit". When students do experiments in groups, there will be special guidance to help them eliminate possible circuit faults, correct mistakes in the experiments and complete the experiments.
Second, explore the relationship between current and resistance in conductor.
The method is the same as above, but in this experiment, how to keep the voltage constant is the key to success. Students may consider that it is difficult to adjust the voltage with sliding rheostat while keeping the power supply voltage unchanged, and it is also a difficulty to adjust the voltage with sliding rheostat. The key to break through this difficulty is that teachers should guide students to make tentative adjustments, so as to get the correct experimental methods.
(4) Analysis and demonstration
Guide students to reflect the recorded experimental data on coordinate paper by tracing points, so that students can find the information provided by the image: it is not difficult to find that the U-I image is a straight line passing through the origin from the image, and guide students to find out the relationship between the current in the conductor, the voltage at both ends of the conductor and the conductor resistance by using the mathematical knowledge they have learned. Using images to process experimental data can make the data concrete and visualized, which is convenient for students to observe and learn. It can also help students to further understand how to use mathematical tools to study physical problems and understand that disciplines do not exist in isolation, but are interrelated and infiltrated with each other, thus promoting the balanced development of students.
(5), evaluation and communication
"Is your experimental design reasonable?" "Do you have any other design methods?" "Did you encounter any difficulties and troubles during the experiment? How did you overcome or solve it? " "Is your measurement data reliable?" "What is the conclusion of your experiment?" Through a series of questions and students' answers, timely exchange of feedback, timely comments and timely correction can help students sort out the mess, deepen their understanding, and help students form a knowledge structure and consolidate their memories. At the same time, through evaluation and communication, give full play to students' initiative, learn from each other, learn from each other's strengths, improve together, discover their own shortcomings in time and constantly reflect on themselves, and cultivate students' rigorous scientific attitude.
3. Feedback and integration
Because the inquiry process in this class is difficult, it is not easy for students to draw a correct inquiry conclusion smoothly, so I think the consolidation exercise can be left to the next section "Ohm's Law and its Application". What needs to be emphasized is the basic steps of physical inquiry, the method "control variable method" used in the inquiry process, the image method used in analyzing data, and the experimental conclusion that "the current in a conductor is directly proportional to the voltage at both ends of the conductor and inversely proportional to the resistance of the conductor".
4. Blackboard design (projection)
7, 1 Explore the relationship between the current on the resistor and the voltage across it.
First, explore the relationship between current and voltage in the conductor.
1, experimental circuit diagram (omitted)
2. Friendly reminder: "When the circuit is connected, the switch must be turned off." "Before the switch is turned off, the sliding vane of the sliding rheostat should be moved to the position where the resistance of the connected circuit is the largest."
3, record the experimental data table (omitted)
4.U-I relation image
5. Experimental conclusion (omitted)
Second, explore the relationship between current and resistance in conductor.
1, experimental circuit diagram (omitted)
2, record the experimental data table (omitted)
3.R-I relation image
4. Experimental conclusion (omitted)
Step 5 assign homework
Complete the experimental report.