2020 Senior High School Physics Alternating Current Teaching Plan 1
Teaching objectives
Knowledge and skills
1. Make students understand the generation principle of alternating current and know what neutral surface is.
2. Master the changing law and representation of alternating current.
3. Understand the instantaneous value and maximum value of alternating current and the exact meaning of neutral surface.
(2) Process and method
1. Master three basic methods of describing physical quantities (text method, formula method and image method).
2. Cultivate students' observation ability, spatial imagination ability and the ability to transform stereoscopic images into plane images.
3. Cultivate students' ability to use mathematical knowledge to solve physical problems.
(3) Emotion, attitude and values
Through experimental observation, we can stimulate learning interest, cultivate good study habits, and realize the importance of using mathematical knowledge to solve physical problems.
Teaching emphases and difficulties
Emphasis: analyze the physical process of alternating current.
Difficulties: the changing law of alternating current and its application.
Teaching methods: demonstration, analysis and induction.
Teaching AIDS: hand-cranked single-phase generator, small light bulb, oscilloscope, multimedia teaching courseware, large ammeter for teaching.
Class type: new teaching
Class plan: 1 class hour
teaching process
(A) the introduction of new courses
Show the single-phase alternator and guide students to observe its main structure first.
Demonstration: the hand-cranked generator model and the small light bulb form a closed circuit. What is observed when the wireframe rotates rapidly?
This kind of current whose magnitude and direction change periodically with time is called alternating current.
New lesson.
1, generation of alternating current
Why can a rectangular coil rotate at a uniform speed in a uniform magnetic field to generate alternating current?
The multimedia courseware prints out the following picture. When the abcd coil rotates around the OO ′ axis in a magnetic field, which side cuts the magnetic induction line? Ab and cd.
When ab moves to the right and cd moves to the left, the induced current in the coil flows in the direction of A → B → C → D → A ..
When ab moves to the left and cd moves to the right, what is the direction of induced current in the coil?
The induced current flows in the direction of D → C → B → A → D
When the plane of the coil is parallel to the magnetic induction line, the speed direction of ab side and cd side is perpendicular to the magnetic induction line, that is, the magnetic induction line is cut vertically on both sides, and the induced electromotive force is the maximum.
When the coil turns to what position, the induced electromotive force is the smallest?
When the coil plane is perpendicular to the magnetic induction line, the speed directions of ab side and cd side are parallel to the magnetic induction line, that is, the magnetic induction line is not cut and the induced electromotive force is zero.
Use multimedia courseware to print the concept of neutral surface on the screen;
(1) neutral surface-the position where the plane of the wireframe is perpendicular to the magnetic induction line.
(2) When the coil is in the neutral surface position, φ passing through the coil is the largest, but =0.
(3) When the coil passes through neutral surface, the direction of I induction in the coil will change. When the coil rotates once, the direction of the induced current will change twice.
2. The changing law of alternating current
Let the coil plane rotate from neutral surface, and the angular velocity is ω. After time t, the rotation angle of the coil is Ω t, and the included angle between the direction of the ab side line speed V and the direction of the magnetic induction line is also equal to Ω t, as shown in the right figure. Let the side length of ab be L 1, the side length of bc be L2, and the magnetic induction intensity be B. What is the induced electromotive force generated by the side of ab?
eab = bl 1 vsinωt = bl 1ωsinωt = bl 1 L2 sinωt
What is the induced electromotive force in the whole wireframe at this time?
e=eab+ecd=BL 1L2ωsinωt
If the coil has n turns, it is equivalent to n identical power supplies connected in series, e = nbl1L2 Ω sin Ω t, so that em = nbl1L2 Ω is called the peak value of induced electromotive force, and e is called the instantaneous value of induced electromotive force.
According to ohm's law of some circuits, the maximum value of voltage Um=ImR, and the instantaneous value of voltage u = um sin ω t.
2020 Senior High School Physics Alternating Current Teaching Plan II
I. teaching material analysis
The knowledge of alternating current is closely related to production and life, and it is widely used. Considering that high school only briefly introduces the generation, description method and basic law of alternating current, this knowledge is an extension of the electromagnetic induction that has been learned, so it is very beneficial to broaden students' thinking and improve their ability in the teaching process.
In order to adapt to students' acceptance ability, the teaching materials gradually move from perceptual to rational, from qualitative to quantitative. The teaching material first demonstrates the alternating current generated when the rectangular coil rotates at a uniform speed in a uniform magnetic field with teaching AIDS to show how the alternating current is generated, and emphasizes that students should observe the changes of the ammeter pointer when the coil passes through four special positions shown in Figure 5. 1-3. Analyze the changes of electromotive force and current direction, let students have a general understanding of the changes of electromotive force and current, and then let students analyze the directions of electromotive force and current in the coil independently with their right hands. This can fully mobilize the enthusiasm of students and cultivate their ability of observation and analysis.
With regard to the changing law of alternating current, the textbook uses Faraday's law of electromagnetic induction learned in the previous chapter to guide students to deduce, and obtains the expressions of instantaneous value and maximum value of induced electromotive force, and then deduces the expressions of instantaneous value and maximum value of current and voltage according to Ohm's law of closed circuit and Ohm's law of some circuits.
Second, the teaching objectives
1, knowledge target
(1) Know what alternating current is. And understand the generation principle of alternating current, and know what neutral surface is.
(2) Master the changing law of alternating current and its expression method.
(3) Understand the instantaneous value and maximum value of alternating current and the exact meaning of neutral surface.
(4) Know several kinds of common alternating current. Such as sinusoidal alternating current, sawtooth alternating current and rectangular pulse current.
2. Ability objectives
(1) Master three basic methods to describe physical quantities (text method, formula method and image method).
(2) Cultivate students' observation ability, spatial imagination ability and the ability to transform stereoscopic images into plane images.
(3) Cultivate students' ability to solve physical problems with mathematical knowledge.
3. Emotion, attitude and values.
According to the actual situation, cultivate students' idea of integrating theory with practice.
Third, the focus and difficulties in teaching
Key points: 1. Physical process analysis of alternating current.
2. The image description of the changing law of alternating current.
Difficulties: 1, the changing law of alternating current and its application.
2. Understand the one-to-one correspondence between the image and the actual engine speed.
Fourthly, the analysis of learning situation.
Students have studied electromagnetic induction and understand that the cutting magnetic field of a conductor will produce electromotive force. Learning alternating current on this basis is in line with students' cognitive law of understanding. However, this is a new concept. In view of students' different acceptance ability, it is necessary to explain in detail and strengthen guidance. In order to make students accept it more intuitively and stereoscopically, multimedia teaching methods are also adopted.
Teaching methods of verbs (abbreviation of verb)
Demonstration+analysis+induction
1. Through the demonstration of rectangular coil rotating at a uniform speed in a uniform magnetic field, students can combine perspective analysis with side view analysis, and combine special position analysis with arbitrary position analysis to understand the generation principle and variation law of alternating current.
2. Using the method of conductor cutting magnetic field lines to produce I inductance, the variation law of alternating current is analyzed.
Sixth, preparation before class
1. Students' study preparation: Learn some knowledge through preview.
2. Teachers' teaching preparation: making multimedia courseware, previewing learning plans and teaching AIDS before class.
Seven. Class schedule: 1 class hour
Eight, the teaching process
(A) preview the inspection, summing up the doubts
Check and implement students' preview, understand students' doubts, and make teaching targeted.
(2) Scene introduction and display objectives.
Using multimedia courseware to show goals
Show the single-phase alternator and guide students to observe its main structure first.
[Demonstration] The teacher has a generator model in his hand. The generator is connected to the small light bulb for the first time. When the wireframe rotates slowly, the small light bulb does not light up. When the wireframe rotates rapidly, the small light bulb flashes.
The second generator is connected to the teaching galvanometer. When the wireframe rotates slowly (or swings rapidly), the galvanometer pointer swings left and right.
Thinking: What kind of current is generated in the coil?
(Lead the students to answer: This current is the current in our home circuit, and its magnitude and direction change periodically with time. This current is called alternating current. A current whose direction does not change with time is called direct current. Alternating current and direct current can be converted to each other. )
Note: the speed of the teacher's manual generator has changed, one is faster and the other is slower.
Observe the experimental phenomenon and think about why this phenomenon occurs. So as to introduce alternating current.
(3) Cooperative inquiry and intensive teaching.
Why does the rectangular wire frame rotate at a uniform speed in a uniform magnetic field, and alternating current can be generated in the wire frame?
The multimedia courseware prints the following picture.
[Teacher's question] When abcd wireframe rotates around the OO' axis in a magnetic field, which sides are the magnetic induction lines cut?
[answer] ab and cd edge.
[Teacher's question] Where does the wire frame turn to produce the largest induced electromotive force?
[Answer] When the plane of the coil is parallel to the magnetic induction line, the speed direction of ab side and cd side is perpendicular to the direction of the magnetic induction line, that is, the magnetic induction line is cut vertically on both sides. At this time, the induced electromotive force is the largest.
[Teacher] When the wireframe rotates to what position, the induced electromotive force is the smallest?
[Answer] When the plane of the wireframe is perpendicular to the magnetic induction line, the speed directions of ab and cd sides are parallel to the magnetic field lines, that is, the two sides of the magnetic field lines are not cut, and the induced electromotive force is 0.
Use multimedia courseware to print the concept of neutral surface on the screen;
2020 Senior High School Physics Alternating Current Teaching Plan III
Teaching objectives
Knowledge and skills
1. Make students understand the generation principle of alternating current and know what neutral surface is;
2. Master the changing law and expression method of alternating current;
3. Understand the instantaneous value and maximum value of alternating current and the exact meaning of neutral surface.
Process and method
1. Master three methods to describe physical quantities: words, formulas and images;
2. Cultivate students' observation ability and spatial imagination ability;
Emotional attitude and values cultivate students' concept of integrating theory with practice.
Physical process analysis of alternating current.
Variation law of alternating current and its application in teaching difficulties.
teaching process
First, classroom introduction: first observe two demonstration experiments.
Demo 1: 1. Dry battery powered LED. 2. Power the diode with a hand-cranked alternator.
Students observe the light-emitting situation of diodes, indicating that the current provided by generators is changing.
Demonstration 2: 1. Power the sensitive galvanometer with a dry battery. 2. Power the sensitive galvanometer with a hand-cranked alternator.
Students observe the change of the pointer of the sensitive galvanometer and show that the direction of current provided by the motor is changing.
Compare the first and second demonstrations and summarize the differences between AC and DC. Students complete the example 1.
Second, the generation of alternating current.
Question: Why can a generator produce alternating current? Basic structure: magnetic field, coil
Generation conditions: the coil rotates around the axis perpendicular to the magnetic field in a uniform magnetic field.
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