Physics lesson summary “Ohm’s Law for a section of a circuit”; 8th grade

Methodological development "Ohm's Law for a section of a circuit"

Brief description of the document:

An 8th grade lesson on the topic “Ohm's Law for a Section of a Circuit” contains methodological development with computer support. Lesson objectives: to explore the dependence of the current flowing through a conductor on the voltage in a given section of the circuit and the resistance of the conductor, creating conditions for the development of experimental skills and abilities, the ability to substantiate one’s statements, the development of creative thinking, the ability to transfer acquired knowledge to a new situation, the formation of a scientific worldview through cognition of physical phenomena, formation of independent work skills. The lesson is based on the principle: observations => hypothesis => experiment => conclusion. When solving a problem, children derive Ohm's law for a section of a circuit. At the end of the lesson there is a test and qualitative tasks.

Relevance of the course . In the current state educational standard of basic general education, much attention is paid to the experimental training of students: developing their skills to describe and explain physical phenomena; use physical instruments and measuring instruments to experimentally determine physical quantities; present measurement results using tables, graphs and identify empirical dependencies on this basis, analyze the results and draw conclusions.

The current educational standard of basic general education makes the following requirements for the level of training of graduates of basic school in physics: be able to describe and explain physical phenomena; use physical instruments and measuring instruments to experimentally determine physical quantities; present measurement results using tables, graphs and identify empirical dependencies on this basis, etc.

Lesson Analysis

The object of training is the process of teaching physics to primary school students

The subject of training is the formation of students’ self-development competencies in the process of performing experimental tasks.

The purpose of the training is the scientific substantiation and development of methods for teaching physics, based on the use of experimental tasks as a means of developing students’ self-development competence.

Our teaching method was based on the following hypothesis : if we clarify the structure and content of self-development competencies, use a methodology based on the implementation of experimental tasks and use qualimetric analysis for objective assessment and correction, this will allow us to form students’ self-development competencies.

In accordance with the goal and hypothesis, the following tasks :

1. Based on the analysis of psychological, pedagogical and scientific-methodological literature, identify self-development competencies that are advisable to develop in schoolchildren in the process of teaching physics, and their main structural components.
2. To determine the role of experimental tasks in the process of forming self-development competencies of schoolchildren when teaching physics.
3. To develop a methodology for assessing the level of development of self-development competencies in schoolchildren when solving experimental problems.
4. To carry out an experimental test to assess the level of development of self-development competencies among schoolchildren.

In the process of realizing the set goal and solving problems, general scientific and special methods of theoretical and empirical research were used: analysis and synthesis of the basic principles of modern pedagogy, modeling of the patterns of the educational process; group processing of diagnostic procedure results; identification of quantitative indicators of the state of the educational environment.

Reflection on educational activities.

Let's summarize the lesson. We collect lesson cards in which the children noted the results of their work in the lesson.

The teacher suggests continuing the sentence:

• I found out…..
• I learned….
• Now I can….
• I like it

8th grade student Farrakhova Y.: I learned the dependence of current on voltage.

8th grade student Sabirov T.: I learned to experimentally determine the dependence of current on voltage.

8th grade student Besonnova S.: Now I can assemble simple electrical circuits.

8th grade student Metarshoev M.: I liked working with diagrams.

Lesson summary "OHM'S LAW FOR A CIRCUIT SECTION"

Lesson objectives: to explore the dependence of the current flowing through a conductor on the voltage in a given section of the circuit and the resistance of the conductor.

Tasks:

Forms of student work : individual, frontal, group work.

Results of student learning activities:

• understand that the current strength is directly proportional to the voltage at the ends of the conductor, if the resistance of the conductor does not change;
• understand that the current strength in a section of the circuit is inversely proportional to its resistance, if the voltage remains constant;
• know Ohm's law for a section of a circuit;
• be able to observe, compare, compare and generalize the results of a demonstration experiment;
• be able to apply Ohm's law to a section of a circuit when solving problems.

Key ideas:

• To teach to see the manifestations of the studied patterns in the surrounding life, to teach students to apply knowledge in a new situation, to develop the ability to explain surrounding phenomena, to improve skills in solving qualitative problems, to broaden the horizons of students.
• Develop the ability to work in a team in combination with independent work, develop communication skills.
• In the process of working with students, the teacher must take into account not only the individual needs of the student, but also general approaches to learning, while adapting to the needs of each individual.
• Using critical thinking technology techniques and new approaches to teaching to enhance students' cognitive activity.

Equipment: Presentation for the lesson, computer, screen, video projector; ammeter and voltmeter, V-24 current source, key, connecting wires.

Lesson structure:

I. Organizing time:

• -greetings;
• - identification of absentees;
• - checking the degree of readiness of students for the lesson;

II. Main part:

• Updating basic knowledge (performing creative tasks)
• Executing a test task
• A minute of rest "Perception"
• Carrying out a practical research task in groups
• Derivation of Ohm's law for a section of a circuit.
• Consolidation of knowledge, skills and abilities. (solving oral problems)

III. The final stage:

• Homework.
• Summing up the lesson, evaluating students' work.
• Reflection

During the classes.

1) Updating basic knowledge -10 min.

Hello guys, our lesson, I want to start with this quatrain:

How would our planet live?

How would people live on it?

Without heat, magnet, light

And electric rays.

Guys, knowledge of science always helps a person in life, but ignorance sometimes leads to tragic consequences. Draw the right conclusions for yourself from these words.

My quatrain mentions electric rays. What do you think it is? (electricity)

Questions:

1. What is electric current called?

Standard answer. Ordered directed movement of particles.

1. What is necessary for an electric current to exist in a circuit?

E.answer. The current source, conductors, current consumer, and all these elements must be closed.

3) Working with diagrams.

Now let’s check how you see irregularities in the design of electrical circuits.

In front of you are two emails. circuits, the diagrams of which are presented on the screen.

1. Why does the working lamp in the first circuit not light up when the key is closed? (Fig. 1)

Student response.

Standard answer. The electrical circuit has a break. In order for the lamp to light up, there must be an electric current in the circuit, and this is possible in a closed circuit consisting only of electrical conductors.

Teacher. How are conductors different from non-conductors or insulators?

Student response.

Standard answer. Conductors are bodies through which electrical charges can pass from a charged body to an uncharged one. But in insulators such transitions are impossible, and the lamp lights up.

The student who gave the correct answer is invited and, having eliminated the gap, demonstrates the correct answer. The lamp lights up.

2. Why doesn’t the bell ring in the second circuit when the circuit is closed? (Fig. 2)

Student response.

Standard answer. To produce electric current in a conductor, an electric field must be created in it. Under the influence of this field, free charged particles will begin to move in an orderly manner, and this is an electric current. An electric field in conductors is created and can be maintained for a long time by electric field sources. The electrical circuit must have a current source. We connect the circuit to a current source and the bell rings.

Performing a test of your choice: (see Test appendix)

After students complete the test in their notebooks, they enter a grade according to the scale on the evaluation sheet in the “Test completion” column.

A MINUTE OF REST

Guys, the great thinker Socrates was once asked what, in his opinion, is easiest in life? He replied that the easiest thing is to teach others, but the hardest thing is to know yourself.

In physics lessons we talk about understanding nature. But today let's take a look inside ourselves. How do we perceive the world around us? As artists or as thinkers?

1. Stand up, raise your arms up, stretch.
2. Interlace your fingers.
3. Look which finger of your left or right hand is at the top? Write down the result “L” or “P”
4. Cross your arms over your chest. (“Napoleon pose”) Which hand is on top?
5. Give a round of applause. Which hand is on top?

LET'S SUM UP

Considering that the result “LLL” corresponds to the artistic type of personality, and “PPP” corresponds to the type of thinking.

What type of thinking prevails in your class?

There are several “artists”, several “thinkers”, and most of the guys are harmoniously developed individuals who are characterized by both logical and imaginative thinking.

Learning new material

Before you are portraits of three physicists. One of them is closed. Based on the other two, you must guess whose portrait this is. It is about him, about his work, that we will talk about in today’s lesson. But there is a slight inaccuracy in this riddle.

Find it.(Ohms = Volts: Amps.)

I open Om's portrait. It is he who will reveal to us the secret into the world of electrical phenomena. So, guys, the topic of today’s lesson is “Ohm’s Law for a section of a circuit.” You probably noticed that the portraits of scientists correspond to units of measurement of physical quantities: current, voltage, resistance. So we must find out with you how these quantities are related to each other, what practical significance Ohm’s law has . But first, let's find out how Om discovered his law?

To consider the relationship between current, voltage and resistance, you need to turn to experience. Remember, to establish the dependence of one quantity on another, all others must be constant. First, let's look at how current depends on resistance. In front of you is an electrical circuit that includes devices (I show them the device, and they tell me what it is). The voltage at the ends of the conductor is always maintained constant. To do this, monitor the voltmeter reading. (I demonstrate experience and record instrument readings in a table). Guys, pay attention to the values ​​​​of the quantities shown in the table.

STUDENTS WORK IN GROUPS (students are divided into groups by the color of the cards)

Finding a solution to a problem (discovering new knowledge)

To do this, we will create four groups that will conduct research and then tell us about the results obtained. Remember the safety rules when assembling an electrical circuit

Work in groups ( each group gets a task )

The discussion of the results . (Representatives of the groups tell what they did and what results they got;)

-Name what elements the electrical circuits consisted of? Why are they needed? (current source - to create and maintain an electric field in the circuit, ammeter - to measure the current in the conductor, voltmeter - to measure the voltage at the ends of the conductor, resistor - provides the specified electrical resistance of the circuit, key - to close and open the circuit)

— We compare the conclusions obtained from groups No. 1 and No. 3; No. 2 and No. 4. The values ​​were different, but the conclusions were the same.

Conclusions:

1. With a constant resistance of a section of the circuit, the current strength in the conductor is directly proportional to the voltage at the ends of the conductor, i.e. The current increases as much as the voltage
2. At a constant voltage at the ends of the conductor, the current strength in the conductor is inversely proportional to the resistance, i.e. The current increases by the same amount as the resistance decreases.

We have with you R=const

U=const

— Obtain a formula expressing the relationship between three quantities.

(To replace the sign with , you need to put a proportionality coefficient, the value of which depends on the choice of units included in the formula. In the SI system k=1)

— The relationship between these three quantities is called “Ohm’s law for a section of a circuit,” because It was Georg Ohm in 1827 who was the first to experimentally establish the relationship between current, voltage and resistance.

— Formulate Ohm’s law for a section of the circuit. (The current strength in a section of the circuit is directly proportional to the voltage at the ends of this section and inversely proportional to its resistance)

Reflection on educational activities.

Let's summarize the lesson. We collect lesson cards in which the children noted the results of their work in the lesson.

The teacher suggests continuing the sentence:

• I found out…..
• I learned….
• Now I can….
• I like it…

The relationship of quantities in Ohm's law is embedded in the meaning of the poem that I composed for you:

Om Georg my name is I am a physicist without a doubt I have discovered a law, friends, of universal significance. If you want to know the voltage in the area, you must skillfully measure the strength of the current. If the current in it increases, then immediately, without a doubt, the voltage will go up, too, friends. Well, if the current strength begins to fall down, this means that the resistance has shown its whim. If the strength has become less, then the resistance will suddenly increase sharply. Remember this, friend.

Homework: fill out the cards in notebooks, read § 38,39 exercises 18,19

Establish the relationship between current strength, voltage in a homogeneous section of an electrical circuit and the resistance of this section.

Lesson objectives:

• Find out that the current in a section of a circuit is inversely proportional to its resistance, if the voltage remains constant
• Find out that the current strength is directly proportional to the voltage at the ends of the conductor, if the resistance does not change.
• Learn to apply Ohm's law to a section of a circuit when solving problems.
• Learn to determine current strength, voltage using a graph of the relationship between these quantities, as well as resistance.

Equipment:

screen, demonstration ammeter and voltmeter, current sources, key, connecting wires, demonstration resistance store, TCO, portraits of scientists.

Lesson plan:

1. Organizing time.
2. The purpose of preparation for the perception of new material.
3. Learning new material.
4. Consolidation of knowledge, skills and abilities.
5. Homework.
6. Summing up the lesson.

During the classes

1. Organizational moment.

Teacher:

According to the 19th century Russian poet Yakov Petrovich Polonsky,

The kingdom of science knows no limits - Everywhere there are traces of its eternal victories, Reason in word and deed, Power and light.

These words can rightfully be attributed to the topic that we are currently studying - electrical phenomena. They gave us many discoveries that illuminated our lives, literally and figuratively. And how much is still unidentified! What a field of activity for an inquisitive mind, skillful hands and inquisitive nature. So start your “perpetual motion machine” and go! Let us remember that while studying the topic “Electrical Phenomena,” you learned the basic quantities that characterize electrical circuits.

2. Updating students' knowledge.

Teacher:

At the beginning, please list the main quantities that characterize electrical circuits.
Students:
Current, voltage and resistance.
Teacher:
Now, give a short description of each of these quantities, according to the following plan:

1. Name of the Quantity.
2. What does this value characterize?
3. What is the formula?
4. In what units is it measured?
5. What device is used to measure or change?

Students:

1. Current strength

– characterizes the electric current in the conductor.

I = q / t – formula for finding the current strength, where q is the charge passing through the cross section of the conductor, t is the time the charge passes. The unit of measurement is ampere. The current is measured with an ammeter.

2. Voltage

– a quantity that characterizes the electric field.

U = A/q – formula for finding voltage, where A is the work of charge transfer through the cross section of the conductor, q-charge. The unit of measurement is volts. The voltage is measured with a voltmeter.

3. Resistance

: characterizes the conductor itself, denoted by R, unit of measurement is 1 Ohm.

Teacher:

Vovochka! Fill out the table on the board!

Correct, completed table.

Teacher:

Guys, what do you know about the scientists who discovered current strength, voltage, resistance?

(The students prepared reports about physicists.)

Students:

The units of measurement of the physical quantities current, voltage and resistance, are named after the scientists who discovered them. Ampere, Volt and Ohm.

1. Andre-Marie Ampère - on his monument there is an inscription: “He was as kind and as simple as he was great.” He was famous for his absent-mindedness. It was said about him that once, with a concentrated look, he boiled his watch in water for 3 minutes, holding an egg in his hand.

2. Alessandro Volta - was a knight of the Legion of Honor, received the rank of senator and count. Napoleon did not miss the opportunity to attend meetings of the French Academy of Sciences, where he spoke. Invented an electric battery, pompously called the “crown of vessels.”

3. Georg Simon Ohm - German physicist. He worked as a school teacher. He discovered the law of the dependence of current on voltage for a section of a circuit, as well as the law that determines the current in a closed circuit. He made a sensitive device for measuring current strength himself. Experiments and theoretical proofs were described by him in his main work, “Galvanic Circuit, Developed Mathematical,” published in 1827.

Multi-level tasks: (Tasks are completed by 2 groups of students).

Task No. 1.

1. How many amperes is 250mA?

A) 250A B) 25A C) 2.5A D) 0.25 A

2. Fill in the missing definition:

A value equal to ... is called electrical voltage. A) the product of power and current; B) the ratio of power to current; C) the ratio of work to the magnitude of the electric charge.

3. Draw a diagram of an electrical circuit: a current source, a switch, an ammeter, connecting wires, two light bulbs and a voltmeter that measures the voltage on one of the light bulbs.

Answer: (1 – G; 2 – V; 3 – ...)

Task No. 2.

1. How many kilovolts are in 750 V?

A) 750000 kV B) 0.75 kV C) 75 kV D) 7.5 kV

2. Fill in the missing definition:

A value equal to ... is called current strength. A) the ratio of work to the magnitude of the electric charge B) the ratio of the electric charge to time. C) doing work for time.

3. Draw a diagram of an electrical circuit: a current source, a switch, an ammeter, connecting wires, two light bulbs and a voltmeter that measures the voltage on the two light bulbs.

Answer: (1 – B; 2 –B; 3 –…)

3. Studying new material.

Teacher:

In previous lessons, guys, we studied current, voltage and resistance separately. Today we have set ourselves a goal: to reveal the interdependence of current, voltage and resistance in a section of an electrical circuit. Let's find out how the current depends on the resistance if the voltage remains constant.

Let's look at experience:

1.

Let's assemble a circuit consisting of: a current source, an ammeter, a voltmeter, conductors with a resistance of 1 Ohm, 2 Ohm, 4 Ohm.

2.

We alternately connect conductors with different resistances into the circuit. The voltage at the ends of the conductor is maintained constant during the experiment. We measure the current in the circuit with an ammeter.

We will place the measurement results in a table.

Teacher:

What did you observe?

Students:

As the resistance increases, the current decreases.

Teacher:

What conclusion can be drawn from this?

Students:

The current in a conductor is inversely proportional to the resistance of the conductor.

Teacher:

Let's find out how the current depends on the voltage if the resistance does not change.

Let's look at experience:

1.

Let's assemble a circuit consisting of a current source (galvanic cell), an ammeter, a spiral of nickel wire (conductor), a key and a voltmeter connected in parallel to the spiral.

2.

We connect the first element in series, the second, then the third of the same type, close the circuit and note the instrument readings each time an additional element is connected.

We will place the measurement results in a table.

Teacher:

What did you observe?

Students:

When the voltage doubles, the current doubles. With three elements, the voltage on the spiral increases threefold, and the current strength increases by the same amount.

Teacher:

What conclusion can be drawn from this?

Students:

The current strength in a conductor is directly proportional to the voltage at the ends of the conductor.

Teacher:

Using the results of experiments and the conclusions drawn from them, we will establish the relationship between current, voltage and resistance.

This notation is called Ohm's

for a section of the chain.

The current strength in a section of a circuit is directly proportional to the voltage at the ends of this section and inversely proportional to its resistance.

I = U/R

Historical information: This law was discovered by the German physicist Georg Simon Ohm in 1827.

Teacher:

To make it easier for you to remember the formula of Ohm's law, you can use the following way to write it.

Physical break.

Teacher:

Before we begin solving problems, let’s take a physical break. Let’s imagine that you and I are passengers on a bus... - the bus moves off sharply - the students must lean back, - the bus slows down - lean forward, - the bus turns to the right - lean to the left, - the bus turns to the left - lean to the right.

Teacher:

What physical phenomenon did you depict?

Students:

Inertia is the phenomenon of maintaining the speed of a body when no external forces act on this body.

4. Consolidation of skills and abilities.

Using Ohm's law for a section of the circuit, we will solve the problem.

Task 1.

The voltage at the terminals of the electric iron is 220V, the resistance of the heating element of the iron is 50 Ohms. What is the current in the heating element?

Given: U = 220V R = 50 Ohm I – ?

Solution: I = U/RI = 220V/50 Ohm = 4.4A Answer: 4.4A.

Task 2.

In Fig. shows a graph of current versus voltage for two conductors A and B. Determine the resistance of each conductor. Which of these conductors has the highest resistance?

Teacher:

We solve this problem by options. Option 1 – finds the resistance of conductor A. Option 2 – finds the resistance of conductor B.

Option 1.

Given: U = 6 V I = 3 A RA – ?

Solution: R = U/IR = 6 V/3 A = 2 Ohm Answer: 2 Ohm

Option 2.

Given: U = 4 V I = 1 A RB – ?

Solution: R = U/IR = 4 V/ 1 A = 4 Ohms Answer: 4 Ohms.

Students:

2 Ohm <4 Ohm, which means RA < RB, the resistance of conductor A is less than the resistance of conductor B.

5. Homework:

paragraphs 42 – 44, ex. 19 No. 3, 4.

6. Summing up the lesson, evaluating students’ work.

Self-diagnosis.