Why is the dependence of voltage on current strength linear. Topic: Dependence of current on voltage

MBOU SOSH № 1 p. Izmalkovo, Izmalkovsky municipal district, Lipetsk region

Physics lesson in grade 8 on the topic:

According to the textbook

Peryshkina A.V. Physics. 8 cl.

Developer: Trubitsina M.A.

physics teacher MBOU secondary school № 1 p. Izmalkovo, Izmalkovsky municipal district

Lipetsk region.

Slide number 1

Lesson topic: Dependence of current strength on voltage. Electrical resistance.

Slide number 2

Lesson objectives:

Establish the relationship between voltage and current in the circuit;

Understand the concept of electrical resistance;

Establish a method for determining electrical resistance using an ammeter and a voltmeter;

Determine the unit of measurement for electrical resistance;

Find out the nature of email. resistance;

Establish the dependence of the resistance on the properties of the conductor.

Equipment

for a demo experience:

demonstration ammeter and voltmeter, key, connecting wires, instrument for electrolysis demonstration, rectifier.

for a frontal experience:

rheostats, ammeters, voltmeters, 1.2.4 ohm resistors, keys, connecting wires.

During the classes

1, Introduction.

In our life, we widely use the action of electric current. What e-mail actions do you know?

We can no longer imagine our existence without an electric current. Therefore, it is so important to know everything about this phenomenon. How does it arise? What does it depend on? What influences him?

You are already familiar with electrical voltage. And today you have to consider another phenomenon associated with the passage of email. current through the conductors.

2. Actualization of knowledge (repetition)

To do this, we need to briefly review the basic concepts associated with email. current.

Slide number 3

Please finish the phrase:

1. Electric current is ...

2. The current strength is ...

3. The current is measured ...

4. The ammeter is included in the circuit ... taking into account ... (show)

7. The voltmeter is included in the circuit ... taking into account ...

10. A rheostat is a device for ... (show)

3. Learning new material.

Great, you are ready for a new phenomenon affecting the current in a conductor.

Slide number 4

1. Collect email circuit according to the diagram displayed on the screen. Let's name its main elements and find them on our tables. The voltmeter is not accidentally highlighted in a different color. You will connect it to a resistor after assembly. Pay attention to the safety data sheet.
2. You are ready? Let's analyze the results of your experiments.

What is the nature of the relationship between U and I?

What is the coefficient of proportionality between U and I?

Slide number 5

Check your results against the picture on the slide. Did the current strength change in your experiments? And the aspect ratio? What was your equal? You had the same ammeters, voltmeters, rheostats, you put the rheostat lever in one position. What was different? When did the aspect ratio change? (another resistor). So whose property reflects the coefficient of proportionality? (resistor property). As soon as we increased the current in the section of the circuit where there was a resistor, the voltage immediately increased in this section. What characterizes stress? (work of the electric field) The greater the current in the section of the circuit, the great job have to be done when moving charges in this area. As if in the conductor (resistor), something counteracts the passage of e-mail. current. And this opposition was mathematically expressed in the proportionality coefficient between voltage and current. So what property of the conductor have we discovered today? (property to resist the passage of electric current). This property was called the electrical resistance of the conductor. Designate email resistance we will be the letter R.

Slide number 6 (a)

Now, maybe someone will immediately suggest a formula for calculating R?

After the answer -

Slide number 6 (b)

To use this formula, you must measure the current and voltage with a voltmeter and ammeter.

Let's summarize our experiment.

1. What is the connection on the section of the circuit between current and voltage?
2. What new property of conductors have we discovered?
3. How can you determine R?

Slide number 7

Using the last formula, you can immediately enter the unit of measurement for electrical resistance. This unit is called Om.

Slide number 8

4) Well, now we will try to establish the reasons for the occurrence of e-mail. resistance.

Slide number 9

Look at the screen. In front of you internal structure metal conductor, its crystal lattice. What particles are in the nodes of the crystal lattice? What particles move freely and randomly between the sites of the crystal lattice? What else is needed for e-mail to appear? current? Do you think electrons interact with atom-ions in their directed motion? How? Why?

And will the electrons interact with each other? How? Why?

Will these interactions affect the speed and direction of motion of the electrons? How?

Will this affect the magnitude of the current in the conductor? How?

So what is the reason for the conductor's opposition to the passage of e-mail. current?

Slide number 10 (we'll write it down)

5) It remains for us to find out what other characteristics of the conductor determine its email. resistance.

Let's do a little experiment. Let us now take a liquid conductor (electrolyte) as a conductor. What particles are current carriers in electrolytes? Will they interact with each other?

The interaction of ions with each other determines the resistance of the electrolyte. From experience we conclude:

R depends on the nature of the conductor

R increases with the length of the conductor

R increases with decreasing conductor cross-sectional area

Slide number 11

So what properties of a conductor affect its electrical resistance?

Slide number 12

6) Is the human body a conductor?

This means that the current passing through the body can affect the vital organs and even cause the death of a person.

Slide number 13

The severity of the defeat email. current depends on el. resistance of the human body, which is taken equal to 1000 ohms. but different parts of the human body have different resistance. Resistance is influenced by the person's condition, the presence of alcohol in the blood, perspiration, pollution, cuts, which lower the body's resistance to email. current. moreover, there are acupuncture points on the body ...

7) Summing up the lesson

Slide number 14

8) Open diaries, write down homework

9) Grades for the lesson

Slide number 15

10) Now let's think together

Slide number 16

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Slide captions:

Dependence of current strength on voltage. Electrical resistance. Lesson topic

Lesson objectives: to establish the relationship between voltage and current in the circuit; understand the concept of electrical resistance of a conductor; establish a method for determining resistance using an ammeter and a voltmeter; determine the unit of measurement for electrical resistance; find out the nature of electrical resistance; establish the dependence of resistance on the properties of the conductor.

Repetition: Electric current is ... The strength of the current characterizes ... The strength of the current is measured ... The ammeter is included in the circuit ... taking into account ... Voltage is ... The voltage is measured ... The voltmeter is included in the circuit ... taking into account ... The voltage is measured in ... The voltage in the network is 220 V. This means ... A rheostat is a device for ...

Task Assemble the electrical circuit according to the scheme: Moving the rheostat lever, each time take the readings of the ammeter and voltmeter and enter them into the table of results. (Take three measurements.) Plot the voltage versus current across the resistor. Determine the proportionality factor between current and voltage. Remember! Connect the power supply last. All changes in the circuit are made with an open key. You can start work only with the permission of the teacher. And V + + + - - -. ...

U, B I, A k = 4 k = 2 k = 1

Formula for calculating electrical resistance R = U / I R - electrical resistance of the conductor

Conclusion: on the section of the circuit U ~ I; conductors have electrical resistance; resistance can be determined using an ammeter and voltmeter according to the formula: R = U / I.

For a unit of resistance, 1 ohm is taken - the resistance of such a conductor in which, with a voltage at the ends of 1 V, the current strength is 1 A. Georg Ohm (1787-1854)

Causes of electrical resistance: + + + + + + + - - - - - - - - - - - - - - - - - - - - - - - - - -

The reason for the electrical resistance of a conductor is the interaction of conduction electrons with atom-ions of the crystal lattice and with each other.

The dependence of the electrical resistance R on the length of the conductor l and the cross-sectional area S. Than> l, the I Than

Influence of conductor properties on electrical resistance. R depends on the nature of the conductor. R ~ l (conductor length). R ~ 1 / S (conductor cross-sectional area).

The effect of electric current on a person. Current strength, mA Character of perception Alternating current(50 Hz) D.C 0.6-0.15 Onset of sensation, slight tingling and trembling of fingers. Not felt. 2-3 Violent trembling of fingers. Not felt 5-10 Feeling of pain, hand cramps. Itching, sensation of heating. 12-15 Hands are difficult to detach from the electrodes. Severe pain in fingers and hands. The condition is tolerable for 5-10 s. Increased heating. 20-25 Hands are immediately paralyzed, and it is impossible to tear them off the electrodes. Difficulty breathing. The condition is tolerable for no more than 5 s. An even greater increase in heating. Slight contraction of the arm muscles. 50-80 Respiratory paralysis. Violation of cardiac activity. Strong heating sensation. Contraction of the muscles of the arms. Convulsions. Difficulty breathing. 90-110 Respiratory paralysis. With a duration of 3 s or more, cardiac paralysis occurs. Death. Respiratory paralysis.

Lesson summary: Any conductor has electrical resistance. Electrical resistance is determined only by the properties of the conductor itself and does not depend on the strength of the current and voltage in the circuit. The severity of an electric shock to a person depends not only on the nature of the current, but also on the resistance of the human body, which can vary.

Homework: §§ 42 - 43, exercise. 17 (2), exercise. 18 (1.2)

Let's think together! The wire was stretched a little. Has her resistance changed and how? A piece of wire was bent in half and twisted. Has her resistance changed? How? How many times?

Topic: Dependence of current on voltage

Target: Establish the dependence of the current on the voltage.

Tasks:

Educational:

1. Review concepts from previous topics(current strength, electrical voltage, electricity, serial connection, parallel connection, ammeter, voltmeter).

2. To form a culture of communication among students through a crossword puzzle.

3. Fix new material by solving a qualitative quantitative problem to determine the voltage at the ends of the circuit section.

Developing:

1. To develop interest in the process of cognition through a demonstration experience with the help of instruments (ammeter, voltmeter).

2. Develop the attention of students through demonstration;

3. Develop thinking through problem solving.

Educational:

1. To cultivate the ability to work in a team with the help of a frontal survey, accuracy in drawing up a table. To study the new material "Dependence of current strength on voltage" by demonstration method to establish the dependence of current strength on voltage.

2. To cultivate the ability to work students in a group when checking homework.

Equipment:

Ammeter-1 piece, Voltmeter-1 piece, key-1 piece, rheostat-1 piece, power supply (rectifier) ​​-1 piece, connecting wires-6 pieces.

2. answer the questions on page 86;

3. complete exercise 19 on page 87;

Plan - lesson schedule

I . Organizing time. (2 minutes).

1. greeting (30 sec).

2. mark absent (1.30 min).

II. Writing homework in a diary. ( 1 minute ).

III. Homework check. ( 10 min ).

1. distribute cards, explain tasks - 1.30 min.

2. complete tasks - 8 min.

3. collect cards - 30 sec.

IV. Explanation of the new material. ( 17 minutes ).

1. Find out students' knowledge of past topics. (7 minutes)

A) Ammeter. Measurement of current strength.

B) Voltmeter. Voltage measurement.

B) Current strength.

D) Electric current.

E) Electrical voltage.

2.explanation new topic... (10 min).

Show experience confirming the dependence of the current on

voltage.

V... Anchoring. (8 minutes)

Anchor this topic with the solution of a quality problem.

Vi. Bottom line.(2 minutes).

1. Outcome of student activities. Statement of estimates. (2 minutes).

Plan - synopsis.

I. Organizing time. (2 minutes)

Hello children, sit down. Let's mark the absent ones.

II... Writing homework in diaries. (1 minute)

Open the diaries, write down your homework:

2. Answer the questions for paragraph 49 on page 86.

3. Complete exercise 19 on page 87.

close diaries, put aside.

III... Checking homework in diaries. (10 min)

Before embarking on a new topic, let's first check the homework in a non-standard way.

Divide into 3 groups (if there are a lot of students, then you can into 4).

Now listen carefully, now each group will receive a crossword puzzle and tokens (tokens should be according to the number of students in each group). You need to guess the words in the crossword puzzle as quickly as possible.

Everyone who guessed the word in the crossword puzzle takes one token for himself who has the most tokens, he pretends to good marks(distribute crosswords and tokens to students). You will have 8 minutes for all this.

Get a mark: "5" = more than 7; "4" = 4-6; "3" = 2-3. (the teacher distributes cards and gives the command for implementation).

IV... Explanation of the new material. (17 minutes)

1. Elucidate students' knowledge of past topics using a frontal survey (7 min)

Before moving on to the study of a new topic, we will repeat the previous topics.

Question : Give definitions of electric current? (name a specific student).

Answer: Electric current is the ordered movement of charged particles.

Question : What are the conditions for the existence of an electric current?

Answer: 1.the existence of a free charge.

2. the existence of an electric field.

Question : Well done. What actions of electric current exist?

Answer: Thermal, chemical, magnetic.

Question : What is the formula for expressing the current strength?

Answer: J = q / t. where q is charge, t is time.

Question : Charge unit?

Answer: Pendant.

Question : Time unit?

Answer: Seconds.

Question : Okay. What device is used to measure current?

Answer: Ammeter.

Question : Right. How is the ammeter connected?

Answer: Consistently.

Question : What is the definition of electrical voltage?

Answer: E Electric voltage is a physical quantity that characterizes the electric field that creates a current.

Question : Electric voltage designation?

Answer: U.

Question : The unit of measure for electrical voltage?

Answer: Volt.

Question : Now we are looking closely at the board. What's on the chalkboard? (ask a specific student).

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Answer: Electrical diagram.

Question : What device is needed to establish the dependence of the current on the voltage at constant resistance(ask a specific student).

Answer: Voltmeter.

Question : Right. How is the voltmeter connected?

Answer: Parallel.

Question : (Call a specific student to the board). Draw a voltmeter on the diagram.

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0 "style =" border-collapse: collapse; border: none ">

Draw horizontal line, retreated from this line by two cells, drew another horizontal line once again retreated from this line by two cells and so drew a horizontal line 5 times and retreat two cells. They retreated from the edge by 4 cells and drew vertical line and so we draw 4 times. And now we are all carefully looking at the diagram. We need to establish the dependence of the current on the voltage. To do this, by changing the voltage, (i.e. increasing), we look at the ammeter readings. (our resistance does not change, the teacher himself counts the resistance readings according to the law Ohm and the resulting number is entered into the table).

Question: How many divisions does the ammeter show?

Answer: 0.6

Question : We enter the ammeter readings in the table. Now we increase the voltage 2 times. We look at the ammeter readings. How many divisions does it show?

Answer: 1.2

Question : We enter the ammeter readings in the table. Now we increase the voltage 3 times. We look at the ammeter readings. How many divisions does it show?

Answer: 2.4

Experience result:

With a constant resistance R = 3, we apply a voltage U = 2, while the current strength takes on the value I = 0.6. When the voltage doubles U = 4, the ammeter will show twice the current I = 1.2. With a threefold increase in voltage U = 6, the ammeter will show three times the force I = 2.4.

Experience analysis: And now, according to the readings of the table, we will draw a graph of the dependence of the current strength on the voltage. The horizontal axis is the voltage in volts, and the vertical axis is the current in amperes.

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Question : What does it mean directly proportional?

Answer: As the voltage increases, the current increases.

Question : And when the voltage decreases, how does the current change?

Answer: Decreases.

So, according to the readings of the graph, we found out that with increasing voltage, the current increases.

V... Anchoring.(8 min)

Now let's solve the problem.

Task1 : (Decide verbally) .

Determine the current strength according to the graph. With a voltage at the ends of the circuit section equal to 3V, 5V, 7V, how much will the current in the conductor be? (ask a specific student, look at the graph).

Specific students are given grades on the performance of cards.

Psychological attitude

I'm in class now

physics. And about everything

the rest I will not think now, I will think about it later.

Lesson epigraph

“I think

hence,

I exist."

Rene Descartes

Set correspondence 1st level

1. Incandescent light bulb

3.Rheostat (resistance)

4. Ammeter

5. Voltmeter

Choose the correct designation Level 2

1. Designation and unit of measurement of current strength.

2. Designation and unit of resistance measurement

3. Designation and unit of voltage measurement

4. Formula for calculating the current

5. Formula for calculating voltage

• What work will a current of 3A do in 10 minutes with a voltage in the circuit of 15 V?

Checking the 1st level

Checking level 2

Checking level 3

t = 10 min 600s

q = 3 * 600 = 1800 C

A = 15 * 1800 = 27000J

Answer: A = 27kJ

The purpose of the lesson:

investigate the dependence of the current

From stress

From resistance

The dependence of I on U R is established remains unchanged (R = 10 Ohm)

Make a conclusion

Addiction straight proportional

At R = const, I ~ U

Let us establish the dependence of I on R U remains unchanged U = 3V

Make a conclusion

Addiction back proportional

At U = const,

0 1 0 2 0 3 0 4 0 5 0 6 0

At R = const, I ~ U

At U = const,

Law Ohm for plot chains.

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

U

Do you know how, when working with the Ohm's law formula, it is easy to write a formula for any input quantity? Using a triangle

Question number 3

Between what quantities does Ohm's law establish the relationship?

Question number 4

How does the current strength depend on the voltage?

• How does current strength depend on resistance?

Question number 6

• How is it formulated

Ohm's law?

• Lesson grade

• 18 - 16 - "5"
• 15 - 11 - "4"
• 10 - 8 - "3"

Learn Ohm's Law.

By technical data sheet any electrical appliance which you have to determine the resistance.

Various actions of current, such as heating a conductor, magnetic and chemical actions, depend on the strength of the current. By changing the current in the circuit, you can regulate these actions. But in order to control the current in the circuit, you need to know what the current strength in it depends on.

We know that electric current in a circuit is the ordered movement of charged particles in an electric field. The stronger the action of the electric field on these particles, the more obviously the current in the circuit.

But the action of the field is characterized by a physical quantity - voltage (§ 39). Therefore, we can assume that current strength depends on voltage... Let's establish this dependence on experience.

Figure 68, a shows an electrical circuit consisting of a current source, an ammeter, a spiral of nickel wire (conductor), a key and a voltmeter connected in parallel to the spiral. Figure 68, b shows a diagram of this circuit (a conductor is conventionally designated a rectangle).

Rice. 68. Installation for determining the dependence of the current on the voltage

Close the circuit and note the readings of the instruments. Then the second same power source is connected to the first source and the circuit is closed again. In this case, the voltage on the spiral will double, and the ammeter will show twice the current strength. At three sources the voltage on the spiral increases threefold, the current strength increases by the same amount.

Thus, experience shows that how many times the voltage applied to the same conductor increases, the current strength in it increases by the same amount. In other words, the current in the conductor is directly proportional to the voltage at the ends of the conductor.

Figure 69 shows a graph of the dependence of the current in a conductor on the voltage between the ends of this conductor.

Rice. 69. The graph of the dependence of the current in the conductor on the voltage

On the graph, in a conventionally selected scale, the horizontal axis shows the voltage in volts, and the vertical axis shows the current strength in amperes.

Questions

1. How to experimentally show the dependence of the current on the voltage?
2. How does the current strength in a conductor depend on the voltage at the ends of the conductor?
3. What is the graph of the dependence of current strength on voltage? What relationship between quantities does it reflect?

Exercise # 27

1. With a voltage at the ends of the circuit section equal to 2 V, the current in the conductor is 0.4 A. What should be the voltage so that the current in the same conductor is 0.8 A?
2. When the voltage at the ends of the conductor is 2 V, the current in the conductor is 0.5 A. What will be the current in the conductor if the voltage at its ends increases to 4 V; if the voltage at its ends decreases to 1 V?

Lesson topic: Dependence of current strength on voltage. Ohm's law for a section of a chain.

The purpose of the lesson: Establish the relationship between the current strength, voltage in a homogeneous area electrical circuit and the resistance of this site.

Lesson Objectives:

• Find out that the current in the circuit section 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 for a section of a chain when solving problems.
• learn how to determine the current strength, voltage according to the graph of the relationship between these values, as well as resistance.

Equipment: Screen, demonstration ammeter and voltmeter, current source, key, connecting wires, demonstration resistance store, TCO, portraits of scientists.

Lesson plan

1. Organizing time.
2. the purpose of preparing 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 limit -
Everywhere there are traces of her eternal victories,
Reason word and deed,
Strength and light.

These words can rightfully be attributed to the topic that we are now studying - electrical phenomena. They gave us many discoveries that have illuminated our lives in a literal and figurative sense. And how much more unidentified around! What a field of activity for an inquiring mind, skillful hands and an inquisitive nature. So start your "perpetual motion machine" and go!
Recall 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 strength, voltage and resistance.

Teacher: Now, give a small description of each of these quantities, according to the following plan:

1. The name of the quantity.
2. What does this value characterize?
3. What is the formula for?
4. In what units is it measured?
5. By what device is it measured or changed?

Students:
Current strength- characterizes the electric current in the conductor.
- the formula for finding the current strength, where q is the charge passing through the cross section of the conductor, t is the time of passage of the charge. The unit of measurement is ampere. The current is measured - with an ammeter.
Voltage is the quantity that characterizes the electric field.
Is the formula for finding the voltage, where A is the work of transferring charge through the cross section of the conductor, q is the charge. The unit of measurement is volts. The voltage is measured with a voltmeter.
Resistance characterizes the conductor itself, denoted - R, unit of measurement 1 Ohm.

Teacher: fill in table 1 on the board:

Table 1

Correctly, completed table 1:

Table 1

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

(Students prepared reports about scientists physicists)

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

André-Marie Ampere - his monument bears the inscription: "He was just 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.

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 the meetings of the French Academy of Sciences, where he spoke. He invented an electric battery, magnificently called the "crown of vessels".

Georg Ohm - German physicist. Experiments and theoretical proofs were described by him in the main work "Galvanic circuit, developed mathematically", published in 1827.

Multilevel tasks:

Task number 1

1. How many amperes are in 250 mA?

A) 250 A;
B) 25 A;
B) 2.5 A;
D) 0.25 A.

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 amount of electric charge.

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

Answer:(1 - G; 2 - B; 3 - Fig. 1)

Task number 2

1. How many kilovolts are there in 750 V?

A) 750,000 kV;
B) 0.75 kV;
B) 75 kV;
D) 7.5 kV.

2. Insert the missing definition:

The value equal to ... is called the current strength.

A) the ratio of work to the amount of electric charge;
B) attitude electric charge at the time;
C) the production of work for a time.

3. Draw an electrical circuit diagram: a current source, a key, an ammeter, connecting wires, two bulbs and a voltmeter that measures the voltage across two bulbs.

Answer:(1 - B; 2 - B; 3 - Fig. 2)

3. Learning new material

Teacher: In previous lessons, guys, we studied current strength, voltage and resistance separately. Today we have set a goal for ourselves: to reveal the interdependence of current strength, voltage and resistance in the section of the electrical circuit. Let us find out how the current strength depends on the resistance if the voltage remains constant.
Let's turn to 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. In the circuit, in turn, we include conductors with different resistance. The voltage at the ends of the conductor was kept constant during the experiment. We measure the current in the circuit with an ammeter.

We place the measurement results in table 2:

table 2

Teacher: What have you observed?

Students: With increasing resistance, 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 us find out how the current strength depends on the voltage, if the resistance does not change. Let's turn to experience:

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

2. We connect the second one to the first battery, then the third one is the same, we close the circuit and note the readings of the instruments each time an additional battery is connected.

The measurement results are placed in Table 3:

Table 3

Teacher: What have you observed?

Students: When the voltage was doubled, the current doubled. With three batteries, the voltage across the coil tripled, and the current increased by the same amount.

Teacher: What conclusion can be drawn from this?

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

Teacher: Using the results of the experiments, and the conclusions drawn from them, we will establish the dependence of the current strength, voltage and resistance.

Such a record is called Ohm's law for a chain section.

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

Teacher:

History reference: This law was discovered by the German physicist Georg Ohm in 1827. French schoolchildren study this law under the name of Pouillet - a French physicist who established the same law, but 10 years later.
Teacher: In order to make it easier for you to remember the Ohm's law formula, you can use the following method of writing it down. (fig. 3)

; ; U = I * R

Physical pause

Teacher: Before we start solving problems, we will take a physical pause. Let's imagine that we are bus passengers ...

• the bus starts to move abruptly - students must lean back.
• the bus slows down - lean forward.
• the bus turns right - lean to the left.
• the bus turns left - lean to the right.

Teacher: Which physical phenomenon did you portray?

Students: Inertia is the phenomenon of the conservation of the speed of a body when external forces do not 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.

Objective 1.

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

Given: U = 4B I= 1A RB – ?

Solution: ; Answer: 4 ohms.

Students: 2 ohm< 4 Ом, значит RA < RB, the resistance of conductor A is less than the resistance of conductor B.

5. Homework: p. 42–44, exercise 19 No. 3.4

6. Summing up the results of the lesson, assessing the work of students

Teacher: Well done guys, they did a very good job, solved problems well, listened attentively and took an active part in the derivation of Ohm's law. How the lesson went for everyone, we will now see from the results of self-diagnosis.

Self-diagnosis(students pick up one of the three cards on their desk).

• Red card- satisfied with the lesson, the lesson is useful for me, I worked and received a well-deserved mark; I understood everything that was said.
• Yellow card- the lesson was interesting, I answered from the spot, managed to complete a number of tasks. I'm comfortable enough in the lesson.
• Green card- I received little benefit from the lesson, I did not really understand what in question, I was not ready for an answer in the lesson.