Outline of the lesson “Magnetic field of a coil with current. Electromagnets. Laboratory work “Assembling an electromagnet and testing its action. Assembling the electromagnet and testing its operation Assembling the electromagnet and testing its operation output

Plan - summary of a lesson in physics in grade 8 on the topic:

The magnetic field of a coil with current. Electromagnets.

Laboratory work No. 8 "Assembling an electromagnet and testing its operation."

Lesson Objectives: teach how to assemble an electromagnet from finished parts and experimentally check what its magnetic effect depends on.

Tasks.

Educational:

1. using the game form of activity in the lesson, repeat the basic concepts of the topic: magnetic field, its features, sources, graphic image.

2. organize activities in pairs of permanent and replaceable composition for the assembly of an electromagnet.

3. create organizational conditions for conducting an experiment to determine the dependence of the magnetic properties of a current-carrying conductor.

Developing:

1. develop students' skills of effective thinking: the ability to highlight the main thing in the material being studied, the ability to compare the facts and processes being studied, the ability to logically express their thoughts.

2. develop skills in working with physical equipment.

3. to develop the emotional-volitional sphere of students in solving problems of varying degrees of complexity.

Educational:

1. create conditions for the formation of such qualities as respect, independence and patience.

2. to promote the formation of a positive "I - competence".

Cognitive. Identify and formulate a cognitive goal. Build logical chains of reasoning.

Regulatory. They set a learning task based on the correlation of what has already been learned and what is still unknown.

Communicative. Share knowledge among group members to make effective joint decisions.

Lesson type: methodological lesson.

Problem-Based Learning Technology and CSR.

Equipment for laboratory work: collapsible electromagnet with parts (intended for frontal laboratory work on electricity and magnetism), current source, rheostat, key, connecting wires, compass.

Demos:

Structure and course of the lesson.

	Lesson stage	Stage tasks	Activity teachers	Activity student		Time
Motivational - indicative component
	Organizational stage	Psychological preparation for communication	Provides a favorable mood.	Getting ready for work.	Personal

	The stage of motivation and actualization (determining the topic of the lesson and the joint goal of the activity).	Provide activities to update knowledge and determine the objectives of the lesson.	Offers to play a game and repeat the basic concepts of the topic. Offers to discuss the positional task and name the topic of the lesson, determine the goal.	They are trying to answer, to solve a positional problem. Determine the theme of the lesson and the purpose.

Operational - executive component
	Learning new material.	To promote the activity of students in independent problem solving.	Offers to organize activities according to the proposed tasks.	Perform laboratory work. Work individually, in pairs. General work.	Personal, cognitive, regulatory
Reflective - evaluative component
	Control and self-examination of knowledge.	To identify the quality of assimilation of the material.	Offers to solve problems.	Decide. Answer. Discuss.	Personal, cognitive, regulatory
	Summing up, reflection.	An adequate self-assessment of the individual, his capabilities and abilities, advantages and limitations is formed.	Offers to answer the questions of the questionnaire "It's time to draw conclusions."	Answer.	Personal, cognitive, regulatory
	Submission of homework.	Consolidation of the studied material.	Writing on the board.	Recorded in a diary.	Personal

1. Repeat the basic concepts of the topic. Entrance testing.

Game "Continue the offer."

Substances that attract iron objects are called ... (magnets).

Interaction of a conductor with current and a magnetic needle
first discovered by a Danish scientist ... (Oersted).

Interaction forces arise between conductors with current, which are called ... (magnetic).

The places of the magnet, in which the magnetic effect is most pronounced, are called ... (magnet poles).

Around a conductor with electric current there is ...
(a magnetic field).

The source of the magnetic field is ... (a moving charge).

7. Lines along which the axes are located in a magnetic field
small magnetic arrows are called ... (magnetic lines of force).

The magnetic field around a conductor with current can be detected, for example, ... (using a magnetic needle or using iron filings).

9. Bodies that retain their magnetization for a long time are called ... (permanent magnets).

10. The same poles of the magnet ..., and the opposite - ... (repel,

are attracted

2. "Black box".

What is hidden in the box? You will find out if you understand what is at stake in the story from Dari's book "Electricity in its applications." Representation of a French magician in Algiers.

“On the stage is a small ironed box with a handle on the lid. I call a stronger person from the audience. In response to my challenge, an Arab of medium height, but strong build, came forward ...

- Approach the court, - I said, - and lift the box. The Arab bent down, picked up the box and arrogantly asked:

- Nothing else?

“Wait a little,” I replied.

Then, assuming a serious air, I made an imperious gesture and said in a solemn tone:

- You are now weaker than a woman. Try lifting the box again.

The strong man, not at all afraid of my charms, again took hold of the box, but this time the box resisted and, despite the desperate efforts of the Arab, remained motionless, as if chained to the place. The Arab tries to lift the box with enough force to lift a huge weight, but all in vain. Tired, out of breath and burning with shame, he finally stops. Now he's starting to believe in the power of sorcery."

(From the book of Ya.I. Perelman "Entertaining physics. Part 2".)

Question. What is the secret of sorcery?

Discuss. Express their position. From the "Black Box" I take out a coil, iron filings and a galvanic cell.

Demos:

1) the action of a solenoid (a coil without a core), through which a direct current flows, on a magnetic needle;

2) the action of the solenoid (coil with a core), through which a direct current flows, on the armature;

3) attraction of iron filings by a coil with a core.

They conclude what an electromagnet is and formulate the purpose and objectives of the lesson.

3. Performing laboratory work.

A coil with an iron core inside is called electromagnet. An electromagnet is one of the main parts of many technical devices. I suggest you assemble an electromagnet and determine what its magnetic effect will depend on.

Lab #8

"Assembling an electromagnet and testing its operation"

The purpose of the work: to assemble an electromagnet from finished parts and to test by experience what its magnetic action depends on.

Instructions for work

Task number 1. Make an electrical circuit from a battery, a coil, a key, connecting everything in series. Close the circuit and use the compass to determine the magnetic poles of the coil. Move the compass along the axis of the coil to a distance at which the effect of the magnetic field of the coil on the compass needle is negligible. Insert the iron core into the coil and observe the action of the electromagnet on the needle. Make a conclusion.

Task number 2. Take two coils with an iron core, but with a different number of turns. Check the poles with a compass. Determine the effect of electromagnets on the arrow. Compare and draw a conclusion.

Task number 3. Insert the iron core into the coil and observe the effect of the electromagnet on the arrow. Use the rheostat to change the current in the circuit and observe the effect of the electromagnet on the arrow. Make a conclusion.

They work in static pairs.

1 row - task number 1; 2 row - task number 2; 3 row - task number 3. They exchange tasks.

1 row - task number 3; 2 row - task number 1; 3 row - task number 2.They exchange tasks.

1 row - task number 2; 2 row - task number 3; 3 row - task number 1.They exchange tasks.

Work in pairs of shifts.

At the end of the experiments,conclusions:

1. if an electric current passes through the coil, then the coil becomes a magnet;

2.The magnetic action of the coil can be strengthened or weakened:
by changing the number of turns of the coil;

3. changing the strength of the current passing through the coil;

4. Inserting an iron or steel core into the coil.

Sheet myself training, myself checks and myself estimates.

1. Entrance testing.Game "Continue the offer."

1.__________________________

2.__________________________

3.__________________________

4.__________________________

5.__________________________

6.__________________________

7.__________________________

8.__________________________

9.__________________________

10._________________________

2. Laboratory work No. 8 "Assembling an electromagnet and testing its operation"

The purpose of the work: to assemble _______________ from finished parts and to verify by experience what _____________ action depends on.

Devices and materials: a galvanic cell, a rheostat, a key, connecting wires, a compass, parts for assembling an electromagnet.

Progress.

Task number 1.

Task number 2.

Task number 3.

Statement	I completely agree	Partially agree	Partially disagree	Completely disagree
I have acquired a lot of new information on the topic of the lesson
I felt comfortable
The information received in the lesson will be useful to me in the future.
I received answers to all my questions on the topic of the lesson.
I will definitely share this information with my friends.

Measurement of voltage in various parts of the electrical circuit.

Determining the resistance of a conductor using an ammeter and a voltmeter.

Objective: learn how to measure the voltage and resistance of a circuit section.

Devices and materials: power supply, spiral resistors (2 pcs.), ammeter and voltmeter, rheostat, key, connecting wires.

Instructions for work:

Assemble a circuit consisting of a power source, a key, two spirals, a rheostat, an ammeter connected in series. The rheostat engine is located approximately in the middle.
Draw a diagram of the circuit you have assembled and show on it where the voltmeter is connected when measuring the voltage on each spiral and on two spirals together.
Measure the current in the circuit I, the voltages U 1, U 2 at the ends of each spiral and the voltage U 1.2 in the section of the circuit consisting of two spirals.
Measure the voltage at the rheostat U p. and on the poles of the current source U. Enter the data in the table (experiment No. 1):

experience number	№1	№2
Current I, A
Voltage U 1, V
Voltage U 2, V
Voltage U 1.2 V
Voltage U p. , AT
Voltage U, V
Resistance R 1, Ohm
Resistance R 2, Ohm
Resistance R 1.2, Ohm
Resistance R p. , Ohm

Using a rheostat, change the resistance of the circuit and repeat the measurements again, recording the results in a table (experiment No. 2).
Calculate the sum of the voltages U 1 +U 2 on both spirals and compare with the voltage U 1.2. Make a conclusion.
Calculate the sum of the voltages U 1.2 + U p. And compare with the voltage U. Make a conclusion.
From each individual measurement, calculate the resistances R 1 , R 2 , R 1.2 and R p. . Draw your own conclusions.

Lab #10

Checking the laws of parallel connection of resistors.

Objective: check the laws of parallel connection of resistors (for currents and resistances). Remember and write down these laws.

Devices and materials: power supply, spiral resistors (2 pcs.), ammeter and voltmeter, key, connecting wires.

Instructions for work:

Carefully consider what is indicated on the panel of the voltmeter and ammeter. Determine the limits of measurements, the price of divisions. Use the table to find the instrumental errors of these instruments. Write down the data in a notebook.
Assemble a circuit consisting of a power source, a key, an ammeter and two spirals connected in parallel.
Draw a diagram of the circuit you have assembled and show on it where the voltmeter is connected when measuring the voltage at the poles of the current source and on the two spirals together, as well as how to connect the ammeter to measure the current in each of the resistors.
After checking by the teacher, close the circuit.
Measure the current in the circuit I, the voltage U at the poles of the current source and the voltage U 1.2 in the section of the circuit consisting of two spirals.
Measure the currents I 1 and I 2 in each spiral. Enter the data in the table:

Calculate the resistances R 1 and R 2, as well as the conductivity γ 1 and γ 2, of each spiral, the resistance R and the conductivity γ 1.2 of the section of two parallel-connected spirals. (Conductivity is the reciprocal of resistance: γ=1/ R Ohm -1).
Calculate the sum of the currents I 1 + I 2 on both spirals and compare with the current strength I. Draw a conclusion.
Calculate the sum of the conductivities γ 1 + γ 2 and compare with the conductance γ. Make a conclusion.

Evaluate direct and indirect measurement errors.

Lab #11

Determination of the power and efficiency of the electric heater.

Devices and materials:

Clock, laboratory power supply, laboratory electric heater, ammeter, voltmeter, key, connecting wires, calorimeter, thermometer, scales, beaker, vessel with water.

Instructions for work:

Weigh the inner beaker of the calorimeter.
Pour 150-180 ml of water into the calorimeter and lower the coil of the electric heater into it. The water should completely cover the coil. Calculate the mass of water poured into the calorimeter.
Assemble an electrical circuit consisting of a power source, a key, an electric heater (located in the calorimeter) and an ammeter connected in series. Connect a voltmeter to measure voltage across the electric heater. Draw a schematic diagram of this circuit.
Measure the initial temperature of the water in the calorimeter.
After checking the circuit by the teacher, close it, noting the moment in time it was turned on.
Measure the current through the heater and the voltage at its terminals.
Calculate the power generated by the electric heater.
After 15 - 20 minutes after the start of heating (note this point in time), measure the water temperature in the calorimeter again. At the same time, it is impossible to touch the electric heater spiral with a thermometer. Turn off the circuit.
Calculate useful Q - the amount of heat received by water and the calorimeter.
Calculate Q total, - the amount of heat released by the electric heater for the measured period of time.
Calculate the efficiency of a laboratory electric heating installation.

Use the tabular data from the textbook "Physics. 8th grade." edited by A.V. Peryshkin.

Lab #12

Study of the magnetic field of a coil with current. Assembling the electromagnet and testing its operation.

C spruce work: 1. explore the magnetic field of the coil with current using a magnetic needle, determine the magnetic poles of this coil; 2. assemble an electromagnet from ready-made parts and test its magnetic effect by experience.

Devices and materials: laboratory power supply, rheostat, key, ampemeter, connecting wires, compass, parts for assembling an electromagnet, various metal objects (carnations, coins, buttons, etc.).

Instructions for work:

Make an electrical circuit from a power source, a coil, a rheostat and a key, connecting everything in series. Close the circuit and use the compass to determine the magnetic poles of the coil. Perform a schematic drawing of the experiment, indicating on it the electric and magnetic poles of the coil, and depicting the appearance of its magnetic lines.
Move the compass along the axis of the coil to a distance at which the effect of the magnetic field of the coil on the compass needle is negligible. Insert the steel core into the coil and observe the action of the electromagnet on the arrow. Make a conclusion.
Use the rheostat to change the current in the circuit and observe the effect of the electromagnet on the arrow. Make a conclusion.
Assemble the arcuate magnet from prefabricated parts. Connect the magnet coils in series so that opposite magnetic poles are obtained at their free ends. Check the poles with a compass. Use a compass to determine where the north and where is the south pole of the magnet.
Using the resulting electromagnet, determine which of the bodies proposed to you are attracted to it, and which are not. Write down the result in a notebook.
In the report, list the applications of electromagnets known to you.
Make a conclusion from the work done.

Lab #13

Determination of the refractive index of glass

Objective:

Determine the refractive index of a glass plate shaped like a trapezoid.

Devices and materials:

Trapezium-shaped glass plate with plane-parallel edges, 4 sewing pins, protractor, square, pencil, sheet of paper, foam lining.

Instructions for work:

Lay a sheet of paper on the foam pad.
Place a plane-parallel glass plate on a sheet of paper and trace its contours with a pencil.
Lift up the foam pad and, without moving the plate, stick pins 1 and 2 into the sheet of paper. In this case, you need to look at the pins through the glass and stick pin 2 so that pin 1 is not visible behind it.
Move pin 3 until it is in line with the imaginary images of pins 1 and 2 in the glass plate (see Fig. a)).
Draw a straight line through points 1 and 2. Draw a straight line through point 3 parallel to line 12 (Fig. b)). Connect the points O 1 and O 2 (Fig. c)).

6. Draw a perpendicular to the air-glass interface at point O 1. Specify the angle of incidence α and the angle of refraction γ

7. Measure the angle of incidence α and the angle of refraction γ using

Protractor. Write down the measurement data.

Use a calculator or Bradis tables to find sin a and sing . Determine the refractive index of glass n Art. relative to air, considering the absolute refractive index of air n woz.@ 1.

You can determine n Art. and in another way, using Fig. d). To do this, it is necessary to continue the perpendicular to the air-glass interface as far down as possible and mark an arbitrary point A on it. Then continue the incident and refracted rays with dashed lines.
Drop from point A the perpendiculars to these extensions - AB and AC.Ð AO 1 C = a , Ð AO 1 B = g . Triangles AO 1 B and AO 1 C are rectangular and have the same hypotenuse O 1 A.
sin a \u003d sin g \u003d n st. =
Thus, by measuring AC and AB, one can calculate the relative refractive index of glass.
Estimate the error of the measurements made.

Topic: Assembling the electromagnet and testing its operation.

Objective: assemble an electromagnet from ready-made parts and test its magnetic effect by experience.

Equipment:

current source (battery or accumulator);
rheostat;
key;
connecting wires;
compass;
parts for assembling an electromagnet.

Instructions for work

1. Make an electrical circuit from a current source, a coil, a rheostat and a key, connecting everything in series. Close the circuit and use the compass to determine the magnetic poles of the coil.

2. Move the compass along the axis of the coil to such a distance that the effect of the magnetic field of the coil on the compass needle is negligible. Insert the iron core into the coil and observe the action of the electromagnet on the needle. Make a conclusion.

3. Use the rheostat to change the current in the circuit and observe the effect of the electromagnet on the arrow. Make a conclusion.

4. Assemble the arc magnet from the prefabricated parts. Connect the coils of an electromagnet to each other in series so that opposite magnetic poles are obtained at their free ends. Check the poles with a compass. Use a compass to determine where the north and where is the south pole of the magnet.

Lab No. 8 _____________________

the date

Assembling the electromagnet and testing its operation.

Target: assemble an electromagnet from ready-made parts and test by experience what its magnetic effect depends on.

Equipment: power supply, rheostat, key, connecting wires, compass (magnetic needle), arcuate magnet, ammeter, ruler, parts for assembling an electromagnet (coil and core).

Safety regulations.Read the rules carefully and sign that you agree to follow them..

Carefully! Electricity! Make sure that the insulation of the conductors is not broken. When conducting experiments with magnetic fields, you should take off your watch and put away your mobile phone.

I have read the rules and agree to abide by them. ________________________

Student Signature

Progress.

Make up an electrical circuit from a power source, a coil, a rheostat, an ammeter and a key, connecting them in series. Draw a circuit assembly diagram.

Close the circuit and use the magnetic needle to determine the poles of the coil.

Measure the distance from the coil to the needle L 1 and current I 1 in the coil.

Record the measurement results in table 1.

Move the magnetic needle along the axis of the coil to such a distance L2,

on which the effect of the magnetic field of the coil on the magnetic needle is negligible. Measure this distance and current I 2 in a coil. Also record the measurement results in Table 1.

Table 1

Coil

without core

L 1 cm

I 1, A

L 2 cm

I 2, A

4. Insert the iron core into the coil and observe the action

Electromagnet on the arrow. measure distance L 3 from the coil to the arrow and

Current strength I 3 in a core coil. Record the measurement results in

Table 2.

Move the magnetic needle along the axis of the core coil to

Distance L 4 , on which the action of the magnetic field of the coil on the magnetic

Arrow slightly. Measure this distance and current I 4 in the coil.

Also record the measurement results in Table 2.

table 2

Coil

core

L 3 cm

I 3, A

L 4 cm

I 4, A

Compare the results obtained in paragraph 3 and paragraph 4. Do conclusion: ______________

____________________________________________________________________

Use a rheostat to change the current in the circuit and observe the effect

Electromagnet on the arrow. Do conclusion: _____________________________

____________________________________________________________________

Assemble the arcuate magnet from prefabricated parts. Electromagnet coils

connect together in series so that opposite magnetic poles are obtained at their free ends. Check the poles with a compass, determine where the north and where is the south pole of the electromagnet. Sketch the magnetic field of the electromagnet you received.

TEST QUESTIONS:

What is the similarity between a coil with current and a magnetic needle? __________ ________________________________________________________________________________________________________________________________

Why does the magnetic effect of a coil carrying current increase if an iron core is introduced into it? ___________________________________________ ________________________________________________________________________________________________________________________________________________________________________________________________________________

What is an electromagnet? For what purposes are electromagnets used (3-5 examples)? ________________________________________________________ ________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________ ________

Is it possible to connect the coils of a horseshoe electromagnet so that the ends of the coil have the same poles? ________________________
________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________

What pole will appear at the pointed end of an iron nail if the south pole of a magnet is brought near its head? Explain the phenomenon ___________ __________________________________________________________________________ ________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________

MOU "Kremyanovskaya secondary school"

Plan - a summary of a lesson in physics in grade 8 on the topic:

The magnetic field of a coil with current. Electromagnets and their applications.

Teacher: Savostikov S.V.

Plan - a summary of a lesson in physics in grade 8 on the topic:

The magnetic field of a coil with current. Electromagnets and their applications.

Lesson Objectives:

- educational: to study ways of amplifying and weakening the magnetic field of a coil with current; teach to determine the magnetic poles of a coil with current; consider the principle of operation of an electromagnet and its scope; teach how to assemble an electromagnet from
finished parts and experimentally check what its magnetic effect depends on;

Developing: develop the ability to generalize knowledge, apply
knowledge in specific situations; develop instrument skills
mi; develop cognitive interest in the subject;

Educational: education of perseverance, diligence, accuracy in the performance of practical work.

Lesson type: combined (using ICT).

Lesson equipment: computers, author's presentation "Electromagnets".

Equipment for laboratory work: collapsible electromagnet with parts (intended for frontal laboratory work on electricity and magnetism), current source, rheostat, key, connecting wires, compass.

Demos:

1) the action of a conductor through which a constant

current, on a magnetic needle;

2) the action of a solenoid (coil without a core), through which a direct current flows, on a magnetic needle;

the attraction of iron filings by a nail, on which
wound wire connected to a constant source
current.

movelesson

I. Organizing time.

Announcement of the topic of the lesson.

P. Updating of basic knowledge(6 min).

"Continue the offer"

Substances that attract iron objects are called... (magnets).

Interaction of a conductor with current and a magnetic needle
first discovered by a Danish scientist... (Oersted).

Between conductors with current, interaction forces arise, which are called ... (magnetic).

The places in a magnet where the magnetic effect is strongest are called... (magnet poles).

Around a conductor with electric current there is ...
(a magnetic field).

The source of the magnetic field is ...(moving charge).

7. Lines along which the axes are located in a magnetic field
small magnetic needles are called ...(force magethread lines).

The magnetic field around a current-carrying conductor can be detected, for example, ... (using a magnetic needle or withusing iron filings).

If the magnet is broken in half, then the first piece and the second
a piece of magnet have poles... (northern -Nand southern -S).

11. Bodies that retain their magnetization for a long time are called ... (permanent magnets).

12. The same poles of the magnet ..., and the opposite - ... (repelled, attracted).

III. Main part. Learning new material (20 min).

Slides #1-2

Frontal survey

Why to study the magnetic field can be used
iron filings? (In a magnetic field, the filings are magnetized and become magnetic needles)

What is a magnetic field line called? (Lines along which the axes of small magnetic arrows are located in a magnetic field)

Why introduce the concept of a magnetic field line? (With the help of magnetic lines it is convenient to depict magnetic fields graphically)

How to show by experience that the direction of the magnetic lines
related to the direction of the current? (When the direction of the current in the conductor changes, all magnetic needles turn 180 about )

Slide №Z

What do these drawings have in common? (see slide) and how do they differ?

Slide #4

Is it possible to make a magnet that only has a north pole? But only the south pole? (Can't doa magnet with one of its poles missing).

If you break a magnet into two parts, will those parts be magnets? (If you break a magnet into pieces, then all of itparts will be magnets).

What substances can be magnetized? (iron, cobalt,nickel, alloys of these elements).

Slide number 5

Fridge magnets have become so popular that they are collectible. So at the moment, the record for the number of collected magnets belongs to Louise Greenfarb (USA). At the moment, in the Guinness Book of Records, it has a record of 35,000 magnets.

Slide #6

- Can iron nail, steel screwdriver, aluminum wire, copper coil, steel bolt be magnetized? (Iron nail, steel bolt and steel screwdriver can be used onmagnetize, but the aluminum wire and copper coil onyou can’t magnetize, but if you run an electric current through them, thenthey will create a magnetic field.)

Explain the experience shown in the pictures (see slide).

Slide number 7

Electromagnet

Andre Marie Ampere, conducting experiments with a coil (solenoid), showed the equivalence of its magnetic field to the field of a permanent magnet Solenoid(from the Greek solen - tube and eidos - view) - a wire spiral through which an electric current is passed to create a magnetic field.

Studies of the magnetic field of the circular current led Ampère to the idea that permanent magnetism is explained by the existence of elementary circular currents flowing around the particles that make up the magnets.

Teacher: Magnetism is one of the manifestations of electricity. How to create a magnetic field inside a coil? Can this field be changed?

Slides #8-10

Teacher demonstrations:

the action of a conductor through which a constant current flows
current, on a magnetic needle;

the action of a solenoid (coil without a core), through which a direct current flows, on a magnetic needle;

the action of a solenoid (coil with a core), according to which
direct current flows to the magnetic needle;

the attraction of iron filings by a nail, on which a wire is wound, connected to a direct current source.

Teacher: The coil consists of a large number of turns of wire wound on a wooden frame. When there is current in the coil, the iron filings are attracted to its ends; when the current is turned off, they fall off.

We include a rheostat in the circuit containing the coil and with the help of it we will change the current strength in the coil. With an increase in the current strength, the effect of the magnetic field of the coil with current increases, with a decrease, it weakens.

The magnetic effect of a coil with current can be greatly increased without changing the number of its turns and the current strength in it. To do this, you need to insert an iron rod (core) inside the coil. Iron, | led inside the coil, enhances its magnetic effect.

A coil with an iron core inside is called electromagnet. An electromagnet is one of the main parts of many technical devices.

At the end of the experiments, conclusions are drawn:

If an electric current flows through the coil, then the coil
becomes a magnet;

the magnetic action of the coil can be strengthened or weakened:
by changing the number of turns of the coil;

changing the strength of the current passing through the coil;

inserting an iron or steel core into the coil.

Slide #11

Teacher: The windings of electromagnets are made of insulated aluminum or copper wire, although there are also superconducting electromagnets. Magnetic cores are made from soft magnetic materials - usually from electrical or high-quality structural steel, cast steel and cast iron, iron-nickel and iron-cobalt alloys.

An electromagnet is a device whose magnetic field is created only when an electric current flows.

Slide #12

Think and answer

Can a wire wrapped around a nail be called an electromagnet? (Yes.)

What determines the magnetic properties of an electromagnet? (From
current strength, on the number of turns, on magnetic properties core, on the shape and dimensions of the coil.)

3. A current was let through the electromagnet, and then it was reduced to
twice. How did the magnetic properties of an electromagnet change? (Decreased by 2 times.)

Slides #13-15

1ststudent: William Sturgeon (1783-1850) - English electrical engineer, created the first horseshoe-shaped electromagnet capable of holding a load greater than its own weight (a 200-gram electromagnet was capable of holding 4 kg of iron).

The electromagnet, demonstrated by Sturgeon on May 23, 1825, looked like a bent into a horseshoe, varnished, iron rod 30 cm long and 1.3 cm in diameter, covered on top with a single layer of insulated copper wire. The electromagnet held a weight of 3600 g and was significantly stronger than natural magnets of the same mass.

Joule, experimenting with the very first rod magnet, managed to bring its lifting force up to 20 kg. This was also in 1825.

Joseph Henry (1797-1878), American physicist, perfected the electromagnet.

In 1827, J. Henry began to insulate not the core, but the wire itself. Only then did it become possible to wind the coils in several layers. J. Henry explored various methods of winding wire to obtain an electromagnet. He created a magnet of 29 kg, holding a gigantic weight at that time - 936 kg.

Slides #16-18

2ndstudent: The factories use electromagnetic cranes that can carry huge loads without fasteners. How do they do it?

An arcuate electromagnet holds an anchor (an iron plate) with a suspended load. Rectangular electromagnets are designed to capture and hold sheets, rails and other long loads during transportation.

As long as there is current in the electromagnet winding, not a single piece of iron will fall. But if the current in the winding is interrupted for some reason, an accident is inevitable. And such cases happened.

In one American factory, an electromagnet lifted iron ingots.

Suddenly, at the Niagara Falls power plant, which supplies current, something happened, the current in the electromagnet winding disappeared; a mass of metal fell off the electromagnet and fell with all its weight on the head of the worker.

In order to avoid the recurrence of such accidents, and also in order to save the consumption of electrical energy, special devices began to be arranged with electromagnets: after the objects being transported were lifted by a magnet, strong steel grabs were lowered and tightly closed on the side, which then themselves supported the load, while the current during transportation is interrupted.

Electromagnetic traverses are used to move long loads.

In seaports, perhaps the most powerful round lifting electromagnets are used to reload scrap metal. Their weight reaches 10 tons, carrying capacity - up to 64 tons, and tear-off force - up to 128 tons.

Slides #19-22

3rd student: Basically, the field of application of electromagnets is electrical machines and devices included in industrial automation systems, in the protection equipment of electrical installations. Useful properties of electromagnets:

quickly demagnetized when the current is turned off,

it is possible to manufacture electromagnets of any size,

during operation, you can adjust the magnetic action by changing the current strength in the circuit.

Electromagnets are used in lifting devices, for cleaning coal from metal, for sorting different varieties of seeds, for molding iron parts, and in tape recorders.

Electromagnets are widely used in engineering due to their remarkable properties.

Single-phase alternating current electromagnets are designed for remote control of actuators for various industrial and household purposes. Electromagnets with a large lifting force are used in factories to carry steel or cast iron products, as well as steel and cast iron shavings, ingots.

Electromagnets are used in telegraph, telephone, electric bell, electric motor, transformer, electromagnetic relay and many other devices.

As part of various mechanisms, electromagnets are used as a drive to carry out the necessary translational movement (turn) of the working bodies of machines or to create a holding force. These are electromagnets for lifting machines, electromagnets for clutches and brakes, electromagnets used in various starters, contactors, switches, electrical measuring instruments, and so on.

Slide #23

4th student: Brian Thwaites, CEO of Walker Magnetics, is proud to present the world's largest suspended electromagnet. Its weight (88 tons) is about 22 tons more than the current winner of the Guinness Book of Records from the USA. Its carrying capacity is approximately 270 tons.

The world's largest electromagnet is used in Switzerland. The octagonal electromagnet consists of a core made of 6400 tons of low carbon steel and an aluminum coil weighing 1100 tons. The coil consists of 168 turns, fixed by electric welding on the frame. A current of 30 thousand A, passing through the coil, creates a magnetic field with a power of 5 kilogauss. The dimensions of the electromagnet, which exceed the height of a 4-storey building, are 12x12x12 m, and the total weight is 7810 tons. It took more metal to make it than to build the Eiffel Tower.

The heaviest magnet in the world has a diameter of 60 m and weighs 36 thousand tons. It was made for a 10 TeV synchrophasotron installed at the Joint Institute for Nuclear Research in Dubna, Moscow region.

Demonstration: Electromagnetic telegraph.

Fixing (4 min).

3 people on computers do the work "Reshalkin" on the topic "Electromagnet" from the site
Slide #24

What is an electromagnet? (Iron core coil)

What are the ways to increase the magnetic effect of the coil with

current? (the magnetic effect of the coil can be enhanced:
by changing the number of turns of the coil, by changing the current flowing through the coil, inserting an iron or steel core into the coil.)

In which direction is the current coil installed?
suspended on long thin conductors? what a resemblance
does it have a magnetic needle?

4. For what purposes are electromagnets used in factories?

Practical part (12 min).

Slide #25

Laboratory work.

Self-fulfillment by students of laboratory work No. 8 "Assembling an electromagnet and testing its operation, p.175 of the Physics-8 textbook (author A3. Peryshkin, Bustard, 2009).

Sla ides No. 25-26

Summarizing and grading.

VI. Homework.

2. Complete a home research project "Motor for
minutes" (instruction is given to each student for work
at home, see Appendix).

Project "Motor in 10 minutes"

It is always interesting to observe changing phenomena, especially if you yourself participate in the creation of these phenomena. Now we will assemble the simplest (but really working) electric motor, consisting of a power source, a magnet and a small coil of wire, which we will also make ourselves. There is a secret that will make this set of items become an electric motor; a secret that is both clever and amazingly simple. Here's what we need:

1.5 V battery or rechargeable battery;

holder with contacts for the battery;

1 meter of wire with enamel insulation (diameter 0.8-1 mm);

0.3 meters of bare wire (diameter 0.8-1 mm).

We'll start by winding the coil, the part of the motor that will spin. To make the coil sufficiently even and round, we wind it on a suitable cylindrical frame, for example, on an AA battery.

Leaving 5 cm of wire free at each end, we wind 15-20 turns on a cylindrical frame. Don't try to wind the spool too tightly and evenly, a small degree of freedom will help the spool retain its shape better.

Now carefully remove the coil from the frame, trying to maintain the resulting shape.

Then wrap the free ends of the wire several times around the turns to keep the shape, making sure that the new binding turns are exactly opposite each other.

The coil should look like this:

Now it's time for the secret, the feature that will make the motor work. This is a subtle and non-obvious technique, and it is very difficult to detect when the motor is running. Even people who know a lot about how engines work may be surprised to discover this secret.

Holding the spool upright, place one of the free ends of the spool on the edge of a table. With a sharp knife, remove the top half of the insulation from one free end of the coil (holder), leaving the bottom half intact. Do the same with the other end of the coil, making sure that the bare ends of the wire are pointing up at the two free ends of the coil.

What is the meaning of this approach? The coil will lie on two holders made of bare wire. These holders will be attached to different ends of the battery so that electrical current can flow from one holder through the coil to the other holder. But this will only happen when the bare halves of the wire are lowered down, touching the holders.

Now you need to make support for the coil. it
just coils of wire that support the coil and allow it to spin. They are made of bare wire, so
how, in addition to supporting the coil, they must deliver an electric current to it. Just wrap each piece of uninsulated pro
water around a small nail - get the right part of our
engine.

The base of our first motor will be the battery holder. It will also be a suitable base because, with the battery installed, it will be heavy enough to keep the motor from shaking. Assemble the five pieces together as shown in the picture (without the magnet at first). Put a magnet on top of the battery and gently push the coil...

If done correctly, the reel will start spinning fast!

I hope that everything will work for you the first time. If, nevertheless, the motor does not work, carefully check all electrical connections. Does the coil rotate freely? Is the magnet close enough? If not enough, install additional magnets or trim the wire holders.

When the motor starts, the only thing you need to pay attention to is that the battery does not overheat, since the current is large enough. Just remove the coil and the circuit will be broken.

Show your motor model to your classmates and teacher at the next physics lesson. Let the comments of classmates and the teacher's assessment of your project become an incentive for further successful design of physical devices and knowledge of the world around you. Wish you success!

Lab #8

"Assembling an electromagnet and testing its operation"

Objective: assemble an electromagnet from ready-made parts and test by experience what its magnetic effect depends on.

Devices and materials: a battery of three elements (or accumulators), a rheostat, a key, connecting wires, a compass, parts for assembling an electromagnet.

Instructions for work

1. Make an electrical circuit from a battery, a coil, a rheostat and a key, connecting everything in series. Close the circuit and use the compass to determine the magnetic poles of the coil.

Move the compass along the axis of the coil to a distance at which the effect of the magnetic field of the coil on the compass needle is negligible. Insert the iron core into the coil and observe the action of the electromagnet on the needle. Make a conclusion.

Use the rheostat to change the current in the circuit and observe the effect of the electromagnet on the arrow. Make a conclusion.

Assemble the arcuate magnet from prefabricated parts. Connect the coils of an electromagnet in series with each other so that opposite magnetic poles are obtained at their free ends. Check the poles with a compass. Use a compass to determine where the north and where is the south pole of the magnet.

History of the electromagnetic telegraph

AT In the world, the electromagnetic telegraph was invented by the Russian scientist and diplomat Pavel Lvovich Schilling in 1832. Being on a business trip in China and other countries, he acutely felt the need for a high-speed means of communication. In the telegraph apparatus, he used the property of the magnetic needle to deviate in one direction or another, depending on the direction of the current passing through the wire.

Schilling's apparatus consisted of two parts: a transmitter and a receiver. Two telegraph apparatuses were connected by conductors to each other and to an electric battery. The transmitter had 16 keys. If you pressed the white keys, the current went in one direction, if you pressed the black keys, in the other. These current pulses reached the wires of the receiver, which had six coils; near each coil, two magnetic needles and a small disk were suspended on a thread (see left figure). One side of the disk was painted black, the other side white.

Depending on the direction of the current in the coils, the magnetic needles turned in one direction or another, and the telegraph operator receiving the signal saw black or white circles. If no current was supplied to the coil, then the disk was visible as an edge. Schilling developed an alphabet for his apparatus. Schilling's devices worked on the world's first telegraph line, built by the inventor in St. Petersburg in 1832, between the Winter Palace and the offices of some ministers.

In 1837, the American Samuel Morse designed a telegraph machine that records signals (see right figure). In 1844, the first telegraph line equipped with Morse devices was opened between Washington and Baltimore.

Morse's electromagnetic telegraph and the system he developed for recording signals in the form of dots and dashes were widely used. However, the Morse apparatus had serious shortcomings: the transmitted telegram had to be deciphered and then written down; low transmission speed.

P The world's first direct-printing machine was invented in 1850 by the Russian scientist Boris Semenovich Jacobi. This machine had a printing wheel that rotated at the same speed as the wheel of another machine installed at a neighboring station (see bottom figure). On the rims of both wheels were engraved letters, numbers and signs wetted with paint. Electromagnets were placed under the wheels of the vehicles, and paper tapes were stretched between the anchors of the electromagnets and the wheels.

For example, you need to send the letter "A". When the letter A was located at the bottom on both wheels, a key was pressed on one of the devices and the circuit was closed. The armatures of the electromagnets were attracted to the cores and pressed paper tapes to the wheels of both devices. The letter A was imprinted on the tapes at the same time. To transmit any other letter, you need to “catch” the moment when the desired letter is on the wheels of both devices below, and press the key.

What are the necessary conditions for correct transmission in the Jacobi apparatus? First, the wheels must rotate at the same speed; the second is that on the wheels of both devices, the same letters should occupy the same positions in space at any time. These principles were also used in the latest models of telegraph devices.

Many inventors worked on the improvement of telegraph communications. There were telegraph machines that transmitted and received tens of thousands of words per hour, but they were complex and cumbersome. At one time, teletypes were widely used - direct-printing telegraph devices with a keyboard like a typewriter. Currently, telegraph devices are not used; they have been replaced by telephone, cellular and Internet communications.

Explanatory note

... №6 on topic current Magnetic field. Magnetic field direct current. Magnetic lines. 1 55 Magnetic field coils With current. Electromagnets and them at...

Program in physics for grades 7-9 of educational institutions Program authors: E. M. Gutnik, A. V. Peryshkin M.: Bustard. 2007 textbooks (included in the Federal List)

Program

... №6 on topic"The work and power of the electric current» 1 Electromagnetic phenomena. (6 h) 54 Magnetic field. Magnetic field direct current. Magnetic lines. 1 55 Magnetic field coils With current. Electromagnets and them at...

Order No. of “ ” 201 Work program in physics for the basic level of studying physics at the basic school class 8

Working programm

... physics. Diagnostics on repeated material 7 class. Diagnostic work Section 1. ELECTROMAGNETIC PHENOMENA Topic ... magnetic fields coils With current from the number of turns, from strength current in reel, from the presence of a core; application electromagnets ...