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Strength and direction of electric current presentation. Presentation on the topic "direction of electric current"

Electricity. Current strength

When charged particles move in a conductor, an electric charge is transferred from one place to another. However, if charged particles perform random thermal motion, such as free electrons in a metal, then charge transfer does not occur. An electric charge moves through the cross section of the conductor only if, along with random movement, electrons participate in ordered movement. In this case, we say that an electric current is established in the conductor.

An electric current is called an ordered (directed) movement of charged particles.
An electric current arises from the ordered movement of free electrons and ions. If you move a neutral body as a whole, then, despite the orderly movement of a huge number of electrons and atomic nuclei, an electric current does not arise. The total charge transferred through any section of the conductor will then be equal to zero, since charges of different signs move with the same average speed.

Electric current has a certain direction. The direction of movement of positively charged particles is taken as the direction of the current. If the current is formed by the movement of negatively charged particles, then the direction of the current is considered opposite direction particle motion. (Such a choice of the direction of the current is not very successful, since in most cases the current is the movement of electrons - negatively charged particles. The choice of the direction of the current was made at a time when nothing was known about free electrons in metals.

We do not directly see the motion of particles in a conductor. About availability electric current one has to judge by the actions or phenomena that accompany it. First, the conductor through which the current flows heats up. Secondly, the electric current can change the chemical composition of the conductor, for example, release its chemical constituents (copper from a solution of copper sulphate, etc.). Thirdly, the current has a force effect on neighboring currents and magnetized bodies. This action of current is called magnetic. So, the magnetic needle near the current-carrying conductor rotates. The magnetic effect of the current, in contrast to the chemical and thermal ones, is the main one, since it manifests itself in all conductors without exception. The chemical effect of the current is observed only in solutions and melts of electrolytes, and heating is absent in superconductors.
Current action

If an electric current is established in the circuit, this means that through the cross section of the conductor all the time is transferred electric charge. The charge transferred per unit of time serves as the main quantitative characteristic of the current, called the current strength. If a charge ∆q is transferred through the cross section of the conductor during the time ∆t, then the current strength is equal to:
Current strength

Thus, the current strength is equal to the ratio of the charge ∆q transferred through the cross section of the conductor during the time interval ∆t to this time interval. If the current strength does not change with time, then the current is called constant. Current strength, like charge, is a scalar quantity. It can be both positive and negative. The sign of the current strength depends on which of the directions along the conductor is taken as positive. Current strength I > 0 if the direction of the current coincides with the conditionally chosen positive direction along the conductor. AT otherwise I

Ammeter. Current measurement

Prezentacii.com

establish empirically that the current strength is the same in all parts of the circuit

get acquainted with the new ammeter device
develop experimental skills (put forward and

substantiate a hypothesis, plan an experiment based on it
verification)

Targets and goals

What do we call electric current
Current sources
Current strength
What is the formula for current.
Current units
Remarkable Scientists

Electricity

Electricity- ordered (directed) motion of charged particles.

Conditions for the existence of current:

The presence of free charge carriers;

The presence of an electric field.

Current direction :

The direction of the ordered movement of positively charged particles is taken as the direction of the current. The direction of the current coincides with the direction of the strength of the electric field causing this current.

DC electric current

Direct electric current is a current whose strength does not change over time.

Direct current is widely used in automobile electrical circuits, as well as in microelectronics and so on.

A current source is a device that separates positive and negative charges.

accumulator, batteries, alternator...

Current sources

Current strength

Current in this moment time - a scalar physical quantity equal to the limit of the ratio of the electric charge that has passed through the cross section of the conductor to the time interval of its origin.

I - current strength, (A)

q - charge, (C)

t – time, (s)

I = q:t

Remarkable Scientists

Ampère André Marie. Years of life: 1775-1836. French physicist and mathematician. He created the first theory that expressed the connection between electrical and magnetic phenomena. Ampere owns a hypothesis about the nature of magnetism, he introduced the concept of "electric current" into physics.

Instrument for measuring current strength- Ammeter. The circuit is connected in series.

Formulate a goal;
To put forward and substantiate a hypothesis;
Make a plan for the experiment;
Select the necessary equipment;
To conduct an experiment;
Analyze results;
To conclude.

scientific experiment

Purpose: to determine the strength of the current in various parts of the circuit.

Hypothesis: do you think the ammeter readings in all parts of the circuit will be the same?

Determine the current flowing through the cross section of the lamp filament
Devices: battery, ammeter, conductor, wires, key, lamp.

Practical work

Group work.

Assembly of the electrical circuit of the following sequence:

1 group - battery, key, ammeter, lamp.

2 group - battery, ammeter, key, lamp.

3 group - battery, lamp, ammeter, key.

Study results table

№ groups

Prezentacii.com

The current strength in all parts of the circuit is the same when connected in series.

Primary fastening.
1. Determine by results practical work, what charge to pass through the cross section of the conductor in 2 minutes.
2. How many electrons pass in 2 minutes?

Independent work

1. Guys, what are the questions for me in the lesson?
2. What new did you learn at the lesson today?
3. What aroused your particular interest in the lesson?
4. Where do you find practical application of the acquired knowledge?
5. How do you evaluate your activity in the lesson

Reflection of activity.

38. UPR14(2); ex15(2); No. 1277 (L) - optional.
Additional material on the topic “The use of electrical measuring instruments in the basis of agricultural machinery.

Homework

Main questions 1. Electric current. Current strength. Direction of current 2. Resistance of conductors. Resistivity 3. Ohm's law for a circuit section direct current. Current-voltage characteristic of conductors. 4. Ways of connecting conductors 5. Current sources. Third party forces. EMF of the current source 6. Ohm's law for a closed circuit with a current source. 7. Work and current power 8. Measurement of current and voltage. Shunts and additional resistances

André Ampère () Introduced the concept of "electric current" into physics

An electric current is an ordered (directed) movement of charged particles. To obtain an electric current in a conductor, it is necessary to create an electric field in it. In order for an electric current to exist in a conductor for a long time, it is necessary to maintain an electric field in it all this time. This is done using current sources. The direction of movement of not free electrons, but positive charges, is taken as the direction of the electric current. Therefore, the electric current in the external circuit is directed from the positive to the negative pole of the current source.

For the emergence and maintenance of electric current, the following conditions are necessary: 1) the presence of free current carriers (free charges); 2) the presence of an electric field that creates an ordered movement of free charges; 3) free charges, in addition to the Coulomb forces, must be affected by external forces of a non-electric nature; these forces are created by various current sources ( galvanic cells, batteries, electric generators, etc.) 4) the electric current circuit must be closed.

Ampère André Marie. Years of life: French physicist and mathematician. He created the first theory that expressed the connection between electrical and magnetic phenomena. Ampere owns a hypothesis about the nature of magnetism, he introduced the concept of "electric current" into physics.

The unit of current strength is the current strength at which segments of parallel conductors 1 m long interact with a force of 2 * 10 -7 N (0, N) 1 AMP

When an electric circuit is closed, an electric current is generated. Free electrons under the influence of electric field forces move along the conductor. In their motion, the electrons collide with the atoms of the conductor and give them a reserve of their kinetic energy. The speed of movement of electrons is constantly changing: when electrons collide with atoms, molecules and other electrons, it decreases, then increases under the influence of an electric field and decreases again with a new collision. As a result, a uniform flow of electrons is established in the conductor at a speed of several fractions of a centimeter per second. Consequently, electrons passing through a conductor always encounter resistance from its side to their movement.

Substance Resistivity, Ohm * mm2 / m Silver 0.016 Copper 0.017 Gold 0.024 Aluminum 0.028 Iron 0.10 Tin 0.12 Constantan 0.5 Nichrome 1.1 The electrical resistance of the conductor depends on: 1) the length of the conductor, 2) the cross section of the conductor , 3) conductor material, 4) conductor temperature. The resistance of a conductor 1 m long, with a cross section of 1 mm 2 is called resistivity

Om Georg Years of life (). German physicist. He theoretically discovered and experimentally confirmed the law expressing the relationship between the current strength in the circuit, voltage and resistance.

I 1 R 2 I 1 R 2 25 I U 0 R1R1 R2R2 I1I1 I2I2 I 2 > I 1 R 2 I 1 R 2 I 1 R 2 I 1 R 2 I 1 R 2 title="(!LANG:I U 0 R1R1 R2R2 I1I1 I2I2 I 2 > I 1 R 2

Devices using which an electric field is created inside the conductors are called current sources. The current source consists of two conductors, a constant positive potential is maintained on one conductor, and a constant negative potential is maintained on the other. In an external circuit, positive electric charges move under the influence of Coulomb forces. To maintain a constant positive potential on the left conductor, the positive charges inside the current source must move against the Coulomb forces, this is possible only when they are acted upon by forces of non-electrical origin - external forces. External forces must be greater than the Coulomb forces and directed in the opposite direction.

External forces arise as a result of friction Until the end of the 18th century, all technical current sources were based on friction electrification. The most effective of these sources has become an electrophoretic machine (the disks of the machine are driven in opposite directions. As a result of the friction of the brushes on the disks, charges of the opposite sign accumulate on the conductors of the machine).

The first electric battery appeared in 1799. It was invented by the Italian physicist Alessandro Volta (), an Italian physicist, chemist and physiologist, the inventor of a constant electric current source. His first current source - "voltaic column" was built in strict accordance with his theory of "metallic" electricity. Volta put several dozen small zinc and silver circles on top of each other alternately, laying paper moistened with salted water between them.

The zinc atom donates two electrons, turns into a positive zinc ion and goes into solution. The electrons leave the zinc electrode through the wires, thereby removing a negative charge from it, which could prevent further dissolution of the electrode. The electrons fall on the copper electrode, where the copper ion comes up and, having received two electrons, settles already as a neutral atom on the copper electrode.

Third-party forces arise under the influence of light Solar battery When certain substances are illuminated with light, a current appears in them, light energy is converted into electrical energy. AT this instrument charges are separated by light. Solar panels are made up of photovoltaic cells. Applied in solar panels, light sensors, calculators, video cameras. Photocell

Third-party forces arise under the action of heat Thermocouple Thermoelement (thermocouple) - two wires from different metals must be soldered from one edge, then the junction is heated, then a current appears in them. The charges are separated when the junction is heated. Thermoelements are used in thermal sensors and in geothermal power plants as a temperature sensor. thermoelement

When moving charges along a DC circuit, external forces acting inside the sources do work. Physical quantity equal to the ratio of work outside forces by moving the charge from the negative pole of the current source to the positive to the value of this charge, is called the electromotive force (EMF) of the source
The EMF of the current source is spent on overcoming the resistance of the internal and external circuits by electric current. That part of the EMF that is spent on overcoming the resistance of the external circuit is called the voltage on the external resistance, the part of the EMF that is spent on overcoming the resistance inside the current source is called the voltage on the internal resistance.

Each pole of the intermediate source is connected to one pole of the previous and subsequent sources. emf battery is equal to the algebraic sum of the emf. individual sources. i The sign is determined arbitrarily according to the selected direction of traversal of the contour (see figure). If during the bypass we move from the negative pole to the positive one, then For example, in the figure shown Internal resistance batteries r = r + r r n

Magnetoelectric, electromagnetic, electrodynamic and electrostatic voltmeters are measuring instruments. measuring device voltmeter. Symbol for a voltmeter on wiring diagram: When you turn on the voltmeter in electrical circuit two rules must be observed: 1. The voltmeter is connected in parallel with the section of the circuit where the voltage will be measured; 2. We observe the polarity: the "+" of the voltmeter is connected to the "+" of the current source, and the "minus" of the voltmeter is connected to the "minus" of the current source. ___ To measure the voltage of a power source, a voltmeter is attached directly to its terminals.

Shunts and additional resistances. Shunt - a resistance connected in parallel to an ammeter (galvanometer) to expand its scale when measuring current. If the ammeter is designed for current I 0, and with it it is necessary to measure the current strength that is n times the allowable value, then the resistance of the connected shunt must satisfy the following condition: Additional resistance - resistance connected in series with a voltmeter (galvanometer) for expansion its scale when measuring voltage. If the voltmeter is designed for voltage U 0, and with it it is necessary to measure a voltage that is n times the permissible value, then the additional resistance must satisfy the following condition:

1. Formula for determining the current strength? AI=qt BI=t/q BI=q/t GI=qt 2 2. What is the name of the device for measuring the magnitude of the current? AAmmeter BVoltmeter VDynamometer GGalvanometer 3. What formula can determine the voltage? AU=A/I BU=A/q BU=q/A GU=Aq 4.Voltage unit? AAmp BOM VCoulomb GVolt 5. A device used to change the resistance in the circuit? Aresistor BKey VReostat GThere are no correct answers among the answers 6. Which of the formulas determines the resistance of a conductor? AR=pl/s BR=sp/l BR=s/pl GR=l/ps Answer the test questions.

memorize the formula for calculating the current strength;
learn to determine the strength of the current.

Current strength. Unit of current

Movement of a charge when a charged particle moves along an electric circuit

Current strength. Unit of current

The current strength is the charge passing through the cross section of the conductor in 1s.

Current strength. Unit of current

The interaction of two conductors with current is the basis for determining the unit of current strength.

1 amp – the current strength at which segments of parallel conductors 1 m long interact in vacuum with a force of 0.0000002 N.

Current strength. Unit of current

André Marie Ampère (1775-1836) French physicist and mathematician

Distinguishes between two concepts: current and voltage;

Sets current direction in a closed circuit;
Parallel conductors with currents flowing in one direction attract, and in the opposite direction they repel.

Current strength. Unit of current

Longitudinal and multiple units of current strength

Milliamp (mA)

1mA= 0.001 A

Microamp (µA)

1uA = 0.000001 A

Kiloampere (kA)

1kA = 1000 A

Current strength. Unit of current

Electric charge (amount of electricity)

1 pendant = 1 ampere × 1 second

1Kl = 1A ∙ 1 s = 1 A s

q = I∙t

Two charges of 1 C each at a distance of 1 m will interact with a force

9 ∙ 10 9 N!

Passes through your apartment in 1s charge ≈10C
When rubbing the comb, you get a charge of about 10 -8 cl

Current strength. Unit of current

Current strengths in practice

current in the bulb ≈ 2A
in an electric vacuum cleaner ≈ 0.25 A
in an electric shaver ≈ 0.1 A
in the electric locomotive engine ≈ 350 A
in lightning ≈ 10 6 BUT

The current strength of more than 100mA leads to damage to the body!

Only less than 1mA is safe.

Current strength. Unit of current

How to measure current strength?

A device for measuring current strength-AMMETER.

Connected in series

1. What is the current strength of the ammeter?

Consider Figure 137 and answer questions.

1.5 A; 2. 3 A; 3.0.5 BUT; 4. 2 A; 5.4 A.

2. What is the value of division of the ammeter scale?

1. 0.2 A; 2. 2 A; 3. 0.5 A ; 4. 4 A; 5. 0.1 A.

3. What is the current strength in the circuit?

4. Will the ammeter reading change, if it is turned on elsewhere in the same circuit, for example, between a current source and a switch?

1. 1.5 A; 2.2.5 BUT ; 3. 0.5 A; 4. 2 A; 5. 0.2 A.

5. How is the current directed in an electric lamp?

1. Will not change. 2. Increase. 3. Decrease.

1. From a to b. 2. From b to a.

Look at picture 137 and answer the questions.

Determine the current strength in an electric lamp if 5 C of electricity passes through it in 10 s.

A. 50 A; B. 0.5 A; B. 2A.

What charge passes through a vacuum cleaner that has been running for 10 minutes if the current in the conductive cord is 5 A?

A. 50 C; B. 300 C; V. 3000 C.

How much electricity flows through the coil of a galvanometer, connected to the circuit for 2 minutes, if the current in the circuit is 12 mA? A. 0.024 C; B. 1.44 C; V. 24 C.

four . The current in the wires of your apartment in the evening is 10 A. What charge will pass through your apartment in 1 hour? And how many electrons?

Anchoring

What is current strength...
What determines the strength of the current ...
The unit of current ....
What is electric charge...

Current strength. Current units

Homework

§ 37 read and answer the questions orally.
Exercise 14 (1.2) in writing.
Topics for messages:

Man and lightning.

(On the effect of lightning on a person)

Who is to blame, what to do.

(On the rules of conduct during a thunderstorm)

Ball lightning. (Publications from the media)

Current strength. Current units

Well done, thanks for your attention!

Current strength. Current units

slide 2

slide 3

An electric current is called an ordered (directed) movement of charged particles. An electric current arises from the ordered movement of free electrons and ions. If you move a neutral body as a whole, then, despite the orderly movement of a huge number of electrons and atomic nuclei, an electric current does not arise. The total charge transferred through any section of the conductor will then be equal to zero, since charges of different signs move with the same average speed.

slide 4

Electric current has a certain direction. The direction of movement of positively charged particles is taken as the direction of the current. If the current is formed by the movement of negatively charged particles, then the direction of the current is considered opposite to the direction of movement of the particles. (Such a choice of the direction of the current is not very successful, since in most cases the current is the movement of electrons - negatively charged particles. The choice of the direction of the current was made at a time when nothing was known about free electrons in metals.

slide 5

We do not directly see the motion of particles in a conductor. The presence of an electric current has to be judged by the actions or phenomena that accompany it. First, the conductor through which the current flows heats up. Secondly, the electric current can change the chemical composition of the conductor, for example, release its chemical constituents (copper from a solution of copper sulphate, etc.). Thirdly, the current has a force effect on neighboring currents and magnetized bodies. This action of current is called magnetic. So, the magnetic needle near the current-carrying conductor rotates. The magnetic effect of the current, in contrast to the chemical and thermal ones, is the main one, since it manifests itself in all conductors without exception. The chemical effect of the current is observed only in solutions and melts of electrolytes, and heating is absent in superconductors. Current action

slide 6

If an electric current is established in the circuit, then this means that an electric charge is constantly transferred through the cross section of the conductor. The charge transferred per unit of time serves as the main quantitative characteristic of the current, called the current strength. If a charge ∆q is transferred through the cross section of the conductor during the time ∆t, then the current strength is equal to: Current strength

Slide 7

Thus, the current strength is equal to the ratio of the charge ∆q transferred through the cross section of the conductor during the time interval ∆t to this time interval. If the current strength does not change with time, then the current is called constant. Current strength, like charge, is a scalar quantity. It can be both positive and negative. The sign of the current strength depends on which of the directions along the conductor is taken as positive. Current strength I>0 if the direction of the current coincides with the conditionally chosen positive direction along the conductor. Otherwise I

Slide 8

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