Electric current Project of an 8th grade student of Municipal Educational Institution “Secondary School No. 4”, Kimry Ilya Ustinova 201 4-2015

Electric current is the ordered (directed) movement of charged particles.

The current strength is equal to the ratio of the electric charge q passing through the cross section of the conductor to the time of its passage t. I= I - current strength (A) q- electric charge(Cl) t- time (s) g t

Unit of measurement of current strength The unit of current strength is the current strength at which sections of parallel conductors 1 m long interact with a force of 2∙10 -7 N (0.0000002 N). This unit is called AMPERE (A). -7

Ampere Andre Marie Born on January 22, 1775 in Polemiers near Lyon into an aristocratic family. He received a home education. He was engaged in research into the connection between electricity and magnetism (Ampère called this range of phenomena electrodynamics). Subsequently he developed the theory of magnetism. Ampère died in Marseille on June 10, 1836.

Ammeter Ammeter is a device for measuring current. The ammeter is connected in series with the device in which the current is measured.

Current measurement Electrical circuit Electrical circuit diagram

Voltage is a physical quantity that shows how much work an electric field does when moving a unit positive charge from one point to another. A q U=

The unit of measurement is taken as follows: electrical voltage at the ends of a conductor, in which the work of moving an electric charge of 1 C along this conductor is equal to 1 J. This unit is called VOLT (V)

Alessandro Volta is an Italian physicist, chemist and physiologist, one of the founders of the doctrine of electricity. Alessandro Volta was born in 1745, the fourth child in the family. In 1801 he received the title of count and senator from Napoleon. Volta died in Como on March 5, 1827.

Voltmeter A voltmeter is a device for measuring electrical voltage. The voltmeter is connected to the circuit parallel to the section of the circuit between the ends of which the voltage is measured.

Voltage measurement Electrical circuit diagram Electrical circuit

Electrical resistance Resistance is directly proportional to the length of the conductor, inversely proportional to its cross-sectional area and depends on the substance of the conductor. R = ρ ℓ S R- resistance ρ - resistivity ℓ - length of conductor S - cross-sectional area

The cause of resistance is the interaction of moving electrons with ions of the crystal lattice.

The unit of resistance is taken to be 1 ohm. the resistance of such a conductor in which, at a voltage at the ends of 1 volt, the current strength is equal to 1 ampere.

Ohm Georg OM (Ohm) Georg Simon (March 16, 1787, Erlangen - July 6, 1854, Munich), German physicist, author of one of the fundamental laws, Ohm began researching electricity. In 1852, Ohm received the post of full professor. Ohm died on July 6, 1854. In 1881, at the electrical engineering congress in Paris, scientists unanimously approved the name of the resistance unit - 1 Ohm.

Ohm's Law The current strength in a section of a circuit is directly proportional to the voltage at the ends of this section and inversely proportional to its resistance. I = u R

Determining conductor resistance R=U:I Measuring current and voltage Electrical circuit diagram

APPLICATION OF ELECTRIC CURRENT

Slide 2

Electric current is the ordered movement of charged particles. To get electricity in a conductor, you need to create an electric field in it. Under the influence of this field, charged particles that can move freely in this conductor will begin to move in the direction of the action of electrical forces on them. An electric current arises. 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. An electric field in conductors is created and can be maintained for a long time by sources of electric current.

Slide 3

Current source poles

There are different current sources, but in each of them work is done to separate positively and negatively charged particles. The separated particles accumulate at the poles of the current source. This is the name of the places to which conductors are connected using terminals or clamps. One pole of the current source is charged positively, and the other - negatively.

Slide 4

Current sources

In current sources, in the process of separating charged particles, mechanical work is converted into electrical work. For example, in an electrophore machine (see figure), mechanical energy is converted into electrical energy

Slide 5

Electric circuit and its components

In order to use the energy of electric current, you must first have a source of current. Electric motors, lamps, tiles, all kinds of electrical household appliances are called receivers or consumers of electrical energy.

Slide 6

Symbols used in diagrams

Electrical energy must be delivered to the receiver. To do this, the receiver is connected to a source of electrical energy by wires. To turn receivers on and off at the right time, keys, switches, buttons, and switches are used. The current source, receivers, closing devices connected to each other by wires make up the simplest electrical circuit. For there to be current in the circuit, it must be closed. If the wire breaks in some place, the current in the circuit will stop.

Slide 7

Scheme

Drawings that show methods of connecting electrical devices into a circuit are called diagrams. Figure a) shows an example of an electrical circuit.

Slide 8

Electric current in metals

Electric current in metals is the ordered movement of free electrons. Evidence that the current in metals is caused by electrons was the experiments of physicists from our country L.I. Mendelshtam and N.D. Papaleksi (see figure), as well as American physicists B. Stewart and Robert Tolman.

Slide 9

Metal lattice nodes

Positive ions are located at the nodes of the metal crystal lattice, and free electrons move in the space between them, i.e., not associated with the nuclei of their atoms (see figure). The negative charge of all free electrons is equal in absolute value to the positive charge of all lattice ions. Therefore, under normal conditions the metal is electrically neutral.

Slide 10

Electron movement

When an electric field is created in a metal, it acts on the electrons with some force and imparts acceleration in the direction opposite to the direction of the field strength vector. Therefore, in an electric field, randomly moving electrons are displaced in one direction, i.e. move in an orderly manner.

Slide 11

The movement of electrons is partly reminiscent of the drift of ice floes during ice drift...

When they, moving randomly and colliding with each other, drift along the river. The ordered movement of conduction electrons constitutes electric current in metals.

Slide 12

Action of electric current.

We can judge the presence of electric current in a circuit only by the various phenomena that electric current causes. Such phenomena are called current actions. Some of these actions are easy to observe experimentally.

Slide 13

Thermal effect of current...

...can be observed, for example, by connecting iron or nickel wire to the poles of a current source. At the same time, the wire heats up and, having lengthened, sags slightly. It can even be red hot. In electric lamps, for example, a thin tungsten wire is heated by current and produces a bright glow

Slide 14

The chemical effect of current...

... is that in some acid solutions, when an electric current passes through them, a release of substances is observed. Substances contained in the solution are deposited on electrodes immersed in this solution. For example, when current is passed through a solution of copper sulfate, pure copper will be released at a negatively charged electrode. This is used to obtain pure metals.

Slide 15

Magnetic effect of current...

... can also be observed experimentally. To do this, a copper wire covered with insulating material must be wound around an iron nail, and the ends of the wire must be connected to a current source. When the circuit is closed, the nail becomes a magnet and attracts small iron objects: nails, iron filings, filings. With the disappearance of the current in the winding, the nail is demagnetized.

Slide 16

Let us now consider the interaction between a current-carrying conductor and a magnet.

The picture shows a small frame hanging on threads, on which several turns of thin copper wire are wound. The ends of the winding are connected to the poles of the current source. Consequently, there is an electric current in the winding, but the frame hangs motionless. If the frame is now placed between the poles of the magnet, it will begin to rotate.

Slide 17

Direction of electric current.

Since in most cases we are dealing with electric current in metals, it would be reasonable to take the direction of movement of electrons in the electric field as the direction of the current in the circuit, i.e. assume that the current is directed from the negative pole of the source to the positive. The direction of the current was conventionally taken to be the direction in which positive charges move in the conductor, i.e. direction from the positive pole of the current source to the negative. This is taken into account in all the rules and laws of electric current.

Slide 18

Current strength. Units of current strength.

The electric charge passing through the cross section of the conductor in 1 s determines the current strength in the circuit. This means that the current strength is equal to the ratio of the electric charge q passing through the cross section of the conductor to the time of its passage t. Where I is the current strength.

Slide 19

Experience on the interaction of two conductors with current.

At the International Conference on Weights and Measures in 1948, it was decided to base the definition of the unit of current on the phenomenon of interaction of two conductors with current. Let's first get acquainted with this phenomenon experimentally...

Slide 20

Experience

The figure shows two flexible straight conductors located parallel to each other. Both conductors are connected to a current source. When a circuit is closed, current flows through the conductors, as a result of which they interact - they attract or repel, depending on the direction of the currents in them. The force of interaction between conductors and current can be measured; it depends on the length of the conductor, the distance between them, the environment in which the conductors are located, and the strength of the current in the conductors.

Slide 21

Units of current.

The unit of current is the current at which sections of such parallel conductors 1 m long interact with a force of 0.0000002 N. This unit of current is called ampere (A). Since it is named after the French scientist Andre Ampere.

When measuring current, the ammeter is connected in series with the device in which the current is measured. In a circuit consisting of a current source and a series of conductors connected so that the end of one conductor is connected to the beginning of another, the current strength in all sections is the same.

Slide 25

The current strength is very important characteristic electrical circuit. Those working with electrical circuits should know that a current of up to 1 Ma is considered safe for the human body. Current strength greater than 100 Ma leads to serious damage to the body.

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Slide 1

Physics teacher at Nevinnomyssk Energy Technical School Pak Olga Ben-Ser
"Electric current in gases"

Slide 2

The process of current flowing through gases is called an electrical discharge in gases. The breakdown of gas molecules into electrons and positive ions is called gas ionization
At room temperatures, gases are dielectrics. Heating a gas or irradiating it with ultraviolet, x-rays and other rays causes the ionization of atoms or molecules of the gas. The gas becomes a conductor.

Slide 3

Charge carriers arise only during ionization. Charge carriers in gases – electrons and ions
If ions and free electrons find themselves in an external electric field, then they begin to move in a direction and create an electric current in the gases.
Mechanism of electrical conductivity of gases

Slide 4

Non-self-sustaining discharge
The phenomenon of electric current flowing through a gas, observed only under the condition of some external influence on the gas, is called a non-self-sustaining electric discharge. If there is no voltage on the electrodes, the galvanometer connected to the circuit will show zero. With a small potential difference between the electrodes of the tube, charged particles begin to move, and a gas discharge occurs. But not all the resulting ions reach the electrodes. As the potential difference between the electrodes of the tube increases, the current in the circuit also increases.

Slide 5

Non-self-sustaining discharge
At a certain voltage, when all the charged particles formed in the gas by the ionizer per second reach the electrodes during this time. The current reaches saturation. Current-voltage characteristics of a non-self-sustaining discharge

Slide 6

The phenomenon of electric current passing through a gas, independent of external ionizers, is called an independent gas discharge in a gas. The electron, accelerated by the electric field, collides with ions and neutral molecules on its way to the anode. Its energy is proportional to the field strength and the mean free path of the electron. If the kinetic energy of the electron exceeds the work that must be done to ionize the atom, then when the electron collides with the atom, it is ionized, called electron impact ionization.
An avalanche-like increase in the number of charged particles in a gas can begin under the influence of a strong electric field. In this case, the ionizer is no longer needed.
Self discharge

Slide 7

Slide 8

Corona discharge is observed at atmospheric pressure in a gas located in a highly inhomogeneous electric field (near the tips, wires of lines high voltage etc.) the luminous area of ​​which often resembles a crown (that’s why it was called corona)
Types of self-discharge

Slide 9

Spark discharge - An intermittent discharge in a gas that occurs at high electric field strength (about 3MV/m) in air at atmospheric pressure. A spark discharge, unlike a corona discharge, leads to breakdown of the air gap. application: lightning, for igniting a combustible mixture in an internal combustion engine, electric spark processing of metals
Types of self-discharge

Slide 10

Arc discharge - (electric arc) a discharge in a gas that occurs at atmospheric pressure and a small potential difference between closely spaced electrodes, but the current strength in the electric arc reaches tens of amperes. Application: spotlight, electric welding, cutting refractory metals.
Types of self-discharge

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