Why there is internal resistance inside the source. Electromotive force

An electric current in a conductor arises under the influence of an electric field, forcing free charged particles to come into directional motion. Particle current creation - serious problem... To build such a device that will maintain the potential difference of the field for a long time in one state is a task, the solution of which was within the power of mankind only to late XVIII century.

First attempts

The first attempts to "accumulate electricity" for further research and use were made in Holland. German Ewald Jürgen von Kleist and Dutchman Peter van Muschenbruck, who conducted their research in the town of Leiden, created the world's first capacitor, later called the "Leiden bank".

The accumulation of electric charge has already taken place under the action of mechanical friction. It was possible to use the discharge through the conductor for a certain, rather short, period of time.

The victory of the human mind over such an ephemeral substance as electricity turned out to be revolutionary.

Unfortunately, the discharge (the electric current created by the capacitor) lasted so short that it could not create. In addition, the voltage supplied by the capacitor gradually decreases, which does not leave the possibility of obtaining a continuous current.

It was necessary to find another way.

First source

The Italian Galvani's experiments on "animal electricity" were an original attempt to find a natural source of current in nature. Hanging the legs of the prepared frogs on the metal hooks of the iron lattice, he drew attention to the characteristic reaction of the nerve endings.

However, Galvani's conclusions were denied by another Italian - Alessandro Volta. Interested in the possibility of obtaining electricity from animal organisms, he conducted a series of experiments with frogs. But his conclusion turned out to be the complete opposite previous hypotheses.

Volta drew attention to the fact that a living organism is only an indicator of an electric discharge. As the current flows, the muscles of the legs contract, indicating a potential difference. The source of the electric field was the contact of dissimilar metals. The farther apart they are in the series of chemical elements, the greater the effect.

Plates of dissimilar metals, laid with paper disks impregnated with an electrolyte solution, created the required potential difference for a long time. And even if it was not high (1.1 V), the electric current could be investigated long time... The main thing is that the tension remained unchanged for the same long time.

What's happening

Why is such an effect caused in the sources called "galvanic cells"?

Two metal electrodes placed in a dielectric play different roles. One supplies electrons, the other accepts them. The redox reaction process leads to the appearance of an excess of electrons on one electrode, which is called the negative pole, and a deficiency on the second, we will designate it as the positive pole of the source.

In the simplest galvanic cells, oxidation reactions take place on one electrode, and reduction reactions take place on the other. Electrons arrive at the electrodes from the outside of the circuit. The electrolyte is the conductor of the ion current inside the source. The force of resistance controls the duration of the process.

Copper-zinc element

It is interesting to consider the principle of operation of galvanic cells using the example of a copper-zinc galvanic cell, the action of which is due to the energy of zinc and copper sulfate. In this source, a copper plate is placed in a solution and a zinc electrode is immersed in a zinc sulfate solution. The solutions are separated by a porous spacer to avoid mixing, but must be in contact.

If the circuit is closed, the surface layer of zinc is oxidized. In the process of interacting with a liquid, zinc atoms, having turned into ions, appear in the solution. Electrons are released on the electrode, which can take part in the formation of current.

When electrons hit the copper electrode, they take part in the reduction reaction. Copper ions come from the solution to the surface layer; during the reduction process, they turn into copper atoms, being deposited on the copper plate.

To summarize what is happening: the process of operation of a galvanic cell is accompanied by the transition of electrons from the reducing agent to the oxidizing agent along the outer part of the circuit. Reactions are going on at both electrodes. An ionic current flows inside the source.

Difficulties of use

In principle, any of the possible redox reactions can be used in batteries. But there are not so many substances capable of working in technically valuable elements. Moreover, many reactions require expensive substances.

Modern rechargeable batteries have a simpler structure. Two electrodes, placed in one electrolyte, fill the vessel - the battery case. Such design features simplify the structure and reduce the cost of batteries.

Any galvanic cell is capable of generating direct current.

The resistance of the current does not allow all the ions to be on the electrodes at the same time, so the element works for a long time. Chemical reactions of ion formation sooner or later stop, the element is discharged.

The current source is of great importance.

A little about resistance

Usage electric current undoubtedly deduced scientific and technical progress on new step gave him a giant boost. But the force of resistance to the flow of current gets in the way of such development.

On the one hand, electric current has invaluable properties used in everyday life and technology, on the other, there is significant opposition. Physics as a science of nature tries to establish a balance, to bring these circumstances into conformity.

Current resistance arises due to the interaction of electrically charged particles with the substance through which they move. Eliminate this process in normal temperature conditions impossible.

Resistance

The current source and the opposition of the external part of the circuit are of a slightly different nature, but the same in these processes is the work done to move the charge.

The work itself depends only on the properties of the source and its filling: the qualities of the electrodes and electrolyte, as well as for the external parts of the circuit, the resistance of which depends on the geometric parameters and chemical characteristics of the material. For example, the resistance of a metal wire increases as its length increases and decreases as its cross-sectional area expands. When solving the problem of how to reduce resistance, physics recommends using specialized materials.

Work current

In accordance with the Joule-Lenz law, an amount of heat is released in conductors proportional to the resistance. If the amount of heat is indicated by Q int. , current I, time of its flow t, then we get:

Q int. = I 2 r t,

where r is the internal resistance of the current source.

In the entire circuit, including both its internal and external parts, the total amount of heat will be released, the formula of which is:

Q total = I 2 r t + I 2 R t = I 2 (r + R) t,

It is known how resistance is denoted in physics: an external circuit (all elements except the source) has a resistance R.

Ohm's law for a complete circuit

Let's take into account that the main work is done by external forces inside the current source. Its value is equal to the product of the charge carried by the field and the electromotive force of the source:

q E = I 2 (r + R) t.

realizing that the charge is equal to the product current strength for the time of its flow, we have:

E = I (r + R).

In accordance with causal relationships, Ohm's law has the form:

I = E: (r + R).

In a closed circuit, it is directly proportional Source EMF current and is inversely proportional to the total (impedance) resistance of the circuit.

Based on this pattern, it is possible to determine the internal resistance of the current source.

Discharge capacity of the source

The main characteristics of the sources include the discharge capacity. The maximum amount of electricity that can be obtained during operation under certain conditions depends on the strength of the discharge current.

Ideally, when certain approximations are fulfilled, the discharge capacity can be considered constant.

For example, a standard battery with a potential difference of 1.5 V has a discharge capacity of 0.5 Ah. If the discharge current is 100mA, it will work for 5 hours.

Battery charging methods

Using batteries will drain them. small-sized cells are charged using a current whose strength does not exceed one tenth of the source capacity.

Offered following ways charging:

using a constant current for a given time (about 16 hours with a current of 0.1 battery capacity);
charging with a decreasing current to a predetermined value of the potential difference;
use of unbalanced currents;
sequential application of short pulses of charging and discharging, in which the time of the first exceeds the time of the second.

Practical work

The proposed task: to determine the internal resistance of the current source and EMF.

To complete it, you need to stock up on a current source, an ammeter, a voltmeter, a slide rheostat, a key, a set of conductors.

Use will determine the internal resistance of the current source. To do this, you need to know its EMF, the value of the resistance of the rheostat.

The calculated formula for the current resistance in the outer part of the circuit can be determined from Ohm's law for a section of the circuit:

I = U: R,

where I is the current in the outer part of the circuit, measured with an ammeter; U is the voltage across the external resistance.

To improve the accuracy, measurements are taken at least 5 times. What is it for? The voltage, resistance, current (or rather, the current strength) measured during the experiment are used further.

To determine the EMF of the current source, we will use the fact that the voltage at its terminals when the key is open is practically equal to the EMF.

Let's assemble a chain of batteries connected in series, a rheostat, an ammeter, a key. We connect a voltmeter to the terminals of the current source. Having opened the key, we take its readings.

The internal resistance, the formula of which is obtained from Ohm's law for a complete circuit, is determined by mathematical calculations:

I = E: (r + R).
r = E: I - U: I.

Measurements show that the internal resistance is much less than the external one.

The practical function of accumulators and batteries is widely used. Indisputable environmental Safety electric motors is beyond doubt, but creating a capacious, ergonomic battery is a problem in modern physics. Its solution will lead to a new round in the development of automotive technology.

Small, lightweight, high-capacity batteries are also essential in mobile electronic devices Oh. The supply of energy used in them is directly related to the performance of the devices.

At the ends of the conductor, and hence the current, the presence of external forces of a non-electrical nature is necessary, with the help of which the separation of electric charges occurs.

Outside forces are called any forces acting on electrically charged particles in the circuit, with the exception of electrostatic (i.e., Coulomb forces).

External forces set in motion charged particles inside all current sources: in generators, in power plants, in galvanic cells, batteries, etc.

When the circuit is closed, a electric field in all conductors of the chain. Inside the current source, charges move under the action of external forces against the Coulomb forces (electrons move from a positively charged electrode to a negative one), and in the rest of the circuit they are driven by an electric field (see the figure above).

In current sources, in the process of working to separate charged particles, a transformation occurs different types energy into electricity. By the type of converted energy, the following types of electromotive force are distinguished:

- electrostatic- in an electrophore machine, in which mechanical energy is converted into electrical energy during friction;

- thermoelectric- in a thermoelement - the internal energy of a heated junction of two wires made of different metals is converted into electrical energy;

- photovoltaic- in the photocell. Here, the transformation of light energy into electrical energy occurs: when illuminating certain substances, for example, selenium, copper (I) oxide, silicon, a loss of negative electrical charge is observed;

- chemical- in galvanic cells, batteries and other sources in which the conversion of chemical energy into electrical energy occurs.

Electromotive force (EMF)- characteristics of current sources. The concept of EMF was introduced by G. Ohm in 1827 for circuits direct current... In 1857 Kirchhoff defined EMF as the work of external forces during the transfer of a single electric charge along a closed circuit:

ɛ = A st / q,

where ɛ - EMF of the current source, A st- the work of outside forces, q- the amount of displaced charge.

The electromotive force is expressed in volts.

You can talk about the electromotive force at any part of the circuit. This is the specific work of external forces (work to move a unit charge) not in the entire circuit, but only in this area.

Internal resistance of the current source.

Let there be a simple closed circuit consisting of a current source (for example, a galvanic cell, battery or generator) and a resistor with a resistance R... The current in a closed circuit is not interrupted anywhere, therefore, it also exists inside the current source. Any source represents some resistance for the current. It's called internal resistance of the current source and denoted by the letter r.

In the generator r- this is the resistance of the winding, in a galvanic cell - the resistance of the electrolyte solution and electrodes.

Thus, the current source is characterized by the values of the EMF and internal resistance, which determine its quality. For example, electrostatic machines have a very high EMF (up to tens of thousands of volts), but their internal resistance is enormous (up to a hundred Mohm). Therefore, they are not suitable for receiving high currents. In galvanic cells, the EMF is only about 1 V, but on the other hand, the internal resistance is also low (about 1 Ohm or less). This makes it possible with their help to obtain currents measured in amperes.

We came to the conclusion that in order to maintain a constant current in a closed circuit, a current source must be included in it. Let us emphasize that the task of the source is not to supply charges to the electric circuit (there are enough of these charges in the conductors), but to make them move, to do the work of moving charges against the forces of the electric field. The main characteristic of the source is electromotive force 1 (EMF) - the work performed by external forces to move a single positive charge

Therefore, most people need associations or critical mass in the planetary field in order to receive energy signals and memories of consciousness and to be able to correctly perceive the signals. The 3D control system does not account for ascension symptoms, consciousness-related experiences, or many of the radical changes that people from this earth are experiencing. Grounding is a form of grounding on Earth and refers to direct contact bodies with elements of the Earth. This can be beneficial for many people who lack grounding and carnal discomfort during planetary changes.

The SI unit of EMF is Volt. The EMF of the source is equal to 1 volt if it does work 1 Joule when moving the charge 1 Coulomb

To designate current sources on electrical circuits, a special designation is used (Fig. 397).

rice. 397
The electrostatic field makes positive work on the movement of a positive charge in the direction of decreasing the field potential. The current source conducts separation of electric charges - positive charges accumulate on one pole, negative on the other. The strength of the electric field in the source is directed from the positive pole to the negative, so the work of the electric field to move the positive charge will be positive when it moves from "plus" to "minus". The work of external forces, on the contrary, is positive if positive charges move from the negative pole to the positive, that is, from "minus" to "plus".
This is the fundamental difference between the concepts of potential difference and EMF, which must always be remembered.
Thus, the electromotive force of the source can be considered an algebraic quantity, the sign of which ("plus" or "minus") depends on the direction of the current. In the circuit shown in fig. 398,

rice. 398
outside the source (in the external circuit) the current flows 2 from the "plus" of the source to the "minus", inside the source from "minus" to "plus". In this case, both external forces of the source and electrostatic forces in the external circuit do positive work.
If, in addition to electrostatic forces, external forces act on a certain section of the electrical circuit, then both electrostatic and external forces "work" on the movement of charges. The total work of electrostatic and external forces to move a single positive charge is called the electrical voltage in the circuit section

In the case when there are no external forces, the electric voltage coincides with the potential difference of the electric field.
Let us explain the definition of voltage and EMF sign on simple example... Let in the section of the circuit through which the electric current flows, there is a source of external forces and a resistor (Fig. 399).

rice. 399
For definiteness, we will assume that φ o> φ 1, that is, the electric current is directed from the point 0 to the point 1 ... When connecting the source as shown in fig. 399 a, External forces of the source do positive work, therefore, relation (2) in this case can be written in the form

When the source is switched back on (Fig. 399 b), the charges inside it move against external forces, so the work of the latter is negative. In fact, the forces of the external electric field overcome external forces. Therefore, in this case, the considered relation (2) has the form

For the flow of electric current through the section of the circuit that has electrical resistance, it is necessary to do work to overcome the forces of resistance. For a single positive charge, this work, according to Ohm's law, is equal to the product IR = U which naturally coincides with the voltage in this section.
Charged particles (both electrons and ions) inside the source move in some way, therefore, from the side of the medium, they are also affected by braking forces, which must also be overcome. Charged particles overcome resistance forces due to the action of external forces (if the current in the source is directed from "plus" to "minus") or due to electrostatic forces (if the current is directed from "minus" to "plus"). Obviously, the work to overcome these forces does not depend on the direction of movement, since the resistance forces are always directed in the direction opposite to the speed of movement of the particles. Since the forces of resistance are proportional average speed the movement of particles, then the work to overcome them is proportional to the speed of movement, therefore, to the strength of the current and force. Thus, we can introduce another characteristic of the source - its internal resistance r, similar to conventional electrical resistance. The work to overcome resistance forces when moving a single positive charge between the poles of the source is A / q = Ir... We emphasize once again that this work does not depend on the direction of the current in the source.

If you don't have access to nature and want to create an electrical circuit with the Earth's field, you can also use a primer that is associated with the human body. Electrical potential ground circuits depend on location, atmospheric conditions, time of day and night, and moisture on the surface of the earth. Intuitive empaths and star seedlings who want to restore energetic alignment with the planet's body should pay attention to their natural senses, because they need to know if they should be grounded or not.

1 The name of this physical quantity is unfortunate - so the electromotive force is work, and not force in the usual mechanical sense. But this term has become so entrenched that it is not "in our power to change it." By the way, the current strength is also not a mechanical force! Not to mention such concepts as "strength of mind", "willpower", "divine strength", etc.
2 Recall that the direction of movement of positive charges is taken as the direction of movement of the electric current.

In some cases, due to inorganic or external currents in certain areas, this practice may be impractical. For most people who are earth-seeded, justification will feel positively during the spiritual integration phase and will be very beneficial for the body because it will act as a neuromodulator. Neuromodulation is a process in which the activity of the nervous system is regulated by regulating physiological levels through stimulation of neurotransmitters. Thus, grounding changes the density of negative charge in the energy field of a person and his nervous system and directly affects physiological processes such as brain chemistry.

Laboratory work

"Measurement of EMF and internal resistance of the current source"

Discipline Physics

Lecturer Vinogradov A.B.

Nizhny Novgorod

Purpose of work: to form the ability to determine the EMF and internal resistance of the current source using an ammeter and a voltmeter.

The earth sends out electromagnetic signals to support human bodies in adapting to its ascension, and this signal allows the human nervous system to better adapt to the demands placed on the body and brain during intense changes in consciousness. When we want to restore the electrical balance of brain activity, it can be especially helpful to surround nature, focus on deep breathing, and connect with the Earth or the element of water.

The kidneys are the organs that supply energy. The human population is currently experiencing an epidemic of kidney disease caused by organ failure to adapt quickly to new circumstances, poor recognition of life-changing events, heart disease, toxic chemical overload and negative emotions. The purpose of the kidneys is to remove harmful metabolic products produced by bladder and maintaining proper blood chemistry and pressure as they control everything chemical substances dissolved in the bloodstream.

Equipment: rectifier VU-4M, ammeter, voltmeter, connecting wires, tablet number 1 elements: key, resistor R 1.

Theoretical The content of the work.

Internal resistance of the current source.

When current passes through closed circuit, electrically charged particles move not only inside the conductors connecting the poles of the current source, but also inside the current source itself. Therefore, in a closed electrical circuit, the external and internal sections of the circuit are distinguished. External section of the chain constitutes the entire set of conductors that is connected to the poles of the current source. Inner section of the chain is the current source itself. A current source, like any other conductor, has a resistance. Thus, in an electrical circuit consisting of a current source and conductors with electrical resistance R , the electric current does work not only on the external, but also on the internal section of the circuit. For example, when an incandescent lamp is connected to a galvanic battery of a flashlight, not only the lamp coil and the lead wires are heated with an electric current, but also the battery itself. The electrical resistance of the current source is called internal resistance. In an electromagnetic generator, the internal resistance is the electrical resistance of the generator winding wire. On the inner section of the electrical circuit, an amount of heat is released equal to

When the kidneys are weakened and overwhelmed, toxic waste products build up in the blood and tissues, as well as chemicals that cannot be properly filtered. Renal failure is increasing by 5% per year in the United States, with renal dialysis or transplantation being used as therapy. Ten percent of the population has some form of diabetes and neurological discomfort, and this number appears to be steadily increasing in both adults and children. What happened to our kidneys?

Eastern medical philosophy knows that the kidneys nourish other organs of the body. They act as the roots of life, which are responsible for protecting the body and distributing energy to all organs, reproductive functions and the entire body. The kidneys are the organs of relationships, so they suffer from problems with interpersonal and sexual relations, which can result from a lack of support from others or feelings of unloved, or even from a lack of physical sensitivity. Emotions circulate in your personal energy area, and when it is released, you may have a sense of flow through which you feel the emotions.

where r- internal resistance of the current source.

The total amount of heat released during the flow of direct current in a closed circuit, the external and internal sections of which have resistances, respectively equal R and r, equals

Any closed circuit can be represented as two series-connected resistors with equivalent resistances R and r... Therefore, the resistance of the complete circuit is equal to the sum of the external and internal resistances:

... Since at serial connection the current strength in all sections of the circuit is the same, then the same current flows through the outer and inner sections of the circuit. Then, according to Ohm's law for a section of the circuit, the voltage drop in its external and internal sections will be respectively equal:

It allows you to release emotional pain and fear and relieves you of chronic kidney problems by opening up greater emotional and spiritual energy expansion. When it is the other way around, when the heart is closed from pain and fear that blocks emotion, it interferes with the function of fluid management through the kidneys and disrupts the distribution of vital energy needed for a grounded, healthy and balanced mind and body.

Moreover, when our heart is healed, a flame burns inside, which also feeds vital energy stored in the kidneys. The triangular connector connects the heart to each kidney, which works like an electrical circuit in the luminous body. At the base of this triangle are the kidneys on the left and right, and the top point is associated with the heart. When the heart is healed, the flames in the heart and kidneys simultaneously activate the configuration of the heart in the inner double flame. The double flame corresponds to the restored energy balance between the energy of the male and the female, i.e. the structure of light created in the heart complex.

and

(3)

Electromotive force.

The total work of the forces of the electrostatic field during the movement of charges in a closed DC circuit is equal to zero. Consequently, all the work of the electric current in a closed electric circuit turns out to be perfect due to the action of external forces that cause the separation of charges inside the source and maintain a constant voltage at the output of the current source. Work attitude

performed by third-party forces to move the charge q along the chain, to the value of this charge is called electromotive force source(EMF) :

Therefore, when two fires are ignited in the heart, the vital essence stored in the kidneys helps carry the chi flame throughout the physical body to connect with the spiritual flame of the monadic body. Monad is a greater flame of the spirit, and physical body- lesser flame of life essence or life force. When these two fires ignite and combine, a flame explodes from the heart, which sends out fire to support the growth of the essence of life created by the kidneys. Basically, the kidneys help build the inner luminous body, which is necessary for the incorporation of the monadic body.

, (4)

- transportable charge.

EMF is expressed in the same units as voltage or potential difference, i.e. in volts:

Ohm's law for a complete circuit.

Any visual exercise designed to create life force energy in the lower dienes and induce energy to circulate at the base of the feet, strengthen the kidneys' ability to store vital essence, help correct the grounding mechanism and perform the functions of physical blood purification. There are some kidney and herbal potentiators that are common in oriental medicine and are useful for toning kidney function, especially if there is a problem with grounding or centering the core.

Renal failure causes adrenal production. The adrenal glands are glands that produce many hormones, and it is well known that under pressure they pump cortisol into the bloodstream, causing the human nervous system to go into a fight or flight state. Adrenaline is usually produced by both the adrenal glands and some neurons, which can also be activated by emotional responses. Each emotional response has a behavioral component, an autonomic nervous system component, a glandular secretion, or a hormonal factor.

If, as a result of the passage of direct current in a closed electric circuit, only the heating of the conductors occurs, then according to the law of conservation of energy full work electric current in a closed circuit, equal to the work of external forces of the current source, is equal to the amount of heat released in the external and internal sections of the circuit:

Hormonal factors associated with stress and emotional pain include the release of adrenaline and adrenal responses — in response to fear-based feelings controlled by the sympathetic nervous system. The main emotion that releases adrenaline into the bloodstream is fear.

In addition, the adrenal glands play an important role in responding to fight or flight by increasing blood flow to the muscles and heart, and then students expand and blood sugar levels rise. Adrenaline is pumped into the bloodstream when a person is provoked into terrorist attacks or fear in order to generate as much negative emotional energy as possible, which may be the main reason why the adrenal glands are completely depleted in most people. When a person does not correct this condition and is still pumping adrenaline or other stress hormones into the bloodstream, the nervous system freezes, a state of shock and numbness.

. (5)

From expressions (2), (4) and (5) we obtain:

. (6)

, then

, (7)

At some point, when you experience constant pain or fear due to an excessive load of adrenaline, the body and nervous system enter a state of numbness, which turns off emotional reactions by closing the heart. The adrenal glands are located at the top of each kidney, so they are directly prone to kidney depletion, which naturally causes the adrenal glands to drain. If we do something really unhealthy for our spirit and our daily work does not match who we are, it also depletes the kidneys, adrenaline and vitality.

. (8)

The current in an electrical circuit is directly proportional to the electromotive force. current source and is inversely proportional to the sum of the electrical resistances of the external and internal sections of the circuit. Expression (8) is called Ohm's law for a complete circuit.

When we have to deal with difficult stressors at work, in relationships, or in other situations, the body can be subjected to deep, unconscious emotional stress. We feel helpless and frustrated that we should simply work to meet financial obligations or to survive. Our body gives us a message due to excessive exhaustion that we can no longer live in the same way, we must make changes, and the first change must be to realize consciousness through the death of the ego.

Thus, from the point of view of physics, Ohm's Law expresses the law of conservation of energy for a closed DC circuit.

Work order.

Preparation for work.

There is a mini-laboratory on electrodynamics on the tables in front of you. Its appearance is presented in l. R. No. 9 in Figure 2.

On the left are a milliammeter, a VU-4M rectifier, a voltmeter, an ammeter. On the right, plate No. 1 is fixed (see Fig. 3 in sheet file No. 9). In the rear section of the case there are colored connecting wires: the red wire is used to connect the VU-4M to the "+" socket of the tablet; white wire - for connecting VU-4M to the "-" socket; yellow wires - for connecting measuring devices to the elements of the tablet; blue - to connect the elements of the tablet. The section is closed by a folding platform. In the working position, the platform is located horizontally and is used as a working surface when assembling experimental installations in experiments.

Planetary control of Chi's human kidneys. We must strive to restore the heart center and turn the kidneys into more high purpose associated with the ascension of the body. There are overlays encoding human bodies for enslavement, established at the time of birth, in the recording of the transduction sequence in the manifestation body of the nucleus or in the Tree of Life. The main manifestation template of the tree grid has a set of instructions to control the functions of organs and glands at the level of each dimension, as the glands secrete substances and hormones that allow the human consciousness to move faster between dimensions.

2. Progress of work.

As you work, you will master the method of measuring the basic characteristics of a current source using Ohm's law for a complete circuit, which relates the amperage I in the circuit, EMF of the current source , its internal resistance r and the resistance of the external circuit R ratio:

In the lands of the United Kingdom, the keys to awakening Albion's structures are hidden, and they are giant sleeping creatures. Tags are used to guide humans on Earth for future timelines to work in slave colonies or various galactic human trafficking sites that are controlled by these extraterrestrial corrupt conglomerates and dragon groups.

The Orion Black Sun Groups reserved the right to certain human bodies, genetic material, and the human Tree of Life, and that is why they control it. This makes it easier for them to control and monitor information related to soul structure and multidimensional anatomy. These are Draconians who steal from the spiritual parts of the body, as well as from organs and glands.

. (9)

1 way.

WITH The scheme of the experimental setup is shown in Figure 1.

Study it carefully. With open switch B, the source is closed to a voltmeter, the resistance of which is much greater than the internal resistance of the source (r R ). In this case, the current in the circuit is so small that the value of the voltage drop across the internal resistance of the source can be neglected.

, and the EMF of the source with negligible error is equal to the voltage at its terminals , which is measured with a voltmeter, i.e.

. (10)

Thus, the EMF of the source is determined by the readings of the voltmeter with open key V.

If the key B is closed, the voltmeter will show the voltage drop across the resistor R :

. (11)

Then, based on equalities (9), (10), and (11), we can assert that

(12)

It can be seen from formula (12) that in order to determine the internal resistance of the current source, it is necessary, in addition to its EMF, to know the current in the circuit and the voltage across the resistor R when the key is closed.

The current in the circuit can be measured using an ammeter. Wirewound resistor made of nichrome wire and has a resistance of 5 ohms.

Assemble the circuit according to the diagram shown in Figure 3.

After the circuit is assembled, you need to raise your hand, call the teacher to check the correct assembly of the electrical circuit. And if the chain is assembled correctly, then get down to work.

With open switch B, take readings of the voltmeter and enter the voltage value in table 1. Then close the key B and again take the voltmeter readings, but already and ammeter readings. Record the voltage and current values in table 1.

Formulate Ohm's law for the complete circuit.

If we did not know the values of the resistances of the wire resistors, would it be possible to use the second method and what needs to be done for this (maybe it is necessary, for example, to include some device in the circuit)?

Be able to collect electrical circuits used in the work.

Literature

Kabardin O. F .. Ref. Materials: Textbook. A handbook for students.-3rd ed. - M.: Education, 1991.-p.: 150-151.

Pupil's reference book. Physics / Comp. T. Feshchenko, V. Vozhegova. –M .: Philological society "SLOVO", LLC "Firma" "Publishing house AST", Center for the Humanities at the Faculty of Journalism, Moscow State University. M.V. Lomonosov, 1998 .-- p .: 124,500-501.

Samoilenko P.I .. Physics (for non-technical specialties): Textbook. for general education. institutions of environments. Prof. Education / P. I. Samoilenko, A. V. Sergeev.-2nd ed., Ster.-M .: Publishing Center "Academy", 2003-p .: 181-182.

A source is a device that converts mechanical, chemical, thermal and some other forms of energy into electrical energy. In other words, the source is an active network element designed to generate electricity. Various types The sources available on the power grid are voltage sources and current sources. These two concepts in electronics differ from each other.

Constant voltage source

The voltage source is a device with two poles, its voltage at any time is constant, and the current passing through it has no effect. Such a source would be ideal with zero internal resistance. In practical terms, it cannot be obtained.

An excess of electrons accumulates at the negative pole of the voltage source, and their deficit at the positive pole. The states of the poles are maintained by processes within the source.

Batteries

Batteries store chemical energy internally and are capable of converting it into electrical energy. The batteries cannot be recharged, which is a disadvantage.

Batteries

The batteries are rechargeable batteries. When charged, electrical energy is stored internally in the form of chemical energy. During unloading, the chemical process takes place in opposite direction and electrical energy is released.

Examples:

Lead acid battery cell. It is made from lead electrodes and an electrolytic liquid in the form of sulfuric acid diluted with distilled water. The voltage per cell is about 2 V. In car batteries, six cells are usually connected in a series circuit, at the output terminals the resulting voltage is 12 V;

Nickel-cadmium batteries, cell voltage - 1.2 V.

Important! At low currents, batteries and accumulators can be considered a good approximation to ideal voltage sources.

AC voltage source

Electricity is produced at power plants using generators and, after voltage regulation, is transmitted to the consumer. The alternating voltage of the home network of 220 V in the power supplies of various electronic devices is easily converted to a lower indicator when using transformers.

Power source

By analogy, as an ideal voltage source creates a constant voltage at the output, the task of the current source is to give a constant current value, automatically controlling the required voltage. Examples are current transformers (secondary winding), photocells, collector currents of transistors.

Calculation of the internal resistance of the voltage source

Real voltage sources have their own electrical resistance, which is called "internal resistance". The load connected to the source terminals is designated as "external resistance" - R.

The battery of accumulators generates EMF:

ε = E / Q, where:

E - energy (J);
Q - charge (Cl).

The total EMF of a battery cell is the voltage of its open circuit in the absence of a load. It can be checked with good accuracy with a digital multimeter. The potential difference measured at the output contacts of the battery, when it is connected to the load resistor, will be less than its voltage with an open circuit, due to the flow of current through the external load and through the internal resistance of the source, this leads to energy dissipation in it as thermal radiation ...

The internal resistance of a battery with a chemical principle of operation is between a fraction of an ohm and a few ohms and is mainly related to the resistance of the electrolytic materials used in the manufacture of the battery.

If a resistor of resistance R is connected to the battery, the current in the circuit is I = ε / (R + r).

Internal resistance is not constant. It is influenced by the type of battery (alkaline, lead acid, etc.) and varies with load value, temperature and battery life. For example, in disposable batteries, the internal resistance increases during use, and the voltage therefore drops until it reaches a state that is unsuitable for further use.

If the EMF of the source is a given value in advance, the internal resistance of the source is determined by measuring the current flowing through the load resistance.

Since the internal and external resistance in the approximate scheme are connected in series, you can use Ohm's and Kirchhoff's laws to apply the formula:

From this expression r = ε / I - R.

Example. A battery with a known EMF ε = 1.5 V and is connected in series with a light bulb. The voltage drop across the light bulb is 1.2 V. Therefore, the internal resistance of the element creates a voltage drop: 1.5 - 1.2 = 0.3 V. The resistance of the wires in the circuit is considered negligible, the resistance of the lamp is not known. The measured current passing through the circuit: I = 0.3 A. It is necessary to determine the internal resistance of the battery.

According to Ohm's law, the resistance of the light bulb is R = U / I = 1.2 / 0.3 = 4 Ohm;
Now, according to the formula for calculating the internal resistance r = ε / I - R = 1.5 / 0.3 - 4 = 1 Ohm.

In the event of a short circuit, the external resistance drops to almost zero. The current can limit its value only by a small resistance of the source. The strength of the current that occurs in such a situation is so great that the voltage source can be damaged by the thermal effect of the current, there is a danger of fire. The risk of fire is prevented by installing fuses, for example, in car battery circuits.

Internal resistance of the voltage source - important factor when deciding how to transfer the most effective power to the connected electrical appliance.

Important! Maximum power transfer occurs when the internal resistance of the source is equal to the resistance of the load.

However, under this condition, remembering the formula P = I² x R, an identical amount of energy is given to the load and dissipated in the source itself, and its efficiency is only 50%.

Load requirements must be carefully considered to decide whether to best use source. For example, a lead-acid car battery must provide high currents at a relatively low voltage of 12 V. Its low internal resistance allows it to do so.

In some cases, high voltage power supplies must have an extremely high internal resistance in order to limit the short-circuit current.

Features of the internal resistance of the current source

An ideal current source has infinite resistance, and for genuine sources, an approximate version can be presented. Equivalent circuitry is a resistance connected to the source in parallel and an external resistance.

The current output from the current source is distributed as follows: part of the current flows through the highest internal resistance and through the lowest load resistance.

The output current will be from the sum of the currents on the internal resistance and the load Iо = In + Ivn.

It turns out:

In = Iо - Ivn = Iо - Un / r.

This dependence shows that when the internal resistance of the current source increases, the more the current on it decreases, and the load resistor receives most current. Interestingly, the voltage will not affect the current value.

Real source output voltage:

Uout = I x (R x r) / (R + r) = I x R / (1 + R / r). Rate the article:

8.5. Thermal action current

8.5.1. Current source power

Apparent power of the current source:

P full = P useful + P losses,

where P useful - useful power, P useful = I 2 R; P losses - power losses, P losses = I 2 r; I is the current in the circuit; R - load resistance (external circuit); r is the internal resistance of the current source.

The apparent power can be calculated using one of three formulas:

P full = I 2 (R + r), P full = ℰ 2 R + r, P full = I ℰ,

where ℰ is the electromotive force (EMF) of the current source.

Net power is the power that is released in the external circuit, i.e. on the load (resistor), and can be used for some purpose.

Net power can be calculated using one of three formulas:

P useful = I 2 R, P useful = U 2 R, P useful = IU,

where I is the current in the circuit; U is the voltage at the terminals (clamps) of the current source; R - load resistance (external circuit).

Power dissipation is the power that is released in the current source, i.e. in the internal chain, and is spent on the processes taking place in the source itself; for any other purpose, the power loss cannot be used.

The power loss is usually calculated using the formula

P losses = I 2 r,

where I is the current in the circuit; r is the internal resistance of the current source.

In the event of a short circuit, the net power goes to zero

P useful = 0,

since there is no load resistance in the event of a short circuit: R = 0.

The apparent power at a short circuit of the source coincides with the power loss and is calculated by the formula

P full = ℰ 2 r,

where ℰ is the electromotive force (EMF) of the current source; r is the internal resistance of the current source.

The useful power has maximum value in the case when the load resistance R is equal to the internal resistance r of the current source:

R = r.

Maximum net power:

P useful max = 0.5 P full,

where P full is the total power of the current source; P full = ℰ 2/2 r.

Explicit formula for calculating maximum net power as follows:

P useful max = ℰ 2 4 r.

To simplify calculations, it is useful to keep two points in mind:

if, with two load resistances R 1 and R 2, the same useful power is released in the circuit, then internal resistance of the current source r is related to the indicated resistances by the formula

r = R 1 R 2;

if the maximum useful power is released in the circuit, then the current I * in the circuit is two times less than the short-circuit current i:

I * = i 2.

Example 15. With a short circuit to a resistance of 5.0 Ohm, the battery of cells gives a current of 2.0 A. The short-circuit current of the battery is 12 A. Calculate the maximum useful power of the battery.

Solution . Let's analyze the condition of the problem.

1. When the battery is connected to the resistance R 1 = 5.0 Ohm, a current of I 1 = 2.0 A flows in the circuit, as shown in fig. a, determined by Ohm's law for a complete circuit:

I 1 = ℰ R 1 + r,

where ℰ is the EMF of the current source; r is the internal resistance of the current source.

2. When the battery is short-circuited, the short-circuit current flows in the circuit as shown in fig. b. The short-circuit current is determined by the formula

where i is the short-circuit current strength, i = 12 A.

3. When the battery is connected to the resistance R 2 = r, a current of I 2 flows in the circuit, as shown in fig. in, determined by Ohm's law for a complete circuit:

I 2 = ℰ R 2 + r = ℰ 2 r;

in this case, the maximum useful power is released in the circuit:

P useful max = I 2 2 R 2 = I 2 2 r.

Thus, to calculate the maximum useful power, it is necessary to determine the internal resistance of the current source r and the current I 2.

In order to find the current strength I 2, we write down the system of equations:

i = ℰ r, I 2 = ℰ 2 r)

and perform the division of the equations:

i I 2 = 2.

This implies:

I 2 = i 2 = 12 2 = 6.0 A.

In order to find the internal resistance of the source r, we write down the system of equations:

I 1 = ℰ R 1 + r, i = ℰ r)