How to find the internal resistance of a voltage source. Radio communication

Purpose of the work: study the method of measuring EMF and internal resistance of a current source using an ammeter and voltmeter.

Equipment: metal tablet, current source, ammeter, voltmeter, resistor, key, clamps, connecting wires.

To measure the EMF and internal resistance of the current source, an electrical circuit is assembled, the diagram of which is shown in Figure 1.

An ammeter, resistance and switch connected in series are connected to the current source. In addition, a voltmeter is also connected directly to the output jacks of the source.

EMF is measured by reading a voltmeter with the switch open. This method of determining EMF is based on a corollary from Ohm’s law for complete chain, according to which, with an infinitely large resistance of the external circuit, the voltage at the source terminals is equal to its emf. (See the paragraph "Ohm's Law for a Complete Circuit" in the Physics 10 textbook).

To determine the internal resistance of the source, key K is closed. In this case, two sections can be conventionally distinguished in the circuit: external (the one that is connected to the source) and internal (the one that is located inside the current source). Since the source EMF is equal to the sum of the voltage drops in the internal and external sections of the circuit:

ε = Ur+UR, ThatUr = ε -UR (1)

According to Ohm's law for a section of the chain U r = I · r(2). Substituting equality (2) into (1) we get:

I· r = ε - Ur , whence r = (ε - UR)/ J

Therefore, to find out internal resistance current source, you must first determine its EMF, then close the switch and measure the voltage drop across the external resistance, as well as the current strength in it.

Work progress

1. Prepare a table to record the results of measurements and calculations:

ε ,V	U r , B	i,a	r , Ohm

Draw a diagram in your notebook to measure the emf and internal resistance of the source.

After checking the circuit, assemble the electrical circuit. Unlock the key.

Measure the magnitude of the source emf.

Close the key and determine the readings of the ammeter and voltmeter.

Calculate the internal resistance of the source.

Determination of emf and internal resistance of a current source by graphical method

Purpose of the work: study the measurements of emf, internal resistance and short circuit current of the current source, based on the analysis of the graph of the dependence of the voltage at the output of the source on the current in the circuit.

Equipment: galvanic cell, ammeter, voltmeter, resistor R 1 , variable resistor, key, clamps, metal tablet, connecting wires.

From Ohm’s law for a complete circuit it follows that the voltage at the output of the current source depends in direct proportion to the current in the circuit:

since I =E/(R+r), then IR + Ir = E, but IR = U, whence U + Ir = E or U = E – Ir (1).

If you plot the dependence of U on I, then from its points of intersection with the coordinate axes you can determine E, I K.Z. - current strength short circuit(current that will flow in the source circuit when the external resistance R becomes zero).

EMF is determined by the point of intersection of the graph with the voltage axis. This point on the graph corresponds to the state of the circuit in which there is no current in it and, therefore, U = E.

The strength of the short circuit current is determined by the point of intersection of the graph with the current axis. In this case, the external resistance R = 0 and, therefore, the voltage at the source output U = 0.

The internal resistance of the source is found by the tangent of the angle of inclination of the graph relative to the current axis. (Compare formula (1) with a mathematical function of the form Y = AX + B and remember the meaning of the coefficient for X).

Work progress

To record the measurement results, prepare a table:

After the teacher checks the circuit, assemble the electrical circuit. Set the variable resistor slider to the position at which the resistance of the circuit connected to the current source is maximum.

Determine the current in the circuit and the voltage at the source terminals at the maximum resistance value of the variable resistor. Enter the measurement data into the table.

Repeat current and voltage measurements several times, decreasing the value each time variable resistance so that the voltage at the source terminals decreases by 0.1V. Stop measurements when the current in the circuit reaches 1A.

Plot the points obtained in the experiment on a graph. Plot voltage along the vertical axis, and current along the horizontal axis. Draw a straight line through the points.

Continue the graph until it intersects with the coordinate axes and determine the values of E and I K.Z.

Measure the EMF of the source by connecting a voltmeter to its terminals with the external circuit open. Compare the EMF values obtained by the two methods and indicate the reason for the possible discrepancy in the results.

Determine the internal resistance of the current source. To do this, calculate the tangent of the angle of inclination of the constructed graph to the current axis. Since the tangent of an angle in a right triangle is equal to the ratio of the opposite side to the adjacent side, this can practically be done by finding the ratio E / I K.Z

Let's say there is a simple electrical closed circuit, which includes a current source, for example a generator, a galvanic cell or a battery, and a resistor with a resistance R. Since the current in the circuit is not interrupted anywhere, it flows inside the source.

In such a situation, we can say that any source has some internal resistance that prevents current flow. This internal resistance characterizes the current source and is designated by the letter r. For a battery, internal resistance is the resistance of the electrolyte solution and electrodes; for a generator, it is the resistance of the stator windings, etc.

Thus, the current source is characterized by both the magnitude of the EMF and the value of its own internal resistance r - both of these characteristics indicate the quality of the source.

Electrostatic high-voltage generators (like the Van de Graaff generator or the Wimshurst generator), for example, are distinguished by a huge EMF measured in millions of volts, while their internal resistance is measured in hundreds of megaohms, which is why they are unsuitable for producing large currents.

Galvanic elements (such as a battery), on the contrary, have an EMF of the order of 1 volt, although their internal resistance is of the order of fractions or, at most, tens of ohms, and therefore currents of units and tens of amperes can be obtained from galvanic elements.

This diagram shows a real source with an attached load. Its internal resistance, as well as the load resistance, are indicated here. According to, the current in this circuit will be equal to:

Since the section of the external circuit is homogeneous, the voltage across the load can be found from Ohm’s law:

Expressing the load resistance from the first equation and substituting its value into the second equation, we obtain the dependence of the load voltage on the current in a closed circuit:

In a closed loop, the EMF is equal to the sum of the voltage drops across the elements of the external circuit and the internal resistance of the source itself. The dependence of load voltage on load current is ideally linear.

The graph shows this, but experimental data on a real resistor (crosses near the graph) always differ from the ideal:

Experiments and logic show that at zero load current, the voltage on the external circuit is equal to the source emf, and at zero load voltage, the current in the circuit is equal to . This property of real circuits helps to experimentally find the emf and internal resistance of real sources.

Experimental determination of internal resistance

To experimentally determine these characteristics, plot the dependence of the voltage on the load on the current value, then extrapolate it to the intersection with the axes.

At the point of intersection of the graph with the voltage axis is the value of the source emf, and at the point of intersection with the current axis is the value of the short circuit current. As a result, the internal resistance is found by the formula:

Developed by source useful power stands out under load. The dependence of this power on the load resistance is shown in the figure. This curve starts from the intersection of the coordinate axes at the zero point, then increases to maximum value power, after which it drops to zero when the load resistance is equal to infinity.

To find the maximum load resistance at which the maximum power will theoretically develop at a given source, the derivative of the power formula with respect to R is taken and set equal to zero. Maximum power will develop when the external circuit resistance is equal to the internal resistance of the source:

This provision about the maximum power at R = r allows us to experimentally find the internal resistance of the source by plotting the dependence of the power released on the load on the value of the load resistance. Having found the real, and not theoretical, load resistance that provides maximum power, determine the real internal resistance of the power source.

The efficiency of a current source shows the ratio of the maximum power released at the load to full power, which in at the moment develops

Two-terminal network and its equivalent circuit

The internal resistance of a two-terminal network is the impedance in the equivalent circuit of a two-terminal network, consisting of a voltage generator and impedance connected in series (see figure). The concept is used in circuit theory when replacing a real source with ideal elements, that is, when moving to an equivalent circuit.

Introduction

Let's look at an example. In a passenger car, we will power the on-board network not from a standard lead-acid battery with a voltage of 12 volts and a capacity of 55 Ah, but from eight batteries connected in series (for example, AA size, with a capacity of about 1 Ah). Let's try to start the engine. Experience shows that when powered by batteries, the starter shaft will not turn a single degree. Moreover, even the solenoid relay will not work.

It is intuitively clear that the battery is “not powerful enough” for such an application, however, consideration of its declared electrical characteristics- voltage and charge (capacitance) - does not provide a quantitative description of this phenomenon. The voltage is the same in both cases:

Battery: 12 volts

Galvanic cells: 8·1.5 volts = 12 volts

The capacity is also quite sufficient: one ampere hour in the battery should be enough to rotate the starter for 14 seconds (at a current of 250 amperes).

It would seem that, in accordance with Ohm's law, the current in the same load with electrically identical sources should also be the same. However, in reality this is not entirely true. The sources would behave the same if they were ideal voltage generators. To describe the degree to which real sources differ from ideal generators and the concept of internal resistance is applied.

Resistance and internal resistance

The main characteristic of a two-terminal network is its resistance (or impedance). However, it is not always possible to characterize a two-terminal network with resistance alone. The fact is that the term resistance is applicable only to purely passive elements, that is, those that do not contain energy sources. If a two-terminal network contains an energy source, then the concept of “resistance” is simply not applicable to it, since Ohm’s law in the formulation U=Ir is not satisfied.

Thus, for two-terminal networks containing sources (that is, voltage generators and current generators), it is necessary to talk specifically about internal resistance (or impedance). If a two-terminal network does not contain sources, then “internal resistance” for such a two-terminal network means the same thing as simply “resistance”.

Related terms

If in any system it is possible to distinguish an input and/or an output, then the following terms are often used:

Input resistance is the internal resistance of the two-terminal network, which is the input of the system.

Output resistance is the internal resistance of the two-terminal network, which is the output of the system.

Physical principles

Despite the fact that in the equivalent circuit the internal resistance is presented as one passive element (and active resistance, that is, a resistor is necessarily present in it), the internal resistance is not concentrated in any one element. The two-terminal network only outwardly behaves as if it had a concentrated internal impedance and a voltage generator. In reality, internal resistance is an external manifestation of a set of physical effects:

If in a two-terminal network there is only an energy source without any electrical circuit (for example, a galvanic cell), then the internal resistance is purely active, it is caused by physical effects that do not allow the power supplied by this source to the load to exceed a certain limit. The simplest example of such an effect is the non-zero resistance of the conductors of an electrical circuit. But, as a rule, the greatest contribution to power limitation comes from non-electrical effects. So, for example, in a chemical source, the power can be limited by the contact area of the substances participating in the reaction, in a hydroelectric power station generator - by limited water pressure, etc.

In the case of a two-terminal network containing inside electrical diagram, the internal resistance is “dispersed” in the circuit elements (in addition to the mechanisms listed above in the source).

This also implies some features of internal resistance:

Internal resistance cannot be removed from a two-terminal network

Internal resistance is not a stable value: it can change when any external conditions change.

The influence of internal resistance on the properties of a two-terminal network

The effect of internal resistance is an integral property of any two-terminal network. The main result of the presence of internal resistance is the limitation electrical power, which can be obtained in a load powered from this two-terminal network.

If a load with resistance R is connected to a source with an emf of a voltage generator E and an active internal resistance r, then the current, voltage and power in the load are expressed as follows.

Calculation

The concept of calculation applies to a circuit (but not to real device). The calculation is given for the case of purely active internal resistance (differences in reactance will be discussed below).

Let there be a two-terminal network, which can be described by the equivalent circuit given above. A two-terminal network has two unknown parameters that need to be found:

EMF voltage generator U

Internal resistance r

In general, to determine two unknowns, it is necessary to make two measurements: measure the voltage at the output of a two-terminal network (that is, the potential difference Uout = φ2 − φ1) at two different load currents. Then the unknown parameters can be found from the system of equations:

where Uout1 is the output voltage at current I1, Uout2 is the output voltage at current I2. By solving the system of equations, we find the unknown unknowns:

Typically, more than simple technique: voltage is in mode idle speed and current in the short circuit mode of a two-terminal network. In this case, system (1) is written as follows:

where Uoc is the output voltage in open circuit mode, that is, at zero load current; Isc - load current in short circuit mode, that is, with a load with zero resistance. It is taken into account here that the output current in no-load mode and the output voltage in short-circuit mode are zero. From the last equations we immediately get:

Measurement

The concept of measurement applies to a real device (but not to a circuit). Direct measurement with an ohmmeter is impossible, since it is impossible to connect the probes of the device to the internal resistance terminals. Therefore, an indirect measurement is necessary, which is not fundamentally different from calculation - voltages across the load are also required at two different current values. However, it is not always possible to use the simplified formula (2), since not every real two-terminal network allows operation in short circuit mode.

The following simple measurement method that does not require calculations is often used:

Open circuit voltage is measured

A variable resistor is connected as a load and its resistance is selected so that the voltage across it is half the open circuit voltage.

After the described procedures, the resistance of the load resistor must be measured with an ohmmeter - it will be equal to the internal resistance of the two-terminal network.

Whatever measurement method is used, one should be wary of overloading the two-terminal network with excessive current, that is, the current should not exceed the maximum permissible value for a given two-terminal network.

Reactive internal resistance

If the equivalent circuit of a two-terminal network contains reactive elements - capacitors and/or inductors, then the calculation of the reactive internal resistance is performed in the same way as the active one, but instead of the resistances of resistors, the complex impedances of the elements included in the circuit are taken, and instead of voltages and currents, their complex amplitudes are taken, that is, the calculation is performed by the complex amplitude method.

The internal reactance measurement has some special features because it is a complex-valued function rather than a scalar value:

You can search for various parameters of a complex value: modulus, argument, only the real or imaginary part, as well as the entire complex number. Accordingly, the measurement technique will depend on what we want to obtain.

The need to introduce the term can be illustrated by the following example. Let's compare two chemical sources DC with the same voltage:

Car lead-acid battery with a voltage of 12 volts and a capacity of 55 Ah
Eight AA batteries connected in series. The total voltage of such a battery is also 12 volts, the capacity is much smaller - approximately 1 Ah

Despite the same voltage, these sources differ significantly when operating at the same load. So, car battery capable of giving load high current(the car engine starts from the battery, while the starter consumes a current of 250 amperes), but from a chain of batteries the starter does not rotate at all. The relatively small capacity of the batteries is not the reason: one amp-hour in the batteries would be enough to rotate the starter for 14 seconds (at a current of 250 amps).

Thus, for two-terminal networks containing sources (that is, voltage generators and current generators), it is necessary to talk specifically about internal resistance (or impedance). If the two-terminal network does not contain sources, then “ internal resistance" for such a two-terminal network means the same as Just"resistance".

Related terms

If in any system it is possible to distinguish an input and/or an output, then the following terms are often used:

Physical principles

Despite the fact that in the equivalent circuit the internal resistance is presented as one passive element (and active resistance, that is, a resistor is necessarily present in it), the internal resistance is not concentrated in any one element. Two-terminal network only externally behaves as if it had a concentrated internal impedance and a voltage generator. In reality, internal resistance is an external manifestation of a set of physical effects:

If in a two-terminal network there is only energy source without any electrical circuit (for example, a galvanic cell), then the internal resistance is almost purely active (unless we are talking about very high frequencies), it is caused by physical effects that do not allow the power supplied by this source to the load to exceed a certain limit. The simplest example of such an effect is the non-zero resistance of the conductors of an electrical circuit. But, as a rule, the greatest contribution to power limitation comes from the effects non-electric nature. So, for example, in power it can be limited by the contact area of the substances participating in the reaction, in a hydroelectric power station generator - by limited water pressure, etc.
In the case of a two-terminal network containing inside electrical diagram, the internal resistance is “dispersed” in the circuit elements (in addition to the mechanisms listed above in the source).

This also implies some features of internal resistance:

The influence of internal resistance on the properties of a two-terminal network

The effect of internal resistance is an integral property of any active two-terminal network. The main result of the presence of internal resistance is to limit the electrical power that can be obtained in the load supplied from this two-terminal network.

Let there be a two-terminal network, which can be described by the above equivalent circuit. A two-terminal network has two unknown parameters that need to be found:

EMF voltage generator U
Internal resistance r

In general, to determine two unknowns, it is necessary to make two measurements: measure the voltage at the output of the two-terminal network (that is, the potential difference U out = φ 2 − φ 1) at two different load currents. Then the unknown parameters can be found from the system of equations:

(Voltages)

Where U out1 I 1, Uout2- output voltage at current I 2. By solving the system of equations, we find the unknown unknowns:

Typically, a simpler technique is used to calculate the internal resistance: the voltage in the no-load mode and the current in the short-circuit mode of the two-terminal network are found. In this case, system () is written as follows:

Where U oc- output voltage in idle mode (eng. open circuit), that is, at zero load current; Isc- load current in short circuit mode (eng. short circuit), that is, under a load with zero resistance. It is taken into account here that the output current in no-load mode and the output voltage in short-circuit mode are zero. From the last equations we immediately get:

(Internal Resistance)

Measurement

Concept measurement applicable to the real device (but not to the circuit). Direct measurement with an ohmmeter is impossible, since it is impossible to connect the probes of the device to the internal resistance terminals. Therefore, indirect measurement is necessary, which is not fundamentally different from calculation - voltages across the load are also required at two different current values. However, it is not always possible to use the simplified formula (2), since not every real two-terminal network allows operation in short circuit mode.

Sometimes the following simple measurement method is used, which does not require calculations:

Open circuit voltage is measured
A variable resistor is connected as a load and its resistance is selected so that the voltage across it is half the open circuit voltage.

After the described procedures, the resistance of the load resistor must be measured with an ohmmeter - it will be equal to the internal resistance of the two-terminal network.

Reactive internal resistance

If the equivalent circuit of a two-terminal network contains reactive elements - capacitors and/or inductors, then calculation Reactive internal resistance is performed in the same way as active resistance, but instead of resistor resistances, the complex impedances of the elements included in the circuit are taken, and instead of voltages and currents, their complex amplitudes are taken, that is, the calculation is made by the complex amplitude method.

Measurement reactance has some special features because it is a complex-valued function rather than a scalar value:

You can search for various parameters of a complex value: modulus, argument, only the real or imaginary part, as well as the entire complex number. Accordingly, the measurement technique will depend on what we want to obtain.
Any of the listed parameters depends on frequency. Theoretically, to obtain by measurement full information about internal reactive resistance, it is necessary to remove addiction on frequency, that is, carry out measurements at everyone frequencies that the source of a given two-terminal network can generate.

Application

In most cases, we should not talk about application internal resistance, and about accounting his negative influence, since internal resistance is rather a negative effect. However, in some systems a nominal internal resistance is essential.

Simplification of equivalent circuits

The representation of a two-terminal network as a combination of a voltage generator and internal resistance is the simplest and most frequently used equivalent circuit of a two-terminal network.

Source-Load Matching

Matching the source and load is the choice of the ratio of the load resistance and the internal resistance of the source in order to achieve the specified properties of the resulting system (as a rule, they try to achieve the maximum value of any parameter for this source). Most commonly used following types approvals:

Current and power matching should be used with caution as there is a risk of overloading the source.

High Voltage Reduction

Sometimes it is artificially added to the source high resistance(it is added to the internal resistance of the source) in order to significantly reduce the voltage received from it. However, adding a resistor as additional resistance (the so-called quenching resistor) leads to useless power being allocated to it. To avoid wasting energy, AC systems use reactive damping impedances, most often capacitors. This is how capacitor power supplies are built. Similarly, using a capacitive tap from a high-voltage power line, you can obtain small voltages to power any autonomous devices.

Minimizing noise

When amplified weak signals The problem often arises of minimizing the noise introduced by the amplifier into the signal. For this purpose special low noise amplifiers, however, they are designed in such a way that the lowest noise figure is achieved only within a certain range of the output impedance of the signal source. For example, a low noise amplifier provides minimal noise only over the source output impedance range of 1 kΩ to 10 kΩ; if the signal source has a lower output impedance (for example, a microphone with an output impedance of 30 Ohms), then a step-up transformer should be used between the source and the amplifier, which will increase the output impedance (as well as the signal voltage) to the required value.

Restrictions

The concept of internal resistance is introduced through an equivalent circuit, so the same restrictions apply as for the applicability of equivalent circuits.

Examples

Internal resistance values are relative: what is considered small, for example, for a galvanic cell, is very large for powerful battery. Below are examples of two-terminal networks and the values of their internal resistance r. Trivial cases of two-terminal networks no sources are specifically stated.

Low internal resistance

High internal resistance

Negative internal resistance

There are two-terminal networks whose internal resistance has negative meaning. In normal active resistance, energy dissipation occurs, in reactive In resistance, energy is stored and then released back to the source. The peculiarity of negative resistance is that it itself is a source of energy. Therefore, negative resistance does not occur in its pure form; it can only be simulated electronic circuit, which necessarily contains a source of energy. Negative internal resistance can be achieved in circuits by using:

elements with negative differential resistance, such as tunnel diodes

Systems with negative resistance are potentially unstable and therefore can be used to build self-oscillators.

Literature

Zernov N.V., Karpov V.G. Theory radio circuits. - M. - L.: Energy, 1965. - 892 p.
Jones M.H. Electronics - practical course. - M.: Tekhnosphere, 2006. - 512 p. ISBN 5-94836-086-5

Notes

Wikimedia Foundation. 2010.

Polytechnic terminological explanatory dictionary

In the age of electricity, there is probably no such person who would not know about the existence electric current. But few people remember more from a school physics course than the names of quantities: current, voltage, resistance, Ohm’s law. And only very few remember what the meaning of these words is.

In this article, we will discuss how electric current occurs, how it is transmitted through a circuit, and how to use this quantity in calculations. But before moving on to the main part, let us turn to the history of the discovery of electric current and its sources, as well as the definition of what electromotive force is.

Story

Electricity as a source of energy has been known since ancient times, because nature itself generates it in huge volumes. A striking example is lightning or an electric ramp. Despite such closeness to humans, it was possible to curb this energy only in the middle of the seventeenth century: Otto von Guericke, the burgomaster of Magdeburg, created a machine that allowed the generation of an electrostatic charge. In the mid-eighteenth century, Peter von Muschenbroek, a scientist from Holland, created the world's first electric capacitor, named the Leyden jar in honor of the university where he worked.

Perhaps, the era of real discoveries dedicated to electricity begins with the work of Luigi Galvani and Alessandro Volta, who studied, respectively, electrical currents in muscles and the emergence of current in so-called galvanic cells. Further research opened our eyes to the connection between electricity and magnetism, as well as to several very useful phenomena (such as electromagnetic induction), without which it is impossible to imagine our lives today.

But we will not delve into magnetic phenomena and will focus only on electrical ones. So, let's look at how electricity arises in galvanic cells and what it is all about.

What is a galvanic cell?

We can say that it produces electricity due to chemical reactions occurring between its components. The simplest galvanic cell was invented by Alessandro Volta and named after him as a voltaic column. It consists of several layers, alternating with each other: a copper plate, a conductive gasket (in the home version of the design, cotton wool moistened with salt water is used) and a zinc plate.

What reactions take place in it?

Let's take a closer look at the processes that allow us to generate electricity using a galvanic cell. There are only two such transformations: oxidation and reduction. When one element, the reducing agent, is oxidized, it gives up electrons to another element, the oxidizing agent. The oxidizing agent, in turn, is reduced by accepting electrons. In this way, charged particles move from one plate to another, and this, as is known, is called electric current.

And now let’s move smoothly to the main topic of this article - the EMF of the current source. And first, let's look at what this electromotive force (EMF) is.

What is EMF?

This quantity can be represented as the work of forces (namely “work”) performed when a charge moves along a closed electrical circuit. Very often they also make clarifications that the charge must necessarily be positive and unit. And this is an essential addition, since only under these conditions can electromotive force be considered an accurate measurable quantity. By the way, it is measured in the same units as voltage: volts (V).

EMF of current source

As you know, each battery or battery has its own resistance value that it can produce. This value, the emf of the current source, shows how much work is done by external forces to move charge along the circuit in which the battery or accumulator is connected.

It is also worth clarifying what type of current the source produces: direct, alternating or pulsed. Galvanic cells, including accumulators and batteries, always produce only direct electric current. The EMF of the current source in this case will be equal in magnitude to the output voltage at the contacts of the source.

Now it’s time to figure out why such a quantity as EMF is needed in general, and how to use it when calculating other quantities of an electrical circuit.

EMF formula

We have already found out that the EMF of the current source is equal to the work of external forces to move the charge. For greater clarity, we decided to write down the formula for this quantity: E=A external forces /q, where A is work, and q is the charge on which work was done. Please note that the total charge is taken, not the unit charge. This is done because we consider the work done by forces to move all charges in a conductor. And this ratio of work to charge will always be constant for a given source, since no matter how many charged particles you take, the specific amount of work for each of them will be the same.

As you can see, the formula for electromotive force is not so complicated and consists of only two quantities. It's time to move on to one of the main questions arising from this article.

Why is EMF needed?

It has already been said that EMF and voltage are actually the same quantities. If we know the values of the EMF and the internal resistance of the current source, then it will not be difficult to substitute them into Ohm’s law for a complete circuit, which looks like this: I=e/(R+r), where I is the current strength, e is the EMF, R is circuit resistance, r - internal resistance of the current source. From here we can find two characteristics of the circuit: I and R. It should be noted that all these arguments and formulas are valid only for a direct current circuit. In the case of formula variables will be completely different, since it obeys its own oscillatory laws.

But it still remains unclear what application the EMF of a current source has. In a circuit, as a rule, there are a lot of elements that perform their function. In any phone there is a board, which is also nothing more than an electrical circuit. And each such circuit requires a current source to operate. And it is very important that its EMF matches the parameters for all elements of the circuit. Otherwise, the circuit will either stop working or burn out due to high voltage inside her.

Conclusion

We think this article was useful for many. After all, in modern world It is very important to know as much as possible about what surrounds us. Including essential knowledge about the nature of electric current and its behavior inside circuits. And if you think there's such a thing as electrical circuit, is used only in laboratories and you are far from it, then you are very mistaken: all devices that consume electricity actually consist of circuits. And each of them has its own current source, which creates an EMF.