What values \u200b\u200bbinds the law of Ohm. Heating conductor electric shock. Law of Joule Lenza. Dependence of current and voltage
Tasks of the lesson: to comprehend the use of studied physical quantities and binding their values.
Objectives lesson:
- Students must assign that the amount of heat released by the conductor with the current is equal to the product of the current of the current force, the resistance of the conductor and time Q \u003d i? RT;
- Students must learn to solve problems for finding the amount of heat in specific situations;
- Fastening the skills of solving problems of settlement, high-quality
- and experimental;
- Formation of good faith in labor, positive
- relationships to knowledge, upbringing discipline, aesthetic views.
During the classes
Actualization of knowledge. Frontal survey.
1. What three values \u200b\u200bbind Ohm's law?
I, u, r; Current strength, voltage, resistance.
2. How is Ohm's law formulad?
The strength of the current in the section of the chain is directly proportional to the voltage at the ends of this section and is inversely proportional to its resistance.
3. How is the formula of the Ohm law record?
4. Units of measurement of physical quantities included in the Ohm law.
Ampere, Volt, Ohm.
5. How to express current operation for a while?
6. What is called power?
To find the average power of the electric current, it is necessary to work it to be divided for a time p \u003d a / t.
8. What are taken per unit of power?
The unit of measurement unit adopted 1 W equal to 1 j / s, 1 W \u003d 1J / s.
9. What are the conductor connections consistent?
10. What value is the same for all conductors connected in series?
Current strength, i \u003d i 1 \u003d i 2 \u003d i n
11. How to find a common chain resistance, knowing the resistance of individual conductors, with a sequential connection?
R \u003d R 1 + R 2 +: + R n.
12. How to find the voltage of the chain area consisting of consistently connected conductors, knowing the voltage on each of them?
U \u003d u 1 + U 2 +: + u n.
13. What is the connection of the conductors called parallel?
14. What size is the same for all conductors connected in parallel?
Voltage, u \u003d u 1 \u003d u 2 \u003d u n.
15. How to find the overall resistance of the chain, knowing the resistance of individual conductors, with a parallel connection?
R \u003d R 1 * R 2 * R n / (R 1 + R 2 + R n).
16. How to find the strength of the current on the chain area with a parallel connection?
I \u003d i 1 + i 2 + i n.
17. Electric shock called:
ordered movement of free electrons.
18. Formula for calculating the resistance of the conductor?
19. Ampmeter is included in the chain:
consistently.
20. All consumers are under the same tension at:
parallel connection.
21. Guess the riddle.
A very strict controller from the wall looks in the emphasis,
Looks without blinking. There is only light light,
Or turn on the oven in the outlet -
Everything on the mustache winds. (Electrospherchik).
And what winds on the "Us" electric meter?
Electric energy consumption.
Demonstration of the experiment.
Determining the power of the light bulb.
A \u003d u * i * T \u003d 2.6V * 1,4A * 240С \u003d 873.6 J.
Q \u003d C * M * (T 2 -T 1) \u003d 4200J / (kg * 0 s) * 0.1kg * 2 0 C \u003d 840 J.
Exercise 27 (2) from.
Question: For what purpose the wires in the connection places are not just twisted, but also solder? Justify the answer.
The power of the current in both wires is the same, since the conductors are connected in series.
If the contact location of two conductors is not fast, then its resistance will be quite large compared to the resistance of the conductors themselves. Then there will be the largest amount of warmth. This will lead to melting the contact location of two conductors and opening the electrical circuit.
The wording of the Law of Joule - Lenza.
The amount of heat released by the conductor with a current is equal to the product of the current of the current force, the resistance of the conductor and time.
Organization of independent activities of students.
I option.
1. How will the amount of heat released by the conductor with the current change, if the current is increased by 2 times in the conductor?
A. will increase by 2 times. B. will decrease by 2 times. B. will increase 4 times.
Answer. According to the law of Joule - Lenza Q \u003d i 2 * R * T, therefore will increase by 4 times.
B. will increase 4 times.
2. What amount of heat will allocate a wire spiral with a resistance of 20 ohm in 30 minutes, if the current is in the circuit 2a?
A. 144000 J. B. 28800 J. V. 1440 J.
Answer. A. 1440009.
3. Copper and nichrome wires having the same dimensions are connected in parallel and connected to the current source. Which one will allocate more warmth?
A. Nichromova. B. Copper. B. Equally.
Answer. B. Copper.
II option.
1. How will the amount of heat released by the conductor with a current change, if the current is 4 times reduced?
A. It will decrease by 2 times. B. decreases 16 times. B. will increase 4 times.
Answer. According to the law of Joule - Lenza Q \u003d I 2 * R * T, therefore will decrease 16 times.
B. decreases 16 times.
2. In the electric furnace at a voltage of 220 V, the current of the current 30 A. What amount of heat will allocate a stove in 10 minutes?
A. 40000 J. B. 39600 J. B. 3960000 J.
Answer. 3960000 J.
3. Nickeline and steel wires having the same dimensions are connected in series and connected to the current source. Which one will allocate more warmth.
A. Nickelinovaya. B. Steel. B. Equally.
Answer. Nickelinic.
Additional task.
Tasks from.
Answer. 500 J.
Homework.
Paragraph 53, UPR.27 (1, 3) from.
Bibliography:
- Textbook "Physics", grade 8. A.V. Pyryshkin.
- "Collection of tasks in physics." IN AND. Lukashik.
When the external circuit is connected to the source, the turkey field with a speed of light spreads along the conductor and free charges in them almost simultaneously come into an ordered movement. The circuit appears current.
The main laws of DC were established B1826-1827 by German scientist Georg Ohm and therefore carry his name.
Consider the inhomogeneous section of the chain where EDC is valid. EMF in section 1-2 denoted by ε 12, and the potential difference attached at the ends of the site - through φ 1 -φ 2. The operation of the forces A 12 (third-party and Coulomb), performed above the current carriers, according to the law of conservation and the conversion of energy is heat, Estimated on the site. The work of the forces committed when the charge is moving in the section 1-2 is equal
A 12 \u003d Q \u003d Q 0 ε 12 + Q 0 (φ 1 -φ 2) (13.12)
During the time in the conductor, heat is highlighted
from 
(13.14)
In this way, generalized Ohma Law,or Ohm law for heterogeneous section of chain (section of the chain containing the source of EDS), says:
The current of the current on the inhomogeneous section of the chain is directly proportional to the amount of EDC and the difference in potentials at the ends of this section and inversely proportional to its total resistance
(13.15)
where r - interior resistance The source of EMF, R resistance to the external chain.
Applying the generalized Ohma law to one or another active section of the chain, it should be pre-selected the direction of circumventing of this area, and there is one of its ends to be considered first (with the potential φ 1), and the other is second - (with the potential - φ 2). In the coincidence of this direction, with the direction of the current current of current, the current is considered positive (I\u003e 0), otherwise negative (I<0). ЭДС на рассматриваемом участке положительна тогда, когда направление обхода совпадает с направлением стороннего поля в источнике (это поле в нём направлено от отрицательного полюса к положительному); если же эти направления не совпадают, ЭДС считается отрицательной.
From the generalized law of Ohm, you can get two other laws.
Ohm law for closed ( or full) chain :
The strength of the current in a closed circuit is directly proportional to the EDC and inversely proportional to its total resistance
(13.16)
Since the ends of the closed circuit are connected, and the potentials φ 1 and φ 2 are becoming equal, then the potential difference φ 1 - φ 2 \u003d 0
Ohm's law for a closed chain can be written as
ε 12 \u003d IR + IR (13.17)
where IR and IR are a voltage drop according to the external and inner sections of the chain
The connection of sources in the battery can be sequential and parallel.
With a consecutive connection, two adjacent sources are connected by the collected poles.
With a serial connection of the EMF of the battery is equal to the amount of EDC of individual sources that make up the battery.
Current power in such a chain
(13.18)
If you combine all the positive and all negative poles of two or sources between yourself, then such a connection of energy sources is called parallel. In practice, sources are always connected in parallel with the same emf.
With a parallel connection of the same sources of electrical energy, the emf of the battery is equal to the EDC of one source.
Then according to the law of Ohm
(13.19)
Consider two limiting cases when the external resistance turns out to be either very large or, on the contrary, is negligible to small .
R.→ ∞ (orR. >> r.). Such a situation happens when the external chain is disconnected, i.e. When the pool of the current source is open and there is an air gap between them, through which the current does not go. Substituting into the generalized law of Oma i \u003d 0, we obtain φ 1 - φ 2 \u003d ε 12. This means that the voltage on the poles of the open source is equal to its EMF.
R.→ 0 (orR.<<r.). This situation is found with a short circuit. In this case, the current strength increases to magnitude
to 
laying may exceed the value allowable for this chain. A sharp increase in current with a short circuit may result in large heat release. The intensity of the field inside the battery disappears. Wires can melt or heat or become a cause of fire, the current source can fail. Fuses apply to avoid this.
Ohm's law for a homogeneous section of the chain (a plot not containing EDC) : the strength of the current in the conductor is directly proportional to the applied voltage and is inversely proportional to the resistance of the conductor.
Value
called electrical conductivity conductor . Conductivity unit - Siemens (cm).
The main law of electrical engineering, with which the electrical circuits can be studied and calculated is the law of Oma, which sets the ratio between the current, voltage and resistance. It is necessary to clearly understand its essence and be able to properly use it when solving practical tasks. Often errors are allowed in electrical engineering due to inability to properly apply the Ohm law.
Ohma law for a plot of chain says: The current is directly proportional to the voltage and inversely proportional to the resistance.
If you increase several times the voltage operating in the electrical circuit, then the current in this chain will increase in the same time. And if you increase the chain resistance several times, the current will decrease into the same time. Like this water flow in the pipe, the greater, the stronger the pressure and the smaller the resistance, which has a pipe movement pipe.
In a popular form, this law can be formulated as follows: the higher the voltage at one and the same resistance, the higher the current and at the same time the higher the resistance at the same voltage, the lower the current strength.
To express Ohm's law mathematically most simple, believe that the resistance of the conductor, in which the voltage of 1 V passes the current 1 A, is 1 Ohm.
Current in amperes can always be determined if split voltage in volts to resistance in Oma. therefore ohma law for a plot of chain written by the following formula:
I \u003d u / r.
Magic triangle
Any section or element of the electrical circuit can be described using three characteristics: current, voltage and resistance.
How to use the Ohm triangle: We close the desired value - the other two characters will give a formula to calculate it. By the way, the Ohm's law is called only one formula from the triangle - the one that reflects the dependence of the current from voltage and resistance. Two other formulas, although they are its consequence, do not have physical meaning.
Calculations performed using the Ohm law for the chain section will be correct in the case when the voltage is expressed in volts, resistance in Omah and current in amperes. If multiple units of measurements of these values \u200b\u200bare used (for example, milliamper, maglivolt, mega, etc.), they should be translated according to amps, volts and ohms. To emphasize this, sometimes the formula of the Ohm law for the section of the chain is written like this:
amp \u003d volt / ohm
You can also calculate the current in milliamperes and microampers, while the voltage must be expressed in volts, and resistance - in kiloma and megaoms, respectively.
Other articles about electricity in a simple and accessible presentation:
Ohm law is fair for any section of the chain. If it is required to determine the current in this section of the chain, then the voltage acting on this area is necessary (Fig. 1), divide the resistance of this particular area.
Figure 1. Application of the Ohm Law for the Chain Plot
We give an example of calculating the current by the law of Ohm. Let it be required to determine the current in a lamp having a resistance of 2.5 ohms if the voltage applied to the lamp is 5 V. separating 5 to 2.5 ohms, we obtain the value of the current equal to 2 A. in the second example, we define the current that will be Because of the voltage of 500 V in the chain, the resistance of which is 0.5 MΩ. To do this, express resistance in Omah. Dividing 500 V per 500 000 Ohm, we find the value of the current in the chain, which is equal to 0.001 A or 1 mA.
Often, knowing the current and resistance are determined by the Ohm law voltage. We write a formula to determine the voltage
U \u003d Ir.
From this formula it is clear that voltage at the ends of this section of the chain is directly proportional to the current and resistance. The meaning of this dependence is not difficult. If you do not change the resistance of the area of \u200b\u200bthe chain, then you can increase the current only by increasing the voltage. It means with constant resistance greater current corresponds to more voltage. If you need to get the same current at different resistances, then with a larger resistance there must be more voltage accordingly.
Voltage on the section of the chain is often called tension drop. This often leads to a misunderstanding. Many people think that the voltage drop is some kind of lost unnecessary tension. In reality, the stress and voltage drop is equivalent.
The voltage calculation using the Ohm law can be shown on the following example. Let a current of 5 mA passes through a plot of a chain with a resistance of 10 kΩ and it is required to determine the voltage in this area.
Multimily I \u003d 0.005 A on R -10000 Ohms, we obtain a voltage equal to 5 0 V. It would be possible to get the same result, multiplying 5 ma per 10 com: u \u003d 50 V
In electronic devices, the current is usually expressed in milliamperes, and resistance in kiloma. Therefore, it is convenient in the calculations according to the law of Ohm, it is these units of measurements.
According to the law of Ohm, resistance is also calculated if the voltage and current is known. The formula for this case is written as follows: R \u003d u / i.
Resistance always represents the voltage ratio to the current. If the voltage is increased or decreasing several times, the current will increase or decrease at the same number. The ratio of voltage to the current equal to the resistance remains unchanged.
It should not be understood as a formula for determining the resistance in the sense that the resistance of this conductor depends on the outflow and voltage. It is known that it depends on the length, cross-sectional area and material of the conductor. According to the appearance of the formula for determining the resistance, it resembles a formula for calculating the current, but there is a fundamental difference between them.
The current in this section of the chain really depends on the voltage and resistance and varies when they are changed. And the resistance of this section of the chain is a permanent value that does not depend on the change in voltage and current, but equal to the ratio of these quantities.
When the same current passes in two sections of the chain, and the voltages attached to them are different, it is clear that the site to which more voltage is applied is, it has more resistance.
And if under the action of the same voltage in two different sections of the chain there is a different current, then the smaller current will always be on the plot that has greater resistance. All this follows from the main wording of the Ohm law for the chain section, i.e. from the fact that the current is the greater, the greater the voltage and the less resistance.
The calculation of resistance using the Ohm law for the chain section will show the following example. Let it be necessary to find the resistance of the site through which at a voltage of 40 V current 50 mA. Expressing the current in amps, we obtain i \u003d 0.05 A. We divide 40 by 0.05 and we find that the resistance is 800 ohms.
Ohm's law can be clearly represented in the form of the so-called volt-ampere characteristics. As is known, a direct proportional dependence between two values \u200b\u200bis a straight line passing through the origin of the coordinates. This dependence is called linear.
In fig. 2 is shown as an example, the chart of the Ohm law for the chain area with a resistance of 100 ohms. Along the horizontal axis, the voltage is postponed, and along the vertical axis - the current in amperes. The scale of the current and voltage can be selected by how much. The straight line has been carried out so that for any of its point, the voltage ratio is equal to 100 ohms. For example, if u \u003d 50 V, then i \u003d 0.5 A and R \u003d 50: 0.5 \u003d 100 ohms.
Fig. 2. Ohm law (volt-ampere characteristic)
The schedule of the Ohm law for negative current and voltage values \u200b\u200bhas the same form. This suggests that the current in the chain passes the same in both directions. The more resistance, the smaller the current is obtained at this voltage and the more the hollow goes straight.
Instruments in which a volt-ampere characteristic is a straight line passing through the origin of the coordinate, that is, the resistance remains constant when the voltage or current is changed, called linear devices. Terminar chains, linear resistance are also used.
There are also devices in which resistance changes when voltage or current changes. Then the dependence between the current and voltage is not expressed according to the law of Ohm, but more difficult. For such devices, a volt-ampere characteristic will not be a straight line passing through the origin of the coordinates, and is either a curve or a broken line. These devices are called nonlinear.
Mnemonic chart for Ohm's Law
The magnitude of the impact, which the current can have on the conductor, be it a thermal, chemical or magnetic effect of the current. That is, adjusting the current strength, you can control it with exposure. Electric current, in turn, is an ordered movement of particles under the action of an electric field.
Dependence of current and voltage
Obviously, the stronger the field acts on the particles, the greater the power of the current in the chain. The electric field is characterized by a value called voltage. Therefore, we conclude that the current current depends on the voltage.
And indeed, the experimental way was able to establish that the current strength is associated with the voltage is directly proportional. In cases where the voltage value was changed in the circuit, without changing all other parameters, the current of the current increased or decreased to the same time, which voltage changed.
Communication with resistance
However, any chain or section of the chain is characterized by another important value of the electrical current resistance. Resistance is associated with the power of the current inversely proportional. If you change the amount of resistance to any section of the chain, without changing the voltage at the ends of this section, the current will also change. And if we reduce the amount of resistance, the current force will increase the same time. And, on the contrary, with an increase in resistance, the current strength is proportionally decreased.
Formula of the Ohm Law for Sign
By comparing two of these dependencies, you can come to the same conclusion that I came to the German scientist Georg Ohm in 1827. He tied up three of the above physical quantities and brought the law, which called him name. Ohma law for a plot of chain says:
The strength of the current in the section of the chain is directly proportional to the voltage at the ends of this section and is inversely proportional to its resistance.
where I is the current strength
U - Voltage,
R - resistance.
Application of the Law Ohm.
Ohm's law is one of fundamental laws of physics. Opening it at one time allowed to make a huge leap in science. Currently, it is impossible to imagine any very elemental calculation of the basic electrical values \u200b\u200bfor any chain without using the Ohm law. The idea of \u200b\u200bthis law is not a lot of electronics engineers exclusively, but the necessary part of the basic knowledge of any little of the educated person. No wonder there is a saying: "Do not know the law of Oma - Sidi at home."
U \u003d Ir. and R \u003d U / I
True, it should be understood that in the collected chain the amount of resistance of some section of the chain is the value constant, therefore, when the current change, only the voltage will change and vice versa. To change the resistance of the area of \u200b\u200bthe chain, the chain should be collected. The calculation of the required amount of resistance in designing and assembling the chain can be made according to the law of Ohm, based on the estimated values \u200b\u200bof the current and voltage force, which will be skipped through this section of the chain.
Ignorance of the law is not an excuse.
Aphorism
I wonder what laws will be discussed in the lesson at number three. Is it really in the electrical engineering of these laws a whole mountain or even a bunch and need to remember? Now we will find out. Hello, dear! Probably, many of you are already with annoyance in the eyes look at the next lesson and think about yourself: "What a scarlet!", And maybe you are even going to leave our slender rows? Do not rush, everything just begins! The initial stage is always boring ... from this lesson and will go all the most interesting. Today I will tell you who is in the electrother engine to whom a friend, and to whom and the enemy, what will happen if the e-fintle student wake in the middle of the night, and how with the help of one finger to understand half of all electrical engineering. Interesting? Then we went!
With the first our friend, we met on the past lesson - this is the power of the current. It characterizes electricity from the point of view of the charge rate of the charge from one point of space to another under the action of the field. But, as was noticed, the current strength depends on the properties of the conductor through which this current "runs". For current stream, the value of the specific electrical conductivity of the material is directly affected. Now imagine a certain conductor (suitable such as in Figure 3) with electron moving in it. The main disadvantage of the electron I would call the absence of a steering wheel. Because of this, the lack of electron movement is determined only by the field effect on them and the structure of the material in which they are moving.
Since the electrons "do not know how to turn", some of them may face the crystalline grille with the circles, losing their speed from the collision, and thereby reduce the rate of charge transfer, that is, lower the current strength. Some electrons may lose so much energy, which "stick" to the ion and turn it into a neutral atom. Now, if we increase the length of the conductor, it is obvious that the number of such collisions will also increase, and the electrons will give even more energy, that is, the current will decrease. But with an increase in the cross-sectional area of \u200b\u200bthe conductor, only the number of free electrons increases, and the number of collisions per unit area almost does not change, therefore the current increases with the increasing area. So, we found out that the electrical conductivity (it has already become not specific, as it takes into account the geometric sizes of a particular conductor) depends on the three characteristics of the conductor: the lengths, cross-sectional area and material.
However, the better the material carries out the electric current, the less he "resists" its passage. These statements are equivalent. It's time to get acquainted with our second friend - electrical resistance. This is the value, the inverse amount of conductivity and depends on the same characteristics of the conductor.
Figure 3.1 - From what depends the resistance of the conductor
In order to take into account with the numerical calculation of the influence of the genus on its electrical resistance, the value of the specific electrical resistance is introduced, which characterizes the ability of the substance to carry out an electric current. Note that the determination of electrical conductivity and electrical resistance is identical, as well as approval above. The resistivity is defined as the resistance of the conductor with a length of 1M and cross-section of 1M 2. It is indicated by the Latin letter ρ ("RO") and has the dimension of OM M. Ohm - a unit of measurement of resistance, which is the reverse magnitude of Siemens. Also, MM 2 / m dimension can be used to determine the specific resistance, which is a million times smaller than the main dimension.
Thus, the electrical resistance of the conductor can be described through its geometric and physical properties as follows: 
where ρ is the specific electrical resistance of the conductor material;
L - Explorer length;
S is the cross-sectional area of \u200b\u200bthe conductor.
The dependence is evidenced that the resistance of the conductor increases with increasing the length of the conductor and decreases with an increase in the cross-sectional area, as well as directly depends on the values \u200b\u200bof the specific resistance of the material.
And now we remember that the magnitude of the current strength in the conductor affects the tension of the electric field, under the action of which an electric current occurs. Oh, how many millions of thousand times it has already been mentioned that the electric current occurs under the action of the electric field! This fact should always be kept in the head. There are, of course, and other ways to create a current, but so far we will consider only this. As mentioned above, an increase in the field strength leads to an increase in current, and quite recently we found out that the more energy will save the electron when driving through the conductor, the higher the electrical current value. From the course of mechanics it is known that the energy of the body is determined by its kinetic and potential energy. So, the point charge placed in the electric field has only potential energy in the initial moment (since its speed is zero). For the characteristics of this potential energy of the field, which the value of the electrostatic potential is introduced, equal to the ratio of potential energy to the size of the point charge: 
where W p is a potential energy
Q is a point charge.
After the charge falls under the action of the electric field, it will start moving at a certain speed and part of its potential energy will switch to kinetic. Thus, at two points of the field, the charge will have a different value of potential energy, that is, two points of the field can be characterized by different potential values. The potential difference is defined as the ratio of changes in potential energy (perfect field work) to the size of a point charge: 
Moreover, the operation of the field does not depend on the path of the charge and characterizes only the magnitude of the potential energy change. The potential difference is also called electrical voltage. The voltage is made to denote the English letter U ("y"), the unit of measurement of the voltage is the value volt (B), named after Italian physics and physiologist Alessandro Volta, who invented the first electrical battery.
Well, we got acquainted with three inseparable friends in electrical engineering: amp, volts and ohm or current, voltage and resistance. Any component of the electrical circuit can be unambiguously characterized using these three electrical characteristics. The first who became acquainted and made friends with all three immediately was George Ohm, which discovered that the tension, current and resistance are connected with each other with a certain ratio:
which was subsequently called the law of Ohm.
The power of the electric current in the conductor is directly proportional to the voltage at the ends of the conductor and is inversely proportional to the resistance of the conductor.
This wording needs to know from the title letter C to the point at the end. It is rumored that the first phrase of any admirer student, awakened among the night, will be the wording of the law of Ohm. This is one of the basic laws of electrical engineering. This formulation is called integral. In addition, it also has a differential formulation, reflecting the dependence of the current density from the characteristics of the field and the material of the conductor:
where σ is the specific conductivity of the conductor,
E - electric field strength.
This formulation follows from the formula given in the second lesson, and differs from the integral because it does not take into account the geometric characteristics of the conductor, taking into account only its physical characteristics. This formulation is interesting only from the point of view of theory and in practice it does not apply.
To quickly memorize and use the Ohm law, you can apply the diagram shown in the figure below. 
Figure 3.2 - "Triangular" Law Ohm
The rule of use of the chart is simple: it is enough to close the desired value and the other two symbols will give the formula to calculate it. For example. 
Figure 3.3 - How to Remember Ohm
With a triangle we finished. It is worth adding that the Ohm's law is only one of the above formulas, which reflects the dependence of the current from voltage and resistance. Two other formulas, although they are its consequence, do not have physical meaning. So do not confuse!
A good interpretation of the Ohm law is a drawing that most clearly reflects the essence of this law: 
Figure 3.4 - Ohm's law clearly
As we can see, in this figure are the three of our new friends: ohm, amp and volts. Volt is trying to push the amp through the conductor cross section (the current is directly proportional to the voltage), and then, on the contrary, interferes with this (and inversely proportional to the resistance). And the stronger I "tighten" the conductor, the harder the amper will crawl. But if the volt is sleeping row ...
It remains to figure out why the term "many laws" appears in the name of the lesson, because we have one's law - Ohm's law. Well, firstly, there are two wording for him, secondly, we have learned only the so-called Ohma law for a circuit site, and there is another Ohma law for a complete chain that we will look at the next lesson, thirdly, we have At least two consequences of the Ohm's law, allowing to find the value of the resistance of the circuit site and the voltage in this area. So the law is only one, but it can be used in different ways.
Finally, I will tell another interesting fact. 10 years after the appearance of the "Ohm Law" appeared, one French physicist (and in France, Ohm has not yet been known) on the basis of experiments came to the same conclusions. But he was stated that the law established by him in 1827. It was opened by Ohom. It turns out that French schoolchildren and today study the law of Ohm under a different name - for them this is the law of the pool. That's how. On this regular lesson is completed. To new meetings!
- Any plot or element of the electrical circuit can be unambiguously characterized using three characteristics: current, voltage and resistance.
- Resistance (R) - Characteristics of the conductor reflecting the degree of its electrical conductivity and depending on the geometric size of the conductor and the genus of the material from which it is manufactured.
- Voltage (U) - the same as the potential difference; The value is equal to the attitude of the electric field to move the point charge from one point of space to another.
- The current, voltage and resistance are related to the ratio I \u003d U / R, called the Ohm's law (the power of the electric current in the conductor is directly proportional to the voltage at the ends of the conductor and is inversely proportional to the conductor resistance).
As well as tasks:
- If the wire length is pulling to increase twice, then how will its resistance change?
- What conductor is greater resistance: copper solid rod or copper tube having an outer diameter equal to the diameter of the rod?
- The difference of potentials at the ends of the aluminum conductor is equal to 10V. Determine the density of the current flowing through the conductor if its length is 3m.
