The leads of the coil of copper wire are connected to a sensitive galvanometer. In which of the experiments listed below will the galvanometer indicate the flow
Guys, I won’t pass these tasks, the only 3 will come out! Help) 1. What is the resistance of 1 m of constantan wire with a diameter of 0.8 mm? 2.Whenwinding a coil of copper wire, its mass increased by 17.8 d,a resistance turned out to be 34 Ohm. Estimate the length and cross-sectional area of \u200b\u200bthe wire from these data?
3. An ammeter and a resistor with a resistance of 2 ohms were connected in series to a current source with an internal resistance of 1 ohm. At the same time, the ammeter showed 1 A. What will the ammeter show if a 3 ohm resistor is used?
4. In the circuit, the voltmeter shows 3V, and the ammeter 0.5 A. With a current of 1A, the voltmeter shows 2.5 V. What are the EMF and internal resistance of the source?
5. A force of 6N acts on a charge of 3C in an electrostatic field. What is the field strength?
a.18 n/k b.0.5 n/k c.2n/k d 24 n/k e.there are no correct answers
6. How will the strength of the electric field of a point charge transferred from vacuum to a medium with a dielectric constant equal to 81 change?
a. will increase by 9 times b. will decrease by 9 times c. will increase in 81 d. will decrease by 81 times e. will not change
10. When moving an electric charge between points with a potential difference of 8 V, the forces acting on the charge from the electric field did the work of 4 J. What is the magnitude of the charge?
a.4 class b.32 class c.0.5 class d.2 class e.no correct
11. Charge 2cl moves from a point with a potential of 10 V to a point with a potential of 15 V. What work does the electric field do in this case?
a.10 j b.-10 j c.0.4 j d.2.5 j e. no correct
12. When a charge of 3 cells moves from 1 point to another, the electric field does 6 J of work. What is the potential difference between these points?
a.18 C b.2C c.0.5C d.9 E. no correct
13. How will the capacitance of a capacitor change when a dielectric with a permittivity of 2 is removed from it?
1) Determine the resistance of the heating element of the electric furnace, made of constantan wire with a cross-sectional area of 1 mm insquare and 24.2m long. 2) The 20 m extension cable is made of copper wire with a diameter of 1.2 mm. What is the resistance of the extension cord? What is the voltage drop across it if a current of 10 A flows through it?
1) Determine the resistance of the heating element of the electric furnace, made of constantan wire with a cross-sectional area of 1mm2 andlength 24.2m
2) 20 m long extension cable made of copper wire with a diameter of 1.2 mm. What is the resistance of the extension cord? what is the voltage drop across it if a current of 10A flows through it
Electrical wiring is made of copper wire 200 m long and 10 mm^2 in cross section. What is its resistance? What section should be chosenMore than half a century of evolution of carburetor gasoline engines with a contact ignition system, the coil (or, as drivers of past years often called it, a “reel”) practically did not change its design and appearance, representing a high-voltage transformer in a metal sealed glass filled with transformer oil to improve insulation between winding turns and cooling.
An integral partner of the coil was a distributor - a low voltage mechanical switch and a high voltage distributor. The spark should have appeared in the respective cylinders at the end of the compression stroke of the air-fuel mixture - strictly at a certain moment. The distributor carried out both the generation of a spark, and its synchronization with the cycles of the engine, and distribution by candles.
The classic oil-filled ignition coil - "reel" (which in French meant "coil") - was extremely reliable. From mechanical influences it was protected by a steel glass of the case, from overheating - an effective heat sink through the oil filling the glass. However, according to the little-censored rhyme in the original version, “It was not about the reel - the idiot was sitting in the cab ...”, it turns out that a reliable reel sometimes failed, even if the driver was not such an idiot ...
If you look at the diagram of the contact ignition system, you can find that the muffled engine could stop in any position of the crankshaft, as with closed contacts low voltage breaker in the distributor, and open. If, during the previous shutdown, the engine stopped in the crankshaft position, in which the distributor cam closed the contacts of the breaker that supplied low voltage to the primary winding of the ignition coil, then when the driver, for some reason, turned on the ignition without starting the engine, and left the key in this position for a long time, the primary winding of the coil could overheat and burn out ... For a direct current of 8-10 amperes began to pass through it instead of an intermittent pulse.
Officially, the coil of the classic oil-filled type is not repairable: after the winding burned out, it was sent to the scrap. However, once upon a time at car depots, electricians managed to repair reels - they flared the case, drained the oil, rewound the windings and reassembled ... Yes, there were times!
And only after the mass introduction of contactless ignition, in which the distributor contacts were replaced by electronic switches, the problem of coil combustion almost disappeared. Most switches have automatic shutdown current through the ignition coil with the ignition on, but the engine not running. In other words, after the ignition was turned on, a small time interval began to count down, and if the driver did not start the engine during this time, the switch automatically turned off, protecting both the coil and itself from overheating.
dry coils
The next stage in the development of the classic ignition coil was the rejection of the oil-filled housing. "Wet" coils were replaced by "dry". Structurally, it was practically the same coil, but without metal case and oils, covered with a layer of epoxy compound on top to protect against dust and moisture. She worked in conjunction with the same distributor, and often on sale one could find both old “wet” coils and new “dry” coils for the same car model. They were completely interchangeable, even the “ears” of the mounts matched.
For the average car owner, there were essentially no advantages or disadvantages in changing the technology from wet to dry. If the latter, of course, was made with high quality. "Profit" was received only by manufacturers, since it is somewhat easier and cheaper to make a "dry" coil. However, if the "dry" coils of foreign car manufacturers were initially thought out and manufactured quite carefully and served almost as long as the "wet" ones, the Soviet and Russian "dry" coils gained notoriety, because they had a lot of quality problems and failed quite often without any reason.
One way or another, today “wet” ignition coils have completely given way to “dry”, and the quality of the latter, even of domestic production, is practically not satisfactory.
There were also hybrid coils: an ordinary “dry” coil and a conventional contactless ignition switch were sometimes combined into a single module. Such designs were found, for example, on single-injection Fords, Audis and a number of others. On the one hand, it looked to some extent technologically advanced, on the other hand, reliability decreased and the price increased. After all, two fairly heating nodes were combined into one, while individually they cooled better, and if one or another failed, the replacement was cheaper ...
Oh yes, even in the piggy bank of specific hybrids: on old Toyotas, there was often a variant of a coil integrated directly into the distributor of the distributor! It was integrated, of course, not tightly, and in the event of a failure, the “reel” could be easily removed and purchased separately.
Ignition module - failure of the distributor
A noticeable evolution in the coil world occurred during the development of injection motors. The first injectors included a “partial distributor” - the low-voltage circuit of the coil was already switched by the electronic engine control unit, but the classic runner distributor, driven by the camshaft, was still distributing the spark through the cylinders. It became possible to completely abandon this mechanical unit by using a combined coil, in the common body of which individual coils were hidden in an amount corresponding to the number of cylinders. Such nodes began to be called "ignition modules".
The electronic engine control unit (ECU) contained 4 transistor switches, which alternately applied 12 volts to primary windings all four coils of the ignition module, and they in turn sent a spark pulse high voltage each for its own candle. Simplified versions of combined coils are even more common, more technologically advanced and cheaper to manufacture. In them, in one housing of the ignition module of a four-cylinder engine, not four coils are placed, but two, but working, nevertheless, for four candles. In such a scheme, a spark is supplied to the candles in pairs - that is, it comes to one candle from a pair at the moment necessary to ignite the mixture, and to the other - idle, at the moment the exhaust gases are released from this cylinder.
The next stage in the development of combined coils was the transfer of electronic switching keys (transistors) from the engine control unit to the ignition module housing. The removal of powerful and heating transistors “to the wild” improved the temperature regime of the computer, and if any electronic switch-key failed, it was enough to replace the coil, and not change or solder the complex and expensive control unit. In which immobilizer passwords, individual for each car, and similar information are often registered.
Each cylinder - on the coil!
Another typical ignition solution for modern gasoline cars, which exists in parallel with modular coils, is individual coils for each cylinder, which are installed in the spark plug well and contact the spark plug directly, without a high-voltage wire.
The first "personal coils" were just coils, but then switching electronics moved into them - just as it happened with ignition modules. Of the advantages of this form factor is the rejection of high-voltage wires, as well as the ability to replace only one coil, rather than the entire module, if it fails.
True, it is worth saying that in this format (coils without high-voltage wires mounted on a candle) there are also coils in the form of a single block, united by a common base. Such, for example, like to use GM and PSA. This is truly a nightmare technical solution: the coils seem to be separate, but if one “bobbin” fails, you have to change the assembly of a large and very expensive unit ...
What have we come to?
The classic oil-filled bobbin was one of the most reliable and indestructible units in carbureted and early injection cars. Sudden failure of it was considered a rarity. True, its reliability, unfortunately, was "compensated" by an integral partner - a distributor, and later - an electronic switch (the latter, however, only applied to domestic products). The “dry” coils that replaced the “oil” coils were comparable in terms of reliability, but still failed somewhat more often for no apparent reason.
Injection evolution forced to get rid of the distributor. This is how various designs appeared that did not need a mechanical high-voltage distributor - modules and individual coils according to the number of cylinders. The reliability of such structures has decreased even more due to the complication and miniaturization of their "offal", as well as the extremely difficult conditions of their work. After several years of operation with constant heating from the engine on which the coils were mounted, cracks formed on the protective layer of the compound, through which moisture and oil entered the high-voltage winding, causing breakdowns inside the windings and misfiring. With individual coils that are installed in candle wells, working conditions are even more hellish. Also, gentle modern coils do not like washing the engine compartment and the increased gap in the electrodes of the spark plugs, which is formed as a result of the long-term operation of the latter. The spark is always looking for the shortest path, and often finds it inside the winding of the bobbin.
As a result, today the most reliable and correct design of the existing and used ones can be called an ignition module with built-in switching electronics, mounted on an engine with an air gap and connected to spark plugs by high-voltage wires. Less reliable are separate coils installed in the candle wells of the head of the block, and, from my point of view, the solution in the form of combined coils on a single ramp is completely unsuccessful.
Option I
1. Who discovered the phenomenon of electromagnetic induction?
a) X. Oersted; b) Sh. Coulomb;
c) A. Volta; d) A. Ampère;
e) M. Faraday; f) D. Maxwell.
2. Coil leads of copper wire are connected to a sensitive
EMF of electromagnetic induction in the coil?
a permanent magnet is inserted into the coil;
a permanent magnet is removed from the coil;
the permanent magnet rotates around its longitudinal axis inside the coil.
a) only in case 1; b) only in case 2;
c) only in case 3; d) in cases 1 and 2;
e) in cases 1, 2 and 3.
3. What is the name of the physical quantity equal to the product of the moduleAT
magnetic field induction per areaSsurface penetrated by the magnetic
filament field, and the cosine of the angleα
between vectorATinduction and normal
nto this surface?
a) inductance; b) magnetic flux;
c) magnetic induction; d) self-induction;
e) magnetic field energy.
4. What is the name of the unit of measurement of magnetic flux?
a) Tesla; b) weber;
5. At points 1. 2. 3 the location of the magnetic arrows is shown (Fig. 68) Draw how the magnetic induction vector d) henry is directed at these points. Points 1, 2, 3 show the location of the magnetic needles (Fig. 68). Draw how the magnetic induction vector is directed at these points.
6Lines of magnetic field inductions go from left to right parallel to the plane of the sheet, the conductor with current is perpendicular to the plane of the sheet, and the current is directed to the plane of the notebook. The vector of the Ampere force acting on the conductor is directed ...
a) to the right; b) to the left;
c) up; d) down.
Option II
1. What is the name of the phenomenon of occurrence electric current in the closed
that circuit when changing the magnetic flux through the circuit?
a) electrostatic induction; b) the phenomenon of magnetization;
c) Ampere force; d) Lorentz force;
e) electrolysis; f) electromagnetic induction.
2.
The conclusions of the coil of copper wire are attached to the sensitive
galvanometer. In which of the following experiments will the galvanometer detect
the occurrence of EMF of electromagnetic induction in the coil?
a permanent magnet is inserted into the coil;
the coil is put on a magnet;
the coil revolves around a magnet inside it.
a) in cases 1, 2 and 3; b) in cases 1 and 2;
c) only in case 1; d) only in case 2;
e) only in case 3.
3. Which of the following expressions determines the magnetic flux?
a) BS cosα b) ∆F/∆t
B) qVBsinα; d) qVBI;
e) IBl sin α .
4. The unit of change of what physical quantity is 1 weber?
a) magnetic field induction; b) electrical capacity;
c) self-induction; d) magnetic flux;
e) inductance.
5. Draw a picture of the lines of magnetic induction at
the flow of current through the coil (Fig. 69), wound on
cardboard cylinder. How will this picture change when:
a) increasing the current in the coil?
b) a decrease in the number of turns wound on a coil?
c) into the introduction of an iron core into it?
6. Conductor with current lies in the plane of the sheet. A current flows through the conductor from below, and the Ampere force directed from the sheet acts upward on it. This can happen if the north pole of a bar magnet is brought up...
a) on the left b) on the right;
c) from the front side of the sheet; d) on the reverse side of the sheet.
The standard design of an inductor consists of an insulated wire with one or more strands wound in a spiral around a dielectric frame, having a rectangular, cylindrical or shape. Sometimes, coil designs are frameless. The wire is wound in one or more layers.
In order to increase the inductance, ferromagnet cores are used. They also allow you to change the inductance within certain limits. Not everyone fully understands why an inductor is needed. It is used in electrical circuits as a good conductor. direct current. However, when self-induction occurs, resistance arises that prevents the passage of alternating current.
Varieties of inductors
There are several design options for inductors, the properties of which determine the scope of their use. For example, the use of loop inductors together with capacitors makes it possible to obtain resonant circuits. They are characterized by high stability, quality and precision.
Coupling coils provide inductive coupling of individual circuits and cascades. Thus, it becomes possible to divide the base and circuits in direct current. High precision is not required here, therefore, thin wire is used for these coils, wound in two small windings. The parameters of these devices are determined in accordance with the inductance and coupling coefficient.
Some coils are used as variometers. During operation, their inductance can change, which allows you to successfully rebuild oscillatory circuits. The whole device includes two coils connected in series. The moving coil rotates inside the fixed coil, thereby creating a change in inductance. In fact, they are a stator and a rotor. If their position changes, then the value of self-induction will also change. As a result, the inductance of the device can change by 4-5 times.
In the form of chokes, those devices are used that have high resistance with alternating current, and very low resistance with direct current. Due to this property, they are used in radio engineering devices as filter elements. At a frequency of 50-60 hertz, transformer steel is used to make their cores. If the frequency is higher, then the cores are made of ferrite or permalloy. Separate varieties of chokes can be observed in the form of so-called barrels that suppress interference on wires.
Where are inductors used?
The scope of each such device is closely related to the features of its design. Therefore, it is necessary to take into account its individual properties and technical characteristics.
Together with resistors or, the coils are involved in various circuits that have frequency-dependent properties. First of all, these are filters, oscillatory circuits, circuits feedback And so on. All types of these devices contribute to the accumulation of energy, the conversion of voltage levels in a switching regulator.
When two or more coils are inductively coupled together, a transformer is formed. These devices can be used as electromagnets, as well as an energy source that excites an inductively coupled plasma.
Inductive coils are successfully used in radio engineering, as a transmitter and receiver in annular structures and those working with electromagnetic waves.
I welcome everyone to our site!
We continue to study electronics from the very beginning, that is, from the very basics and the topic of today's article will be principle of operation and main characteristics of inductors. Looking ahead, I will say that first we will discuss the theoretical aspects, and we will devote several future articles entirely to the consideration of various electrical circuits, which use inductors, as well as elements that we studied earlier in our course - and.
The device and principle of operation of the inductor.
As is already clear from the name of the element - the inductor, first of all, is just a coil :), that is a large number of turns of insulated conductor. Moreover, the presence of insulation is the most important condition - the turns of the coil should not close with each other. Most often, the turns are wound on a cylindrical or toroidal frame:
The most important characteristic inductors is, of course, inductance, otherwise why would it be given such a name 🙂 Inductance is the ability to convert the energy of an electric field into the energy of a magnetic field. This property of the coil is due to the fact that when current flows through the conductor, a magnetic field arises around it:
And here is what the magnetic field that occurs when current passes through the coil looks like:
In general, strictly speaking, any element in electrical circuit has inductance, even an ordinary piece of wire. But the fact is that the value of such an inductance is very small, in contrast to the inductance of the coils. Actually, in order to characterize this value, the Henry unit (H) is used. 1 Henry is actually a very large value, so the most commonly used are µH (microhenry) and mH (milihenry). the value inductance coils can be calculated using the following formula:
Let's see what the value is included in this expression:
It follows from the formula that with an increase in the number of turns or, for example, the diameter (and, accordingly, the cross-sectional area) of the coil, the inductance will increase. And as the length increases, it decreases. Thus, the turns on the coil should be placed as close as possible to each other, as this will reduce the length of the coil.
FROM inductor device we figured it out, it's time to consider the physical processes that occur in this element when an electric current passes. To do this, we will consider two circuits - in one we will pass a direct current through the coil, and in the other - an alternating current 🙂
So, first of all, let's figure out what happens in the coil itself when current flows. If the current does not change its magnitude, then the coil has no effect on it. Does this mean that in the case of direct current, the use of inductors is not worth considering? But no 🙂 After all, direct current can be turned on / off, and just at the moments of switching, all the most interesting happens. Let's take a look at the chain:
In this case, the resistor plays the role of a load, in its place could be, for example, a lamp. In addition to the resistor and inductance, the circuit includes a constant current source and a switch, with which we will close and open the circuit.
What happens when we close the switch?
Current through the coil will begin to change, since at the previous time it was equal to 0. A change in current will lead to a change in the magnetic flux inside the coil, which, in turn, will cause an emf ( electromotive force) self-induction, which can be expressed as follows:
The occurrence of EMF will lead to the appearance of an induction current in the coil, which will flow in the direction, opposite direction power supply current. Thus, the self-induction EMF will prevent the current from flowing through the coil (the inductive current will cancel the circuit current due to their opposite directions). And this means that at the initial moment of time (immediately after the switch is closed), the current through the coil will be equal to 0. At this moment of time, the self-induction EMF is maximum. And what will happen next? Since the magnitude of the EMF is directly proportional to the rate of change of the current, it will gradually weaken, and the current, respectively, on the contrary, will increase. Let's look at graphs illustrating what we have discussed:
On the first graph we see circuit input voltage- initially the circuit is open, and when the switch is closed, constant value. In the second graph, we see change in the amount of current through the coil inductance. Immediately after the key is closed, the current is absent due to the occurrence of self-induction EMF, and then it begins to increase smoothly. The voltage on the coil, on the contrary, at the initial moment of time is maximum, and then decreases. The voltage graph on the load will coincide in shape (but not in magnitude) with the graph of the current through the coil (since in a series connection, the current flowing through different elements of the circuit is the same). Thus, if we use a lamp as a load, then they will not light up immediately after the switch is closed, but with a slight delay (in accordance with the current graph).
A similar transient process in the circuit will also be observed when the key is opened. An EMF of self-induction will appear in the inductor, but the inductive current in the event of an opening will be directed in the same direction as the current in the circuit, and not in the opposite direction, so the stored energy of the inductor will go to maintain the current in the circuit:
After opening the key, an EMF of self-induction occurs, which prevents the current from decreasing through the coil, so the current reaches zero value not immediately, but after some time. The voltage in the coil is identical in form to the case of closing the switch, but opposite in sign. This is due to the fact that the change in current, and, accordingly, the EMF of self-induction in the first and second cases are opposite in sign (in the first case, the current increases, and in the second it decreases).
By the way, I mentioned that the value of the EMF of self-induction is directly proportional to the rate of change in the current strength, and so, the proportionality factor is nothing more than the inductance of the coil:
This concludes with inductors in DC circuits and moves on to AC circuits.
Consider a circuit in which an alternating current is applied to the inductor:
Let's look at the dependences of the current and EMF of self-induction on time, and then we'll figure out why they look like this:
As we have already found out EMF self-induction we have directly proportional and opposite in sign to the rate of change of current:
Actually, the graph demonstrates this dependence to us 🙂 See for yourself - between points 1 and 2, the current changes, and the closer to point 2, the less changes, and at point 2, for some short period of time, the current does not change at all its meaning. Accordingly, the rate of current change is maximum at point 1 and gradually decreases when approaching point 2, and at point 2 it is equal to 0, which we see on EMF diagram of self-induction. Moreover, on the entire interval 1-2, the current increases, which means that the rate of its change is positive, in connection with this, on the EMF, on the whole this interval, on the contrary, it takes negative values.
Similarly, between points 2 and 3 - the current decreases - the rate of current change is negative and increases - the self-induction EMF increases and is positive. I won’t describe the rest of the graph – all processes follow the same principle there 🙂
In addition, a very important point can be seen on the graph - with an increase in current (sections 1-2 and 3-4), the self-induction EMF and current have different signs (section 1-2: , title="(!LANG:Rendered by QuickLaTeX.com" height="12" width="39" style="vertical-align: 0px;">, участок 3-4: title="Rendered by QuickLaTeX.com" height="12" width="41" style="vertical-align: 0px;">, ). Таким образом, ЭДС самоиндукции препятствует возрастанию тока (индукционные токи направлены “навстречу” току источника). А на участках 2-3 и 4-5 все наоборот – ток убывает, а ЭДС препятствует убыванию тока (поскольку индукционные токи будут направлены в ту же сторону, что и ток источника и будут частично компенсировать уменьшение тока). И в итоге мы приходим к очень !} interesting fact- The inductor resists the alternating current flowing through the circuit. So it has resistance, which is called inductive or reactive and is calculated as follows:
Where is the circular frequency: . - this is .
Thus, the higher the frequency of the current, the more resistance the inductor will provide to it. And if the current is constant (= 0), then the reactance of the coil is 0, respectively, it does not affect the flowing current.
Let's go back to our graphs that we built for the case of using an inductor in an AC circuit. We have determined the EMF of the self-induction of the coil, but what will be the voltage? Everything is really simple here 🙂 According to the 2nd Kirchhoff law:
And consequently:
Let's build on one graph the dependences of current and voltage in the circuit on time:
As you can see, current and voltage are phase-shifted () relative to each other, and this is one of the most important properties of AC circuits that use an inductor:
When an inductor is connected to an alternating current circuit, a phase shift appears in the circuit between voltage and current, while the current lags behind the voltage by a quarter of the period.
So we figured out the inclusion of the coil in the AC circuit 🙂
On this, perhaps, we will finish today's article, it turned out to be quite voluminous, so we will talk further about inductors next time. So see you soon, we will be glad to see you on our website!
