Subject: Capacitors. The main types of capacitors

A capacitor is a device made up of two or more conductive plates separated from each other by dielectric conductors such as glass, plastic or mica, which are used to store an electrical charge.

Providing smooth current flow, coupling, decoupling, filtering and noise reduction are just some of the many uses of capacitors in electrical circuit design.

Without capacitors, there would be no modern electronic systems. For these and other reasons, you can often see the ad "buy capacitors" or "buy electrolytic capacitors."

You can buy any radio components in Tambov and other regions of the country without problems, and you can also carry out the necessary dismantling of electrical equipment in which there are breakdowns associated with microcircuits, boards, including the replacement of capacitors.

Capacitors are various kinds Let's take a look at the main ones.

Ceramic Capacitor

Ceramic capacitors are made from a ceramic material, barium and titanic acid, as the dielectric. The ceramic capacitor is not shaped like a coil and is best suited for applications where high frequencies are encountered.

Ceramic capacitors have good thermal stability, mechanical integrity, making them ideal for surface mounting. The absence of a self-healing mechanism and a significant aging rate are the main disadvantages of this type of capacitor.

electrolytic capacitor

An electrolytic capacitor has a conductive electrolyte layer between the dielectric and one electrode. Such capacitors have a high capacitance per unit volume and have polarity, therefore, must be included in circuits with respect to polarity. The operating frequency of electrolytic capacitors is limited to about 100 kHz.

Polymer film capacitor

Polymer film capacitors come in various types such as polyester, polypropylene, polystyrene, Teflon, and metallized plastic. These capacitors are called polymer film capacitors because they are made using plastic as a dielectric.

Such capacitors are durable and have well-balanced electrochemical properties. The disadvantage of polymer capacitors is that they have a low dielectric constant, which is offset by their good breakdown voltage. While a polymer film capacitor can be used for surface mounting, some of these capacitors cannot withstand soldering.

mica capacitor

In a mica capacitor, mica is used as the dielectric. Also, this capacitor has a thin silver plate. Such capacitors are useful for resonant circuits, frequency filters, and RF oscillators with low temperature coefficient and high RF performance. Mica capacitors are more expensive and more modern.

tantalum capacitor

The tantalum capacitor uses tantalum pentoxide as the dielectric and uses tantalum for the electrodes. This kind of capacitor is superior to the electrolytic capacitor due to its high capacitance and lack of current noise, making it ideal for similar circuits as the electrolytic capacitor. The tantalum capacitor has polarity and is sensitive to voltage inconsistency, and also does not tolerate the maximum rated operating voltage.

Other types of capacitors

There are also other types of capacitors with other dielectric materials such as glass, silicon dioxide, sapphire, gas, and so on. The properties of these capacitors vary depending on the materials used and can be used in modern devices such as microwave capacitors.

Appendix 4

Related message: CAPACITORS

A capacitor (from the Latin words "condenso" - I condense) is called two devices of different purposes; one of them is used in heat engineering, the other - in electrical engineering and radio engineering.

In heat engineering, for example, in steam engines, a condenser is a vessel cooled by water. Steam accumulates in it, which, when cooled, turns into water. In refrigerators, condenser tubes "condense" vapors ammonia, freon or other coolant.

An electric capacitor is a system of two or more electrodes (plates) separated by a dielectric, the thickness of which is small compared to the dimensions of the plates; such a system of electrodes has a mutual capacitance. An electric capacitor in the form of a finished product is used in electrical circuits where a concentrated capacitance is needed. The dielectric in them are gases, liquids, solid electrical insulating substances, as well as semiconductors. The plates of electric capacitors with gaseous and liquid capacitors are a system of metal plates with a constant gap between them. In k. e. with a solid dielectric, the plates are made of thin metal foil or metal layers are deposited directly on the dielectric. For some types of c.e. a thin dielectric layer is applied to the surface of the metal foil (1st plate), the 2nd plate is a metal or semiconductor film deposited on the dielectric layer on the other side, or an electrolyte into which the oxidized foil is immersed. In integrated circuits, 2 fundamentally new capacitors are used: diffusion and metal-oxide-semiconductor (M.O.P.). Diffusion capacitors use the capacitance of a p-n junction created by diffusion, which depends on the applied voltage. In k. e. type M.O.P. as dielectrics, a layer of silicon dioxide grown on the surface of a silicon wafer is used. The plates are a substrate with a low resistivity (silicon) and a thin aluminum film.

When a capacitor is charged, charges appear on its plates that are equal in value but opposite in sign. The potential difference between the plates varies in proportion to the charge. According to their shape, capacitors are distinguished:

1. flat, their electrical capacity

where C is the microcapacity of the capacitor,

ε is the dielectric constant of the medium between the capacitor plates,

ε0 - electrical constant,

S is the area of the capacitor lining,

d is the distance between the capacitor plates.

2. cylindrical, their capacity

where R and r are the radii between the coaxial cylinders,

L is the length of the generatrix of the cylinders.

3. spherical, their electrical capacity

where R and r are the radii of the sphere.

K. e. With gaseousdielectric(air, gas-filled and vacuum) have very small values of tg σ and any stability of the capacitance. Air k.e. constant capacity is used in measuring technology mainly as exemplary K. e. Air k.e. it is recommended to apply at U not higher than 1000 V. In el. high voltage circuits (over 1000 V) use gas-filled ( nitrogen, freon, etc.) and vacuum k.e. Vacuum k.e. have lower losses and are more resistant to vibrations than gas-filled ones. The value of the breakdown voltage of vacuum k. e. does not depend on atm. pressure, so they are widely used in aviation equipment. The main disadvantage of c.e. with a gas-filled electrician - a very low specific capacitance.

K. e. with a liquid dielectric have the same dimensions as the c.e. with a gaseous dielectric, a large capacitance, since the dielectric constant of liquids is higher than that of gases, however, such k. e. have a large TKE and large dielectric losses. For these reasons, they are not promising.

To k. e. with a solid inorganic dielectric include glass, glass-enamel and glass-ceramic, ceramic (low / high frequency) and mica. K. e. glass, glass-enamel and glass-ceramic are a multilayer package consisting of alternating layers of dielectric and plates (made of silver and other metals). Capacitor glass, low/high frequency glass enamel and glass ceramics are used as dielectric. These k.e. have relatively low losses, low TKE, resistant to humidity and temperature, have a large insulation resistance. The durability of these c.e. at normal voltage and maximum operating temperature of at least 500 h. Ceramic k. e. are a polycrystalline ceramic dielectric, on which plates (aluminum, platinum and palladium) are baked in. Leads are soldered to the plates and the entire structure is covered with a moisture-proof layer. Ceramic k.e. subdivided into low-voltage high-frequency (low losses, high resonant frequency, small dimensions and weight), low-voltage low-frequency (increased specific capacitance, relatively large losses) and high-voltage k. e. (up to 30 square meters), which use special. ceramics with high breakdown voltage. In the 1960s, in connection with the development of semiconductor technology, which used the operating voltage of Ch. arr. up to 30 V., ceramic k. e. based on thin (≈ 0.2 mm) ceramic films. The use of ferroelectric ceramics as a dielectric made it possible to obtain a specific capacitance of the order of 0.1 μF/cm3. These k.e. it is recommended to install in low-voltage low-frequency circuits. Mica k.e. have low losses, high breakdown voltage and high insulation resistance. Electrodes in mica k.e. made of foil or applied to mica by evaporation of the metal in a vacuum, or by burning. They can be used in radio engineering (electronic filters, blocking circuits, etc.). In metal-paper k. e. the use of metallized plates achieves a higher specific capacitance (compared to paper ones), but the insulation resistance decreases. They have the property of "self-healing" after a single beating. They are not recommended for use in very low pressure circuits. In film c.e. Synthetic is used as a dielectric. film (polystyrene, orgoroplast, etc.). They have a high insulation resistance, large TKE, low losses, relative, low unit cost. In combined c.e. (paper-film) the combined use of paper and film increases the insulation resistance and breakdown voltage, which increases the reliability of the c.e. In electrolytic (oxide) k. e. the dielectric is an oxide film deposited by an electrolytic method on the surface of aluminum plates, which serve as one of the claddings of the CE; the second cladding is a liquid, semi-liquid, or pasty electrolyte or conductor. Such k.e. used in low-frequency direct and pulsating current circuits as blocking capacitors in decoupling circuits, in electric filters, etc. d.

K. e. variable capacity or semi-variable are made with mechanical and electrically controlled capacity. Variable capacitor with TV. dielectric is mainly used as semi-variable (tuner) with a relatively small change in capacitance. K. e. with variable capacity consist of 2 groups of plates, fixed and movable rotary, connected by an axis. When the axis rotates, the rotor plates gradually enter the gaps between them, as a result, the capacitance changes smoothly. That is why capacitors are installed at the crossroads of electrical paths, where it is necessary to separate alternating current from direct current. K. e. they are also used to tune the oscillatory circuits of all radio receivers, in auto devices in electric filters, etc.

In any body there are both positively and negatively charged particles. The process of charging (electrification) consists in the separation of oppositely charged particles in the body.

The simplest capacitor consists of two metal plates (plates) separated by a dielectric layer, which can be air, porcelain, mica, paper or other material with a sufficiently high resistance.

The value characterizing the ability of a capacitor to accumulate an electric charge is called electric capacity and is determined by the formula:

q is the charge of the capacitor, C;

U is the voltage between the capacitor plates,

The letter C represents the capacitance of the capacitor. Per unit capacity

farad (F) is adopted - a tribute to the memory of the famous English scientist Michael Faraday, who at the dawn of the development of electricity conducted numerous experiments with electricity and magnetism. To appreciate what a huge capacitance a farad is, let's say that even the capacitance of the globe is only 0.00071 F.

In practice, for convenience, smaller units are introduced: microfarad (µF), nanofarad (nF) and picofarad (pF). There is such a relationship between them: 1 F \u003d 106 μF \u003d 109 nF \u003d 1012pF; 1 uF - 103nF - 106pF; 1nF = 103pF.

Capacitors are fixed and variable capacity, as well as tuned. UGO and the appearance of some capacitors.

Deciphering the symbols of some capacitors, depending on the material of the dielectric: BM - paper small; BMT - paper small-sized heat-resistant; KJL - ceramic disk; KLS - ceramic cast sectional; KM - ceramic monolithic, KPK-M - trimming ceramic small-sized: KSO - pressed mica; CT - ceramic tubular; MBG - metal-paper sealed; MBGO - metal-paper sealed single-layer; MBM - metal-paper small-sized; ON - film open; PSO - film styroflex open; G1M - small-sized polystyrene.

Contemporary symbol capacitors consists of letters and numbers. The first element - a letter or a combination of letters - denotes a subclass of the capacitor: K - constant capacity; CT - tuning; KP - variable capacity. The second element (number) stands for. a group of capacitors depending on the type of dielectric: 31 - low power mica; 42 - paper metallized; 50 - oxide-electrolytic aluminum; 51 - oxide-electrolytic tantalum, etc.; 52 - volume-porous; 53 - oxide-semiconductor; - polyethylene terephthalate; 2 - tuning and variable capacitors with an air dielectric and 4 with a solid dielectric. The third element is written with a hyphen and corresponds to the serial number of the development.

Try to decipher the types of capacitors yourself: K50-12, K53-16, K73-9, KZl-ll, KT4-21.

For oxide (in the old electrolytic) capacitors of constant capacity, one of the plates in the diagram is marked with a plus (b).

The same sign is also on the capacitor case near the corresponding terminal. It must be remembered that for an oxide capacitor, strict observance of the polarity of the connection of the leads is required. If there is a negative voltage on the positive terminal, the capacitor will not work well or may even fail.

Capacitors of variable capacity and trimmer (c, d) consist of two main elements: a stator and a rotor. When the handle-axis is turned, the rotor moves relative to the fixed stator, as a result of which the capacitance of the capacitor changes.

For fixed capacitors, the diagram next to the UGO indicates the capacitance value in picofarads (pF) or microfarads (μF).

With a capacitance of less than 0.01 μF = 10, the number of picofarads is set without a dimension designation, for example, 15, 220, 9100. For a capacitance of 0.01 μF or more, the number of microfarads is set with the addition of the letters "μ", for example, 0.01 μ, 0 .15 microns, 1 microns, 10 microns. For oxide capacitors, the nominal voltage is additionally indicated (it is written on the capacitor case) - 5 microns x 10 V, 100 microns x 25 V, 100 microns x 50 V. For variable capacitance and tuned capacitors, indicate the limits of capacitance change at the extreme positions of the change in the handle-axis (rotor), for example: 6...30, 10..180, 6...470 (c).

On capacitor cases, nominal capacitances are coded with two or three digits and letters of Russian or Latin alphabet: P (p) - picofarads, N (p) - nanofarads, M (u) - microfarads. Rated capacitances up to 91 pF are expressed in picofarads, using the letter P (p) for designation, from 100 to 9100 pF - in fractions of a nanofarad, and from 0.01 to 0.091 microfarads - in nanofarads, which is denoted by the letter H (n). Capacitances of 0.1 uF or more are expressed in microfarads, using the letter M (μ) for this.

The designation of the capacity unit is placed in front of the number if the capacity is expressed as a decimal fraction: HI5 or n(0.15 nF - 150 pF), M47 or μ 47 (0.47 μF);

instead of a comma if the capacitance is an integer with a decimal fraction: 1P6 or 1r6 (1.6pF), 5H1 or 5n1 (5.1 nF = 5100pF), ZMZ or ZμZ (3.3uF).

The permissible deviation of capacity in percent is marked after the nominal value with numbers or a code: ±1% - F (P), ±2% - G (L), ±5% - J (I), ±10% - K (C), ± 20% - M (V), ± 30% - N (F). (The old notation is in parentheses).

For example, if M47I or u47J is written on the capacitor case, then this is deciphered as follows: 0.47 uF + 5%, and 6H8C (6l8K) means 6.8 nF + 10%.

In addition to the nominal capacitance, capacitance tolerance and rated voltage on the capacitor case there may be information about temperature coefficient capacitance (TKE), which shows the relative change in capacitance with a change in temperature by 1 °C. A positive TKE corresponds to an increase in capacitance when heated, a negative one to a decrease. Depending on the value of TKE, capacitors of constant capacitance are divided into groups. For ceramic capacitors, each group corresponds to a specific body color and a color mark. Due to the fact that TKE is usually not taken into account in amateur practice, we will not consider its coding system.

Capacitors, like resistors, can be connected in parallel or in series. At parallel connection the total capacity can be found by summation.

When connecting oxide capacitors in parallel, it is important to ensure that electrodes of the same polarity are connected together. Remember that the resulting voltage is determined by the minimum operating voltage of the capacitors used.

PICTURE!!!

On fig. shows a circuit consisting of series-connected oxide capacitors having a capacitance of 100 microfarads at an operating voltage of 50V. The operating voltage of a capacitor equivalent to such a connection increases to 200 V (four times), and the capacitance decreases to 25 microfarads. Series connection of capacitors is most often used to increase operating voltages. Next, we will conduct several laboratory studies on the study of capacitors.

Problem solving for new material. When capacitors are connected in parallel, the battery capacity is C \u003d C1 + C2 + C3

The capacitance of the capacitors forming the battery is determined by the formula С1=С2=С3=q/U, then

Homework: abstract

Rear page 160

2., § 8.10; § 8.11.

Rear page 218

Surname, name, group _____________________________________________

	Capacitor capacitance for C, F	Operating voltage U, V	Charged capacitor energy W, J W=CU2/2	Capacitor charge q, C q=CU	Capacitor power P[W]

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Types of capacitors

Capacitors, like resistors, are among the most numerous elements of radio engineering devices.

The basic unit of electrical capacitance is the farad (abbreviated F), named after the English physicist M. Faraday. However, 1 F is a very large capacitance. The globe, for example, has a capacity of less than 1 F. In electrical and radio engineering, they use a unit of capacitance equal to a millionth of a farad, which is called a microfarad (abbreviated microfarad). There are 1,000,000 microfarads in one farad, i.e. 1 uF = = 0.000001 F. But even this unit of capacitance is often too large. Therefore, there is an even smaller unit of capacitance called a picofarad (abbreviated as pF), which is a millionth of a microfarad, i.e. 0.000001uF; 1 uF = = 1,000,000 pF.

All capacitors, whether constant or variable, are characterized, first of all, by their capacitances, expressed respectively in picofarads, microfarads.

On the circuit diagrams the capacitance of capacitors from 1 to 9999 pF is indicated by integers corresponding to their capacitances in these units without pF designation, and the capacitance of capacitors from 0.01 μF (10000 pF) and more in fractions of microfarads or microfarads without μF designation. If the capacitance of the capacitor is equal to an integer number of microfarads, then, in contrast to the designation of capacitance in picofarads, a comma and zero are placed after the last significant digit.

A capacitor in its simplest form consists of two plates separated by a dielectric. If a capacitor is included in the circuit direct current, then the current in this circuit will stop. Yes, this is understandable: through the insulator, which is the dielectric of the capacitor, direct current cannot flow. The inclusion of a capacitor in a DC circuit is tantamount to breaking it. Otherwise, the capacitor behaves in the circuit alternating current. If you include a capacitor in a circuit powered by such a current source, its plates will alternately recharge with the frequency of this current. As a result, alternating current will flow in the circuit.

A capacitor, like a resistor and a coil, offers resistance to alternating current, but it is different for currents of different frequencies. It can pass high frequency currents well and at the same time be almost an insulator for low frequency currents. In this case, the capacitor becomes a kind of filter that passes high-frequency current and delays low-frequency current.

The capacitance of a capacitor to alternating current depends on its capacitance and current frequency: the greater the capacitance of the capacitor and the frequency of the current, the less it capacitance. This capacitor resistance can be determined with sufficient accuracy by the following simplified formula:

where Rc is the capacitance of the capacitor, Ohm; f-current frequency, Hz; C-capacity of this capacitor, F; digit 6 is the value of 2n rounded to integer units (more precisely 6.28, since n = 3,14).

The property of a capacitor not to pass direct current and to conduct alternating currents of different frequencies in different ways is used to separate pulsating currents into their components, delay currents of some frequencies and pass currents of other frequencies.

All fixed capacitance capacitors have conductive plates, and between them - ceramics, mica, paper or some other solid dielectric. According to the type of dielectric used, capacitors are called ceramic, mica, paper, respectively. For ceramic dielectrics, special ceramics serve, the plates are thin layers of silver-plated metal deposited on the ceramic surface, and the leads are brass silver-plated wires or strips soldered to the plates. From above, the capacitor cases are covered with enamel.

Most common ceramic capacitors types KDK (Disk Ceramic Capacitor) and KTK (Tubular Ceramic Capacitor). For a capacitor of the KTK type, one lining is applied to the inner, and the second - to the outer surface of a thin-walled ceramic tube. Sometimes tubular capacitors are placed in sealed porcelain "cases" with metal caps at the ends. These are capacitors of the KGK type.

Ceramic capacitors have relatively small capacitances - up to several thousand picofarads. They are placed in those circuits in which high-frequency current flows (antenna circuit, oscillatory circuit), for communication between them.

To obtain a capacitor of small dimensions, but with a relatively large capacitance, it is made not from two, but from several plates stacked and separated from each other by a dielectric. In this case, each pair of adjacent plates forms a capacitor. By connecting these pairs of plates in parallel, a capacitor of considerable capacity is obtained. This is how all capacitors with a mica dielectric are arranged. Their plates-plates are sheets of aluminum foil or layers of silver applied directly to mica, and the leads are pieces of silver-plated wire. Such capacitors are molded with plastic. These are KSO capacitors. In their name there is a number characterizing the shape and size of capacitors, for example: KSO-1, KSO-5. The larger the number, the larger the capacitor. Some mica capacitors are available in waterproof ceramic cases. They are called SGM type capacitors. The capacitance of mica capacitors is from 47 to 50,000 pF (0.05 microfarads). Like ceramic, they are designed for high-frequency circuits, as well as for use as interlocks and for communication between high-frequency circuits.

In paper capacitors, thin paper impregnated with paraffin serves as a dielectric, and foil is used as the plates. The strips of paper, together with the covers, are rolled up and placed in a cardboard or metal case. The wider and longer the plates, the greater the capacitance of the capacitor.

Paper capacitors are mainly used in low-frequency circuits, as well as for blocking power supplies. There are many types of paper dielectric capacitors. And all have the letter B (Paper) in their designation. Capacitors of the BM type (Paper Small-sized) are enclosed in metal tubes filled with special resin at the ends. KB capacitors have cardboard cylindrical cases. Capacitors of the KBG-I type are placed in porcelain cases with metal end caps connected to the plates, from which narrow output petals extend.

The dielectric of capacitors of the MBM type (Metal Paper Small) is varnished capacitor paper, and the plates are layers of metal less than a micron thick, deposited on one side of the paper.

Electrolytic capacitors are a special group of constant capacitance capacitors. According to the internal structure, an electrolytic capacitor is somewhat reminiscent of a paper one. It has two aluminum foil strips. The surface of one of them is covered with a thin layer of oxide. Between the aluminum strips there is a strip of porous paper impregnated with a special thick liquid-electrolyte. This four-layer strip is rolled up and placed in an aluminum cylindrical cup or cartridge.

The dielectric of the capacitor is an oxide layer. The positive lining (anode) is the tape that has an oxide layer. It is connected to a petal isolated from the body. The second, negative lining (cathode) - paper impregnated with electrolyte through a tape on which there is no oxide layer, is connected to a metal case. Thus, the body is the negative terminal, and the lobe isolated from it is the terminal of the positive lining of the electrolytic capacitor. So, in particular, capacitors of the KE, K50-3 types are arranged. On the schematic diagrams, electrolytic capacitors are depicted in the same way as other capacitors of constant capacitance - with two dashes, but a “+” sign is placed near the positive lining.

Electrolytic capacitors have large capacities - from fractions to several thousand microfarads. They are designed to operate in circuits with pulsating currents, such as filters in AC rectifiers, for coupling between low-frequency circuits. In this case, the negative electrode of the capacitor is connected to the negative pole of the circuit, and the positive electrode to its positive pole. The nominal capacities of electrolytic capacitors are written on their cases. The actual capacity can be much larger than the nominal one.

The most important characteristic of any capacitor, in addition to capacitance, is also its nominal voltage, i.e. the voltage at which the capacitor can operate for a long time without losing its properties. This voltage depends on the properties and thickness of the dielectric layer of the capacitor. Ceramic, mica, paper and metal-paper capacitors of various types are designed for rated voltages from 150 to 1000 V or more. Electrolytic capacitors are produced for rated voltages from a few volts to 30-50 V and from 150 to 450-500 V. In this regard, they are divided into two groups: low voltage and high voltage . The capacitors of the first group are used in circuits with a relatively low voltage, and the capacitors of the second group in circuits with a relatively high voltage.

Capacitors of variable capacity.

Variable capacitors used in tuned receiver circuits consist of two groups of plates made of sheet aluminum or brass. The rotor plates are connected by an axis. The stator plates are also connected and insulated from the rotor. When the axis rotates, the plates of the stator group gradually enter the air gaps between the plates of the rotor group, which is why the capacitance of the capacitor changes smoothly. When the rotor plates are completely removed from the gaps between the stator plates, the capacitance of the capacitor is the smallest; it is called the initial capacitance of the capacitor. When the rotor plates are fully inserted between the stator plates, the capacitance of the capacitor will be greatest, i.e. maximum for this capacitor. The maximum capacitance of the capacitor will be the greater, the more plates it contains and the smaller the distance between the movable and fixed plates.

In small-sized capacitors of variable capacitance, the dielectric can be paper, plastic films, and ceramics. Such capacitors are called variable capacitors with a solid dielectric. While smaller than air dielectric capacitors, they can have significant maximum capacitances. The most common variable capacitors have an initial capacitance of several picofarads and the largest 240-490 pF. Solid capacitors also include tuned capacitors, which are a type of variable capacitor.

Most often, such capacitors are used to adjust the circuits to resonance, so they are called construction capacitors. The capacitance of tuned capacitors is indicated on their cases as a fractional number, where the numerator is the smallest, and the denominator is the largest capacitance of this capacitor.

Capacitors, like resistors, can be connected in parallel or in series. The connection of capacitors is most often resorted to in cases where there is no capacitor of the required rating at hand, but there are others from which the necessary capacity can be made. If capacitors are connected in parallel, then their total capacitance will be equal to the sum of the capacitances of all connected capacitors, i.e.

C total \u003d C1 + C2 + C3, etc.

capacitor capacitance resistance variable

When capacitors are connected in series, their total capacitance is always less than the smallest capacitance included in the chain. It is calculated according to the formula

Ctot = C1-C2 / (C1 + C2)

Changes in the process of changing the strength of capacitors require changing some of the capacitor batteries.

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Subject: Capacitors. The main types of capacitors

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