Presentation for 8th grade on the physics of capacitors. Presentation on the topic "capacitor". their relative position
“Capacitors. Electrical capacity »
Purpose: To form an idea of a capacitor, about the electrical capacity of a capacitor, to introduce a unit of measurement of electrical capacity, to consider the dependence of the capacitance of a capacitor on its geometric design.
1 . Coulomb's law: 2. The force characteristic of the field is... 3. The intensity can be found using the formula: 4. Field intensity of a point charge: 5. Field intensity of a plane: 6. The direction of the intensity is taken... 7. The energy characteristic of the field is... 8. Give the characteristic Let's repeat...
A capacitor consists of two conductors separated by a dielectric layer, the thickness of which is small compared to the size of the conductors. Capacitor
Designation of a capacitor in an electrical diagram. - + + + + + - - - - E - q + q
If two conductors isolated from each other are given charges q 1 and q 2, then a certain potential difference Δφ arises between them, depending on the magnitude of the charges and the geometry of the conductors. The potential difference Δφ between two points in an electric field is often called voltage and is symbolized by the letter U. Of greatest practical interest is the case when the charges of the conductors are identical in magnitude and opposite in sign: q 1 = – q 2 = q. In this case, we can introduce the concept of electrical capacitance.
The electrical capacity of the capacitor is equal to where q is the charge of the positive plate, U is the voltage between the plates. The electrical capacity of a capacitor depends on its geometric design and the electrical permittivity of the dielectric filling it and does not depend on the charge of the plates.
According to the principle of superposition, the field strength created by both plates is equal to the sum of the strengths and fields of each of the plates:
Outside the plates, the vectors and are directed in different directions, and therefore E = 0. The surface charge density σ of the plates is equal to q / S, where q is the charge and S is the area of each plate. The potential difference Δφ between the plates in a uniform electric field is equal to Ed, where d is the distance between the plates. From these relationships we can obtain a formula for the electrical capacity of a flat capacitor, where ε o =8.85·10 -12 F/m is the electrical constant.
Thus, the electrical capacity of a flat capacitor is directly proportional to the area of the plates (plates) and inversely proportional to the distance between them. If the space between the plates is filled with a dielectric, the electrical capacity of the capacitor increases by ε times:
Capacitors can be connected to each other to form capacitor banks. When connecting capacitors in parallel (Figure No. 3), the voltages on the capacitors are the same: U 1 = U 2 = U, and the charges are equal to q 1 = C 1 U and q 2 = C 2 U. Such a system can be considered as a single capacitor of electrical capacity C, charged with a charge q = q 1 + q 2 at a voltage between the plates equal to U. this implies
Thus, when connected in parallel, the electrical capacitances add up. Parallel connection of capacitors. C = C 1 + C 2. Series connection of capacitors. .
When connected in series (Figure 4), the charges of both capacitors are the same: q 1 = q 2 = q, and the voltages across them are equal and Such a system can be considered as a single capacitor charged with charge q at a voltage between the plates U = U 1 + U 2. Hence,
Types of capacitors
Application of capacitors Types of capacitors: - air, - paper, - mica, - electrostatic. Purpose: To accumulate charge or energy for a short time to quickly change the potential. Do not pass direct current. In radio engineering - oscillatory circuit, rectifier. Application in photographic equipment.
Variable capacitors with air or solid dielectric Variable capacitors with air or solid dielectric are often used. They consist of two systems of metal plates insulated from each other. One system of plates is stationary, the second can rotate around an axis. By rotating the moving system, the capacitance of the capacitor is smoothly changed.
Pinned3Zie. What are capacitors used for? How does a capacitor work? Why is the space between the capacitor plates filled with dielectrics? What is the electrical capacity of a charged capacitor? What does electrical capacity depend on? Consolidation.
The distance between the plates of a square flat capacitor with a side of 20 cm is 1 mm. What is the potential difference between the plates if the charge of the capacitor is 2 nC. task
: Solution:
Lesson summary: What new or interesting things did you learn in class today? What did you study?
Homework: § 99, 100 Ex. 18
“Capacitor physics” - Types of capacitors. - Paper capacitor - mica capacitor electrolytic capacitor. Air condenser. Capacitor connections. - Air condenser. Definition of a capacitor. When connecting an electrolytic capacitor, polarity must be observed. Purpose of capacitors.
“Using capacitors” - Experiments with a capacitor. The capacitor is used in ignition circuits. Energy formulas. Application of capacitors. Features of the use of capacitors. The capacitor is used in medicine. Lamps with discharge lamps. Capacitive keyboard. Capacitor. Cell phones. Used in telephony and telegraphy.
“Electrical capacity and capacitors” - In the computer keyboard. Variable capacitor. Connection of capacitors. Electrical capacity. Consistent. Flashlights. Capacitor connection diagrams. Designation on electrical diagrams: Capacitors. Electrical capacity of a flat capacitor. The entire electric field is concentrated inside the capacitor.
“Use of capacitors” - For the latter batteries, regeneration time is fundamentally important. Polymer capacitors with solid electrolyte on the chipset. Diagram of a telephone bug. Current rectifier circuit. Capacitor CTEALTG STC - 1001. Condenser microphone. A successful association is on the Sciencentral website. Studio condenser directional microphone for wide applications.
“Capacitor” - Capacity of the capacitor. Charge ratio. Capacitor energy. Variable capacitor. Paper capacitor. Square. Capacitor. Application of capacitors. Physics lesson in 9th grade
General purpose capacitors are capacitors used in most types of electronic equipment. No special requirements apply to capacitors of this type. Special purpose capacitors are all other capacitors. These include: pulse, high-voltage, starting, noise suppression, as well as other capacitors.
Fixed capacitors are capacitors whose capacitance is fixed and does not change during operation of the equipment. Variable capacitors - used in circuits where capacitance changes during operation are required. In this case, the capacitance can be changed in various ways: mechanically, by changing the control voltage, by changing the ambient temperature.
Unprotected capacitors are a type of capacitors that are not allowed to operate in conditions of high humidity. It is possible to operate these capacitors as part of sealed equipment. Protected capacitors - can operate in conditions of high humidity.
Non-insulated capacitors - when using this type of capacitors, they are not allowed to touch the equipment chassis with their housing. Insulated capacitors - have a well-insulated housing, which makes it possible to touch the equipment chassis or its live surfaces. Sealed capacitors - this type of capacitor uses a housing sealed with organic materials. Sealed Capacitors - These capacitors have a sealed housing, which eliminates the interaction of the internal structure of the capacitor with the environment.
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MINISTRY OF EDUCATION AND SCIENCE OF THE RF GBPOU "Technological College named after. N.D. Kuznetsova" SPECIALTY INFORMATION SYSTEMS Presentation on physics on the topic: "Capacitors" Prepared by: 1st year student Victoria Sergeevna Vidyasova Scientific supervisor: Olga Vasilievna Kurochkina Samara, 2016.
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Introduction: Definition Types of capacitors Marking of capacitors Application of capacitors
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DEFINITION A capacitor is an electrical (electronic) component constructed from two conductors (plates) separated by a dielectric layer. There are many types of capacitors and they are mainly divided according to the material of the plates themselves and the type of dielectric used between them.
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Types of capacitors Paper and metal capacitors In a paper capacitor, the dielectric separating the foil plates is special capacitor paper. In electronics, paper capacitors can be used in both low-frequency and high-frequency circuits. Sealed metal-paper capacitors, which instead of foil (as in paper capacitors) use vacuum deposition of metal onto a paper dielectric, have good quality electrical insulation and increased specific capacitance. A paper capacitor does not have great mechanical strength, so its filling is placed in a metal case, which serves as the mechanical basis of its design.
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Electrolytic capacitors In electrolytic capacitors, unlike paper capacitors, the dielectric is a thin layer of metal oxide formed electrochemically on a positive cover of the same metal. The second cover is a liquid or dry electrolyte. The material that creates the metal electrode in an electrolytic capacitor can be, in particular, aluminum and tantalum. Traditionally, in technical jargon, “electrolyte” refers to aluminum capacitors with a liquid electrolyte. But, in fact, tantalum capacitors with solid electrolyte also belong to electrolytic capacitors (they are less common with liquid electrolyte). Almost all electrolytic capacitors are polarized, and therefore they can only operate in DC voltage circuits while maintaining polarity. In case of polarity reversal, an irreversible chemical reaction may occur inside the capacitor, leading to the destruction of the capacitor, even to its explosion due to the gas released inside it. Electrolytic capacitors also include the so-called supercapacitors (ionistors) with an electrical capacity that sometimes reaches several thousand Farads.
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Aluminum Electrolytic Capacitors Aluminum is used as the positive electrode. The dielectric is a thin layer of aluminum trioxide (Al2O3), Properties: they work correctly only at low frequencies have a large capacitance Characterized by a high capacitance-to-size ratio: electrolytic capacitors are usually large in size, but capacitors of a different type, the same capacitance and breakdown voltage would be much larger in size. They are characterized by high leakage currents and have moderately low resistance and inductance.
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Tantalum electrolytic capacitors This is a type of electrolytic capacitor in which the metal electrode is made of tantalum and the dielectric layer is made of tantalum pentoxide (Ta2O5). Properties: high resistance to external influences, compact size: for small ones (from several hundred microfarads), size comparable to or smaller than aluminum capacitors with the same maximum breakdown voltage, lower leakage current compared to aluminum capacitors.
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Polymer capacitors Unlike conventional electrolytic capacitors, modern solid-state capacitors have a polymer dielectric instead of an oxide film used as a plate separator. This type of capacitor is not subject to swelling and charge leakage. The physical properties of the polymer contribute to the fact that such capacitors are characterized by high pulse current, low equivalent resistance and a stable temperature coefficient even at low temperatures. Polymer capacitors can replace electrolytic or tantalum capacitors in many circuits, such as filters for switching power supplies, or in DC-DC converters.
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Film capacitors In this type of capacitor, the dielectric is a plastic film, for example, polyester (KT, MKT, MFT), polypropylene (KP, MKP, MFP) or polycarbonate (KC, MKC). Electrodes can be deposited on this film (MKT, MKP, MKC) or made in the form of a separate metal foil, wound into a roll or pressed together with a dielectric film (KT, KP, KC). The modern material for capacitor film is polyphenylene sulfide (PPS). General properties of film capacitors (for all types of dielectrics): they work properly at high current have high tensile strength have a relatively small capacitance minimum leakage current used in resonant circuits and RC snubbers Individual types of film differ in: temperature properties (including with the sign temperature coefficient of capacity, which is negative for polypropylene and polystyrene, and positive for polyester and polycarbonate) maximum operating temperature (from 125 °C, for polyester and polycarbonate, up to 100 °C for polypropylene and 70 °C for polystyrene) resistance to electrical breakdown , and therefore the maximum voltage that can be applied to a certain film thickness without breakdown.
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Ceramic capacitors This type of capacitors is made in the form of one plate or a pack of plates from a special ceramic material. Metal electrodes are sprayed onto the plates and connected to the terminals of the capacitor. The ceramic materials used can have very different properties. The diversity includes, first of all, a wide range of relative electrical permeability values (up to tens of thousands, and this value is found only in ceramic materials). Such a high permeability value allows the production of ceramic capacitors (multilayer) of small sizes, the capacitance of which can compete with the capacitance of electrolytic capacitors , and at the same time working with any polarization and characterized by less leakage. Ceramic materials are characterized by a complex and nonlinear dependence of parameters on temperature, frequency, and voltage. Due to the small size of the case, this type of capacitor has a special marking.
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How are large capacitors marked? To correctly read the technical specifications of a device, some preparation is necessary. You need to start studying with units of measurement. To determine capacitance, a special unit is used - farad (F). The value of one farad for a standard circuit seems too large, so household capacitors are marked in smaller units. The most commonly used is mF = 1 µF (microfarad), which is 10-6 farads.
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When calculating, an off-label unit can be used - millifarad (1mF), which has a value of 10-3 farads. In addition, designations can be in nanofarads (nF) equal to 10-9 F and picofarads (pF) equal to 10-12 F. Capacitance markings for large capacitors are applied directly to the housing. In some designs, the markings may differ, but in general, you need to be guided by the units of measurement mentioned above.
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Designations are sometimes written in capital letters, for example, MF, which actually corresponds to mF - microfarads. The marking fd is also found - an abbreviated English word farad. Therefore mmfd will correspond to mmf or picofarad. In addition, there are designations that include a number and one letter. This marking looks like 400m and is used for small capacitors. In some cases, it is possible to apply tolerances, which are an acceptable deviation from the rated capacitance of the capacitor. This information is of great importance when, when assembling certain types of electrical circuits, capacitors with precise capacitance values may be required. If we take the marking 6000uF + 50%/-70% as an example, then the maximum capacitance value will be 6000 + (6000 x 0.5) = 9000 uF, and the minimum 1800 uF = 6000 - (6000 x 0.7).
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If there are no percentages, you need to find the letter. Usually it is located separately or after the numeric designation of the container. Each letter corresponds to a specific tolerance value. After this, you can begin to determine the rated voltage. With large capacitor housing sizes, voltage markings are indicated by numbers followed by letters or letter combinations in the form V, VDC, WV or VDCW. The WV symbols correspond to the English phrase WorkingVoltage, which means operating voltage. Digital readings are considered to be the maximum permissible capacitor voltage, measured in volts.
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If there is no voltage marking on the device body, such a capacitor should only be used in low-voltage circuits. In an AC circuit, use a device designed specifically for this purpose. Capacitors designed for direct current cannot be used without the ability to convert the rated voltage. The next step is to identify the positive and negative symbols that indicate the presence of polarity. Determining the positive and negative is of great importance, since incorrect determination of the poles can lead to a short circuit and even explosion of the capacitor. In the absence of special symbols, the device can be connected to any terminals, regardless of polarity.
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The pole designation is sometimes applied in the form of a colored stripe or a ring-shaped indentation. This marking corresponds to the negative contact in electrolytic aluminum capacitors, which are shaped like a tin can. In very small tantalum capacitors, these same symbols indicate positive contact. If there are plus and minus symbols, the color coding can be ignored. Other markings. The markings on the capacitor body allow you to determine the voltage value. The figure shows special symbols that correspond to the maximum permissible voltage for a particular device. In this case, parameters are given for capacitors that can only be operated at constant current.
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Application of capacitors. The energy of a capacitor is usually not very high - no more than hundreds of joules. In addition, it is not preserved due to the inevitable charge leakage. Therefore, charged capacitors cannot replace, for example, batteries as sources of electrical energy. Capacitors can store energy for a more or less long time, and when charged through a low-resistance circuit, they release energy almost instantly. It is this property that is widely used in practice. A flash lamp used in photography is powered by the electric current of a capacitor discharge, which is pre-charged by a special battery. Excitation of quantum light sources – lasers – is carried out using a gas-discharge tube, the flash of which occurs when a bank of capacitors of large electrical capacity is discharged. However, capacitors are mainly used in radio engineering...
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