Capacitors are usually referred to as capacitors for short, and are represented by the letter C. Definition 1: Capacitors, as the name implies, are' charged containers' and devices that contain charges. English name: capacitor. Capacitor is one of the electronic components widely used in electronic equipment, which is widely used in DC isolation, coupling, bypass, filtering, tuning circuit, energy conversion, control circuit and so on. Definition 2. Any two conductors (including wires) are insulated from each other and closely spaced together to form a capacitor. The basic functions of the container-charging and discharging are the basic functions of the capacitor. The process of capacitor charging (storing charge and electric energy) is called charging. At this time, one of the two plates of the capacitor is always positively charged, and the other plate is also negatively charged. Connect one plate of the capacitor to the positive pole of a power supply (such as a battery pack). The other plate is connected to the negative pole of the power supply, and the two plates are charged with different charges of the same amount. After charging, there is an electric field between the two plates of the capacitor, and the electric energy obtained from the power supply during charging is stored in the capacitor. The process of discharging a charged capacitor to lose charge (release charge and electric energy) is called discharge. For example, a wire is used to connect the two poles of a capacitor, and the charges on the two poles neutralize each other. The capacitor will release charge and electric energy. After discharge, the electric field between the two plates of the capacitor disappears and the electric energy is converted into other forms of energy. Capacitance in general electronic circuits, capacitors are often used to realize bypass, coupling, filtering, oscillation, phase shift and waveform conversion. These functions are the evolution of their charging and discharging functions. Power capacitors can be divided into eight types according to their uses: ① shunt capacitors, formerly known as phase-shifting capacitors, are mainly used to compensate reactive power of inductive loads in power systems, so as to improve power factor, improve voltage quality and reduce line losses. ② Capacitors are connected in series in power frequency high voltage transmission and distribution lines to compensate the distributed inductance of the lines, improve the static and dynamic stability of the system and improve the voltage quality of the lines. Extend transmission distance and increase transmission capacity. ③ Coupling capacitors are mainly used for high-frequency communication, measurement, control and protection of high-voltage power lines, and as components in devices for extracting electric energy. (4) Circuit breaker capacitor, formerly known as voltage-sharing capacitor, is connected in parallel with the fracture of EHV circuit breaker to balance the voltage between the interruption ports during the breaking process and improve the arc extinguishing characteristics of the circuit breaker. Improve the breaking ability. ⑤ Electric heating capacitor. Used in electric heating equipment system with frequency of 40 ~ 24000Hz to improve the power factor and voltage or frequency characteristics of the loop. ⑤ Pulse capacitor. Mainly used for energy storage, used as basic energy storage components such as impulse voltage generator, impulse current generator and oscillation circuit for circuit breaker test. ⑤ DC and filter capacitor. Used in high-voltage DC devices and high-voltage rectifier and filter devices. 8 standard capacitor.
2. Basic knowledge of capacitors
Capacitors are usually referred to as capacitors for short, and are represented by the letter C.
Definition 1: Capacitor, as its name implies, is a' charged container' and a device for storing charge. English name: capacitor.
Capacitor is one of the electronic components widely used in electronic equipment, which is widely used in DC isolation, coupling, bypass, filtering, tuning circuit, energy conversion, control circuit and so on. Definition 2: capacitor, any two conductors (including wires) that are insulated from each other and closely spaced form a capacitor.
The basic functions of the container-charging and discharging are the basic functions of the capacitor. The process of charging a capacitor (storing charge and electric energy) is called charging.
At this time, one of the two plates of the capacitor is always positively charged, and the other plate is also negatively charged. Connect one plate of the capacitor to the positive pole of a power supply (such as a battery pack) and the other plate to the negative pole of the power supply, and the two plates will be charged with the same amount of different charges respectively.
After charging, there is an electric field between the two plates of the capacitor, and the electric energy obtained from the power supply during charging is stored in the capacitor. Discharge makes the charged capacitor lose charge (release charge and electric energy), which is called discharge.
For example, if a wire is used to connect the two poles of a capacitor, and the charges on the two poles neutralize each other, the capacitor will release charge and electric energy. After discharge, the electric field between the two plates of the capacitor disappears and the electric energy is converted into other forms of energy.
Capacitance in general electronic circuits, capacitance is often used to realize bypass, coupling, filtering, oscillation, phase shift and waveform transformation, which is the evolution of its charging and discharging functions. Power capacitors can be divided into eight types according to their uses: ① shunt capacitors.
Formerly known as phase shift capacitor. It is mainly used to compensate reactive power of inductive load in power system to improve power factor, improve voltage quality and reduce line loss.
② Series capacitor. It is connected in series in power frequency and high voltage transmission and distribution lines to compensate the distributed inductance of the lines, improve the static and dynamic stability of the system, improve the voltage quality of the lines, extend the transmission distance and increase the transmission capacity.
③ Coupling capacitance. It is mainly used for high-frequency communication, measurement, control and protection of high-voltage power lines, and as a component of the device for extracting electric energy.
④ Circuit breaker capacitor. Formerly known as equalizing capacitor.
Parallel connection plays a role in equalizing the voltage at the fracture of EHV circuit breaker, so that the voltage between the fractures is uniform during and during the breaking process, which can improve the arc extinguishing characteristics of the circuit breaker and improve the breaking ability. ⑤ electrothermal capacitor.
Used in electric heating equipment system with frequency of 40~24000 Hz to improve the power factor and voltage or frequency characteristics of the loop. ⑥ Pulse capacitor.
It mainly plays the role of energy storage, and is used as basic energy storage elements such as impulse voltage generator, impulse current generator and oscillating circuit for circuit breaker test. ⑦ DC and filter capacitor.
Used for high voltage DC devices and high voltage rectifier filter devices. 8 standard capacitance.
It can be used as a standard capacitor or capacitor voltage divider to measure the high voltage in the power frequency and high voltage measurement medium loss loop.
3. Common sense of capacitors
If you are still at school, it is basically enough to know this. In DC circuit, the capacitor is equivalent to an open circuit, which starts with the structure of the capacitor. The simplest capacitor consists of plates at both ends and an insulating dielectric (including air) [1] in the middle. After electrifying, the polar plate is charged, forming a voltage (potential difference), but because there is an insulating substance in the middle, the whole capacitor is not conductive. However, such a situation is under the premise of not exceeding the critical voltage (breakdown voltage) of the capacitor. We know that any substance is relatively insulated. When the voltage across this substance increases to a certain extent, it can conduct electricity. We call this voltage breakdown voltage. Capacitance is no exception. They are not insulators when they are decomposed. But in the middle school stage, such a voltage can't be seen in the circuit, so working below the breakdown voltage can be regarded as an insulator. ceramic capacitor
However, in AC circuit, the direction of current changes with time in a certain functional relationship. The process of capacitor charging and discharging has time. At this time, a changing electric field is formed between the plates, and this electric field is also a function of time. In fact, the current passes between capacitors in the form of a field. Connect AC, block DC,
4. Chapter 8 Physics: Who will talk about current and circuit in detail? PPT should be specific.
1. Charge 1, charged (charged): The rubbed object has the property that light and small objects attract objects, so we say that the object is charged.
Light and small objects refer to pieces of paper, hair, grass balls, dust, light balls and so on. 2. Method of charging objects: 2. Contact charging: Contact charging between objects and charged bodies.
If the charged body touches the electroscope metal ball, it will be charged. ③ Inductive charging: Due to the action of the charged body, the objects near the charged body are charged.
3, two kinds of charges: positive charge: regulation: the electricity carried by the glass rod wiping wire. Essence: atoms in matter lose negative charge: regulation: fur rubs the electricity carried by rubber rods.
Essence: atoms in matter gain extra electrons. 4. the law of interaction between charges: the same kind of charges repel each other, and the different kinds of charges attract each other. 5, electroscope: structure: metal ball, metal bar, metal foil function: check whether the object is charged.
Principle: The principle that like charges repel each other. 6. Charge: Definition: The amount of charge is called electricity.
Unit: Coulomb (C) charge e7. Neutralization: the phenomenon that the same amount of heterogeneous charges are put together to completely cancel out: ① If the positive and negative charges of an object are not equal, neutralization will also occur. At this time, the object with more charge neutralizes the object with less charge, and the remaining charge can make the two objects have the same charge.
Neutralization does not mean eliminating equal amounts of positive and negative charges. In fact, the total charge remains the same, but the positive and negative charges are the same, which makes the whole object appear uncharged. Second, it is currently 1. Formation: the directional movement of charge forms current note: the charge here is free charge.
For metals, free electrons move directionally to form current; For the aqueous solution of acid, alkali and salt, positive and negative ions move directionally to form current. 2. Direction: Specify the direction of positive charge movement as the direction of current.
Note: Outside the power supply, the direction of current is from the positive pole of the power supply to the negative pole. The direction of current is opposite to the direction of directional motion of free electrons. 3. Conditions for obtaining continuous current: The power supply circuit and the current in the circuit have three functions.
(1), thermal effect of current. Such as incandescent lamps and rice cookers.
(2), the magnetic effect of current, such as electric bell. (3) Chemical effects of current, such as electrolysis and electroplating.
Note: the current is invisible and intangible, and we can judge its existence through the action of various currents, which embodies the scientific thought of transformation method. In physics, for some invisible or intangible material or physical problems, we often have to put aside the things themselves and understand the methods of things by observing and studying their explicit characteristics, phenomena or effects in nature. In physics, this method is called transformation. Unit: (1), international unit: A (2), common unit: mA, μA(3), conversion relationship:1a =1000 ma10ma =1000. Symbol: (2) Method: Read clearly the range marked on the terminal and the current value of each battery. Usage rules: two requirements, two requirements, an ammeter should be connected in series in the circuit; (2) The current should flow in from the positive pole of the ammeter and out from the negative pole, otherwise the pointer will reverse.
(3) The measured current shall not exceed the maximum measured value of ammeter. Hazard 1: When the measured current exceeds the maximum measured value of ammeter, it will not only fail to measure the current value, but also bend the pointer of ammeter and even burn the meter.
Second, the scope of choice: the ammeter used in the laboratory has two ranges, 0-0. 6A and 0-3a.
When measuring, first choose a larger range and try to touch it with a switch. If the measured current is 0. If the measured current is less than 0, the current in figs. 6a-3a can be measured.
6A, switch to small range, if the measured current is greater than 3A, switch to large range ammeter. (4) Never connect the ammeter directly to the poles of the power supply without using electrical appliances, because the ammeter is equivalent to a wire.
3. Conductor and insulator: 1. Conductor: Definition: An object that conducts electricity easily. Common materials: metal, graphite, human body, soil, acid-base salt solution. Conductive reason: there are a lot of freely movable charges in the conductor. Description: The current in metal conductor is formed by the directional motion of free electrons, and the current in acid, alkali and salt solution is all positive and negative ions participating in the directional motion. 2. Insulator: Definition: an object that is not easy to conduct electricity.
Common materials: rubber, glass, ceramics, plastics, oil, etc. The reason why it is not easy to conduct electricity: there is almost no charge that moves freely.
3. The difference between "conduction" and "electrification" The conduction process is the process of directional movement of free charge, and the electric conductor is a conductor; The process of charging is the process of gaining and losing electrons. Objects that can be charged can be conductors or insulators. There is no absolute boundary between conductor and insulator, and they can be transformed into each other under certain conditions.
Under certain conditions, insulators can also become conductors. The reason is that heating causes some electrons in the insulator to break free from the bondage of atoms and become free charges.
Fourth, the circuit composition: ② Electrical appliances: Definition: equipment that works with electricity. At work: converting electric energy into other forms of energy.
③ Switch: It controls the on-off of the circuit. Conductor: transmission of electric energy. Three kinds of circuits: ① path: connected circuit.
② Open circuit: open circuit. ③ Short circuit: Definition: The two ends of power supply or electrical appliance are directly connected by wires.
Features: The power supply is short-circuited, and there is a large current in the circuit, which may burn out the insulation of the power supply or conductor and easily cause a fire. 3. Circuit diagram: A diagram showing circuit connections with specific symbols is called a circuit diagram.
4. Connection mode: Series-parallel connection defines a circuit that connects components one by one in sequence. There is only one current path in the circuit to connect the components in parallel, and all the electrical appliances stop working at one point. There are at least two current paths in the circuit, and the elements in each branch work independently and do not affect each other.
The switch function controls the whole circuit. The switch in the main circuit controls the whole circuit. The switch in the branch controls the branch.
Example of circuit diagram Decorate small colored lights, switches and electrical appliances. The common methods to identify the series and parallel connection of various household appliances and street lamps are: (choose the appropriate method to master it skillfully) ① Current analysis method: when identifying the circuit, the current is: power supply positive pole → various appliances → power supply negative pole, if the appliances are not shunted in series on the way; If the current is shunted somewhere, each branch has only one electrical appliance, which is connected in parallel; If each branch has more than one appliance, then the circuit has none.