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What is the working principle of capacitors?

Views:6     Author:Site Editor     Publish Time: 2020-09-14      Origin:Site

Capacitors are a bit like batteries. Although they work in very different ways, they can store electrical energy. If you have read how the battery works, you should know that the battery has two electrodes. Inside the battery, a chemical reaction causes one electrode to generate electrons, and the other electrode absorbs electrons. Capacitors are much simpler. They only store electrons, but cannot generate electrons.


Basic knowledge of capacitors:

The capacitor has two electrodes like a battery. Inside the capacitor, the two electrodes are connected to two metal plates separated by a dielectric. The dielectric can be air, paper, plastic, or any other material that does not conduct electricity and prevents the two metal poles from coming into contact with each other. Using two pieces of aluminum foil and a piece of paper, you can easily make a capacitor. Although the capacitor made in this way has a problem with the storage capacity, it does work.


The capacitor in the electronic circuit is shown in the figure:



When connecting the capacitor and battery together:


The metal plate on the capacitor connected to the negative electrode of the battery will absorb the electrons generated by the battery.

The metal plate on the capacitor connected to the positive electrode of the battery will release electrons to the battery.


After charging, the capacitor and the battery have the same voltage (if the battery voltage is 1.5 volts, the capacitor voltage is also 1.5 volts). Small capacitors have lower capacity, but large capacitors can hold a lot of charge. For example, a soda can-sized capacitor can hold enough charge to light a flashlight bulb for a few minutes. When you see the lightning in the sky, you see a huge capacitor, one of which is the dark cloud in the sky and the other is the earth, and lightning is the phenomenon of charge release between the two "poles" of the dark cloud and the earth. Obviously, such a huge capacitor can hold a lot of charge.


Next, connect the capacitor to the circuit:


There is a battery, a light bulb and a capacitor. If the capacitor is very large, you will see that after connecting the battery, current flows from the battery to the capacitor to charge it, and the bulb will be lit. The bulb will gradually dim, and finally, once the capacitor reaches its capacity, the bulb will immediately go out. Then, you can remove the battery and replace it with a piece of wire. Current will flow from one pole of the capacitor to the other. At this point, the bulb will replay brightly, but the good times are not long, and soon the bulb gradually dims. Finally, the capacitor was discharged (the number of electrons on the two poles of the capacitor was equal), and the light bulb went out again.


Similar to the water tower. The function of the capacitor can be visually described by a water tower connected to the water pipe. The water tower can be used to "storage" the water pressure-when the water supplied by the water pump of the water supply system exceeds the amount of water required by the town, the excess water will be stored in the water tower. Then, when the water demand is high, excess water will flow out of the water tower to maintain the water pressure. Capacitors store electrons in the same way, and they can be released later.


Electric capacity unit:

The unit of electric capacity is law. A capacitor with a capacity of 1 method can store 1 coulomb of electricity at a voltage of 1 volt. One coulomb is 6.25e18 (6.25 * 10 ^ 18, or 62,500,000 trillion) electrons. 1 ampere represents the flow rate of electrons passing through 1 coulomb of electrons per second. Therefore, a capacitor with a capacity of 1 method can store 1 ampere-second of electrons at a voltage of 1 volt.

The 1 method capacitor is usually quite large. Depending on the voltage withstand capacity of the capacitor, it may be as large as a can of gold * fish or a 1 liter soda bottle. Therefore, capacitors are usually measured in microfarads (parts per million).


To understand how big the 1 method is, calculate this way:

A typical alkaline AA battery stores about 2.8 amp-hours of electricity. It means that an AA battery can produce 2.8 amperes of current for 1 hour at 1.5 volts (about 4.2 watt-hours, that is, an AA battery can make a 4 watt bulb continue to illuminate for a little more than an hour). For convenience of calculation, the voltage of the AA battery is counted as 1 volt. To store the energy of one AA battery in a capacitor, a capacitor with a capacity of 3,600 * 2.8 = 10,080 method is required, because 1 amp-hour is equivalent to 3600 amp-seconds. If the capacity of 1 method needs to be stored with a tuna-sized capacitor, then the size of one AA battery is very different from the size of the capacitor storing 10,080 method, which cannot be compared. Unless the voltage resistance of the capacitor is high, it is impractical to use a capacitor to store a large amount of energy.


Application of capacitors:

The difference between a capacitor and a battery is that the capacitor can instantaneously discharge all of its power, while the battery takes several minutes to fully discharge its power. This is why the electronic flash on the camera uses a capacitor: the battery fully charges the flash capacitor in a few seconds, and then the capacitor discharges all the power stored in the flash tube almost instantaneously. This will make charged and large-capacity capacitors extremely dangerous. Therefore, there are warning messages on the flash and the TV to remind people not to open them at will. They all contain large-capacity capacitors that may cause fatal harm to the human body.


The use of capacitors in electronic circuits:

1) Sometimes, capacitors are used to store electricity for high-speed release. This function is used in the flash. Large lasers also use this technique to obtain very bright instant flash effects.

2) The capacitor can also eliminate pulsation. If the line conducting the DC voltage contains pulsations or spikes, the large-capacity capacitor can stabilize the voltage by absorbing the peaks and filling the valleys.

3) The capacitor can block DC. If a smaller capacitor is connected to the battery, after the capacitor is charged (the capacitor capacity is small, the charging process can be completed in an instant), no more current will flow between the two poles of the battery. However, any alternating current (AC) signal can flow through the capacitor unimpeded. The reason is that as the AC current fluctuates, the capacitor continues to charge and discharge as if the AC current was flowing.


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