Views:1 Author:Site Editor Publish Time: 2018-03-27 Origin:Site
Characteristics of capacitors (Alternating current)
A capacitor is a container in which charges are stored. It consists of two pieces of metal near to each other, separated by insulating material. According to the insulating material, a variety of capacitors can be made, such as mica, porcelain, paper, etc. Electrolytic capacitors and so on. In construction, they are divided into fixed capacitors and variable capacitors. Capacitors have infinite force on DC resistance, that is, capacitors have the function of isolating DC. The resistance of capacitors to AC current is affected by AC frequency. That is, capacitors of the same capacity present different capacitive reactance to alternating current at different frequencies. Why do these phenomena occur when the capacitor is switched on? this is because the capacitor depends on its charge-discharge function to work. As shown in Fig. 1, when the power switch s is not closed, the two metal plates of the capacitor and other ordinary metal plates-samples are not charged. When the switch S is closed, as shown in fig. 2, the free electrons on the positive plate of the capacitor are attracted by the power supply and pushed onto the negative plate. Because of the insulation material between the two plates of capacitors, free electrons coming from the positive plate accumulate on the negative plate. The positive plate is charged with the decrease of electrons, and the negative plate takes the negative charge as the electrons increase gradually. There is a potential difference between the two plates of the capacitor. When the potential difference is equal to the voltage of the power supply, the charge of the capacitor stops. If the power supply is cut off, the capacitor can still maintain the charging voltage. For a rechargeable capacitor, if we connect the two plates with a wire, because of the potential difference between the two plates, the electron will pass through the wire and go back to the positive plate. Until the potential difference between the two poles is zero. The capacitor returns to an uncharged neutral state, and there is no current in the conductor. The discharge process of the capacitor is shown in figure 3. The alternating current frequency added to the two plates of the capacitor is high. The number of charges and discharges of capacitors increases, and the current increases; that is to say, capacitors have less resistance to high-frequency alternating current, that is, small capacitive reactance, On the other hand, capacitive reactance of capacitors to low frequency AC is larger. For AC at the same frequency, the larger the capacitance is, the smaller the capacitive reactance will be,and vice versa.