Views:6 Author:Site Editor Publish Time: 2018-01-20 Origin:Site
The capacitor is a container in which charges are stored. It is composed of two pieces of metal close to each other, separated by insulating material, depending on the insulating material. Can be made into a variety of capacitors, such as: mica, porcelain dielectric, paper dielectric, electrolytic capacitors, etc. In construction, they can be divided into fixed capacitors and variable capacitors. The resistance of capacitor to AC 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, as showed in figure 1. When the power switch s is not closed, the two metal plates and other ordinary metal plates of the capacitor are not charged. When the switch S is closed, as showed in fig. 2, the free electrons from the positive plate of the capacitor are attracted by the power supply and pushed onto the negative plate. Because there is insulation between the two plates of the capacitor, the free electrons that run from the positive plate accumulate on the negative plate. The positive plate is positively charged by the reduction of electrons. The negative plate is negatively charged by the gradual increase of electrons. There is a potential difference between the two plates of the capacitor. When the potential difference is equivalent to the voltage of the power supply, the charge of the capacitor stops. If the power supply is stopped off, the capacitor can still maintain the charging voltage. For a rechargeable capacitor, if we connect the two plates with a wire, the electron will pass through the wire and return to the positive plate because of the potential difference between the two plates. Until the potential difference between the two poles is zero. The capacitor returns to a neutral state without charge. The discharge process of the capacitor is illustrated in Fig. 3. The frequency of alternating current added to the two plates of the capacitor is high, and the charge and discharge times of the capacitor increase; The charge-discharge current is also enhanced; In other words, capacitors have less resistance to high-frequency alternating current, that is, small capacitive reactance. On the other hand, capacitive reactance of capacitors with low frequency AC is larger. For AC at the same frequency, the larger the capacitor capacity, the smaller the capacitive reactance, the smaller the capacitive reactance.