Capacitors, often referred to as their ability to contain charge, are capacitors. It is made of two pieces of metal sheet, the middle and then separated by insulating material and constitute. According to the insulation material is not the same, can be made into a wide range of capacitors. Such as: mica, porcelain, paper, electrolytic capacitors, and so on.
In the structure, and is divided into fixed capacitors and variable capacitors. Capacitor actual capacitance and the nominal capacitance of the deviation, said error, in the allowable deviation range called accuracy. A variable capacitor is a capacitor whose capacitance can be adjusted within a certain range, and its capacitance changes correspondingly by changing the relative effective area or inter-chip distance between the pole pieces. Usually used in the radio receiver circuit for tuning capacitors. Capacitors to DC resistance is infinite, that is, the capacitor has a DC effect. The resistance of the capacitor to the alternating current is affected by the alternating current frequency, that is, the capacity of the capacitor is not the same as the frequency of alternating current presents a different capacitive reactance.
Why is the phenomenon of capacitive resistance? The original capacitor is relying on its charge and discharge function to work, the power switch s is not closed. The two metal plates of the capacitor are not charged as well as other general metal plates. When the switch S is closed, the free electrons on the positive plate of the capacitor are attracted by the power supply and pushed to the negative plate. Because the distance between the two plates of the capacitor is insulating, the free electrons running from the positive plate are stacked on the negative plate. Positive plates are positively charged by electron reduction, and negative plates are negatively charged by the gradual addition of electrons.
There is a potential difference between the two plates of the capacitor, and when the potential difference is equal to the supply voltage, the charging of the capacitor is stopped. At this moment if the power cut off, the capacitor can still adhere to the charging voltage. For a charged capacitor, if we connect the two plates together with wires, the electrons pass through the wires and return to the positive plate because the potential difference between the plates is zero. The capacitor is reverberated to the non-charged neutral condition, there is no current in the wire. The frequency of AC current applied to the two plates of the capacitor is high, the number of charge and discharge of the capacitor increases, and the charge and discharge current is enhanced. That is, the blocking effect of the capacitor with respect to the high frequency of the alternating current is reduced, that is, the capacitive resistance is small, whereas the capacitor has a large capacitance due to the low frequency of the alternating current.