There is an insulating substance between the two conductors to maintain the electric field, so the capacitance becomes smaller after adding a metal plate. After adding a glass plate, the capacitance becomes larger.

Because the glass will produce polarized charge on the contact surface between the glass and the polar plate after being put in, the overall equivalent charge is less and the electric field intensity is smaller, so more electricity can be stored at the same voltage. Different dielectrics have different relative dielectric constants, and the relative dielectric constant of glass is about 6.

When a voltage is applied between the two plates of the capacitor, the capacitor will store charge. The capacitance of a capacitor is numerically equal to the ratio of the charge on the conductive plate to the voltage between the two plates.

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With the increase of frequency, the capacitance of general capacitors presents a decreasing law. When the capacitor works below the resonant frequency, it is capacitive; When it exceeds its resonant frequency, it is inductive, and at this time it is not capacitance but inductance. Therefore, it is necessary to avoid the capacitor working above the resonant frequency.

In AC circuit, because 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, current flows between capacitors in the form of electric field.

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