Problems about triode and capacitor.

I tried to answer with metaphor, the purpose is to make you understand, please don't joke.

Triode: The emitter and collector are all in one tube, which is made of the same material and can flow under the action of electric field. The base is like adding a straw cutter in the middle of the pipe, and the material properties of the straw cutter are opposite to those on both sides of the pipe. If this substance can be reversed by electric field, then when there is an electric field on the straw cutter to reverse its properties, all the substances in the tube are the same at this time. Under the action of the electric field at both ends of the tube, the material in the tube flows directionally. When the electric field acts on the straw cutter, the small straw cutter controls the material flow in the big pipe.

Capacitance: Think of it as two metal plates insulated in the middle. When an electric field is applied to both sides, all electrons in the connected plates are "sucked away" by the positive power supply, leaving a positive charge on the plate, while the other plate is just the opposite. Because they are insulated, positive and negative charges keep each other, just as DC current cannot "flow" through a capacitor. When the external electric field changes, the positive and negative charges "flow away" in the opposite direction, and so on.