How does a capacitor work?

Question

If I were not mistaken, a capacitor charge itself and only then let electricity flow right?

If that's true, imagine a circuit with a power source, bulb and a capacitor. When I turned up the power source, there should be some lag until the light bulb is turned on right?

Answer 1

A capacitor has the virtue of being able to pass ac but block dc current.

  When a dc voltage is applied to a capacitor the capacitor charges to the voltage of the source.and stays there.

You can discharge the cap but then must charge it again.

  A dc voltage applied to the cap will charge and discharge it in the form of a current.

  The dc goes positive charges the cap then goes negative reversing the process.

  The higher the ac frequency the greater the current passed by the cap.

  An inductor or coil has the opposite effect.

Answer 2

Think of water flowing through a pipe. If we imagine a capacitor as being a storage tank with an inlet and an outlet pipe, it is possible to show approximately how an electronic capacitor works.

First, let's consider the case of a "coupling capacitor" where the capacitor is used to connect a signal from one part of a circuit to another but without allowing any direct current to flow.

water tank analogy for capacitor



If the current flow is alternating between zero and a maximum, our "storage tank" capacitor will allow the current waves to pass through.

water tank analogy for capacitor



However, if there is a steady current, only the initial short burst will flow until the "floating ball valve" closes and stops further flow.

capacitor symbol



A coupling capacitor is represented like this

So a coupling capacitor allows "alternating current" to pass through because the ball valve doesn't get a chance to close as the waves go up and down. However, a steady current quickly fills the tank so that all flow stops.

Answer 3

to answer your other question: "circuit with a power source, bulb and a capacitor. When I turned up the power source, there should be some lag until the light bulb is turned"

Depends on how you wired up the circuit and on whether the power is AC or DC.

1) DC, cap in series. The bulb may flash briefly as the cap charges, but once it is charged, there is no current.

2) DC, cap parallel with bulb. There may be a slight delay, probably very small, before the light goes on until the cap gets charged. Probably won't be noticable.

3) AC, cap in series. Depends on the value of the cap. Large cap, AC current goes through with no problem. As you reduce the cap, it drops more and more voltage, and the lamp gets dimmer.

4) AC, cap in parallel. Light will go on, but there will be more current drawn from the supply, some for the light, some for the cap.