The Capacitor

Figure 1: Two capacitors (Non-polarized on left and polarized on right)

You can think of a capacitor as a battery with very low capacity. You can charge and
discharge it, just like a battery.

The capacitor is often used to introduce a time-delay in a circuit. For example to
blink a light (check out the example in the Integrated Circuit section). But it’s also
useful for removing noise in an audio signal, or make the power supply of a circuit
more stable.

Capacitors come as polarized and non-polarized capacitors. The biggest difference
is that with the polarized capacitor, you have a positive and a negative pin and you
need to make sure to connect them correctly. You can connect non-polarized capacitors any way you want.

So which one to choose?

You never need your capacitor to be polarized. But for larger values, the capacitors
are made with a material that makes them polarized. So, sometimes you don't
have any choice but to use a polarized one.

Figure 2: Three different variations of the capacitor symbol. If a plus is
shown, it means it’s a polarized capacitor.

Example
By connecting a capacitor in parallel with a resistor and an LED, the capacitor can
store energy and use the energy after the battery is disconnected. This creates a
“fading out”-effect of the LED.

In Figure 3 you can see such a circuit. To build this circuit, you'll need a capacitor
of at least 1000µF to see the effect.

Figure 3: A circuit where the LED fades out because of the energy stored in the capacitor