"In analog circuits, a coupling capacitor is used to connect two circuits such that only the AC signal from the first circuit can pass through to the next while DC is blocked. This technique helps to isolate the DC bias settings of the two coupled circuits. Capacitive coupling is also known as AC coupling and the capacitor used for the purpose is also known as a DC-blocking capacitor."
Here is an example of use of it:
Below another example from a question on this website:
And here is an example from an electronics text book:
What determines the orientation of the coupling capacitors here? Is that the Vcc voltage? But if so, the last example does not follow the first two. Which one is correct and why?
Below a polarized cap is used with an AC signal. There is no DC level. As you see the voltage across the cap is alternating from +7V to arounf -7V? Is this acceptable?