Electronics electrolytic capacitor blocking DC but passing AC demonstration circuit explained

Novice question: But, if you are using a 9V+ battery [and a battery delivers DC, right?] then what/WHERE is the AC that you are letting through, coming from? It’s a DC battery NOT an AC battery, what is producing AC voltage in this circuit? Please let me know, I’m trying to learn more about this stuff. Cheers!

Technically speaking, you have pulsed DC, not AC since it does not alternate (i.e. reverse and go below your 0v reference). So the capacitor is really passing the changes in current. AC just happens to be one way to do that, but I don't believe your circuit is truly AC, it's pulsed DC.

What is the value of capacitor?

Thank you very much.

IS there any reason why one can not place the pos term of a dc electrlitic capacitor to the hot leg of the grid (AC) and the neutral to the neg terminal of the capacitor assuming the capacitor is rated for more than the grid's voltage???