The title explains a bit i think.

Im wondering if Direct Current can pass thru capacitors and/or transformers.
I know AC can pass.
Could anyone explain to my why its that way? Plz
"I never liked those Deep Purples or those sort of things. I always hated it. I always thought it was a poor man’s Led Zeppelin"
// Angus Young

+1
dc can pass though them...

AC is from the mains, DC is like battery/after transformer power.
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Dude... i know what ac and dc is! im just wondering if it can pass a transformer/cap or not.
"I never liked those Deep Purples or those sort of things. I always hated it. I always thought it was a poor man’s Led Zeppelin"
// Angus Young

+1
It's been a while since I did pure physics, so I'll say what I remember.
Basically, a capacitor will usually only let a changing signal pass, since it has impedance to a constantly varying current. If you connect DC across it, current will flow but it's not actually passing through it, it's just that electrons on the more positive side are being repelled. This will only happen for a short time (something like e^-t[rc] ) until the capacitor is charged. Eventually, no more electrons will be repelled/attracted at a given voltage, since there won't be enough electromagnetic force. That way, the cap has changing resistance to a DC current.
Transformers are a bit more complex. DC current can pass through a single coil, since it acts just like a resistor. When you first switch on a DC current, you have a changing voltage, which causes a coil to act like an inductor, which may try to oppose a changing voltage by applying back emf, depending on the application. Once the voltage is stable, the current will flow according to V=IR. If you pass AC through a coil, you generally get a higher resistance (impedance) than for DC, since there is magnetic flux interaction. Sending AC through both coils leads to interaction between the two, leading to power transfer from one to the other.
What do you need to know for/what are you making?
In short, no.

Wyld Stallyn is correct, however when you use a transformer the primary and secondary windings aren't connected. What he says is true for an inductor or if you were sending current through one winding on a transformer, but it's not if you're using the transformer in a standard setup.
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I'm a retired Supermod off to the greener pastures of the real world.
Yeah... im too stupid to understand the transformer part :P but the cap part i understand.
Wyld stallin says that DC will flow thru it until its charged , That explains why the led only lit up for a short period of time when i connected it to voltage supply and a cap who was connected in series.
"I never liked those Deep Purples or those sort of things. I always hated it. I always thought it was a poor man’s Led Zeppelin"
// Angus Young

+1
Yeh sorry, I forgot that nothing will flow between the two coils of a transformer unless its alternating current, I was thinking just of inductors really.
this is the breifest i can make it: nothing flows between the coils, the changing current in the first coil generates a changing magnetic flux. the changing magnetic flux then generates a changing current in the second coil. so as a changing flux is needed, a changing current is also needed, and therefore DC does not work with transformers. even ac doesn't pass through them..

"You're a MESS!"
Yeah... Thanks for your help guys!
"I never liked those Deep Purples or those sort of things. I always hated it. I always thought it was a poor man’s Led Zeppelin"
// Angus Young

+1