Sam Ayre said:

occurs between an energized conductor and a non energized conductor due to the difference in potential difference

Just one thing that I don't think has been picked up in the excellent replies - better to think of "at least one energized conductor". You've picked up the important point that you'll notice the effect if there's a potential difference. This may be between, say, one conductor at 230V and another at 0V (one energized, one non-energized using your wording), or one at 230V and one at 110V in phase so 120V potential difference, or both at 110V but in opposite phases so 220V potential difference between them.

It's all about the potential difference.

Sam Ayre said:

Would the same thing occur on a DC circuit or does the capacitor just build up until it's full and then discharge once the DC voltage is removed? 

Basically yes, the rate of charge falls exponentially over time. So initially (when the voltage is first applied) there's a high charge and it drops away until it becomes immeasurably small. And the same with the discharge.

This is important as it explains the behaviour of capacitive coupling for ac signals. For faster ac signal changes (higher frequency) the charging / discharging spends a higher proportion of its time at that initial high charge point, it can't do much charging before it has to start discharging. This is why as the frequency goes up you see more average current being drawn to carry out this charging / discharging. We tend to think of this as ac current "flowing through" the capacitor (and I find that a perfectly workable way of thinking of it), but it isn't really.

Cheers, Andy

Sam Ayre said:

occurs between an energized conductor and a non energized conductor due to the difference in potential difference

Just one thing that I don't think has been picked up in the excellent replies - better to think of "at least one energized conductor". You've picked up the important point that you'll notice the effect if there's a potential difference. This may be between, say, one conductor at 230V and another at 0V (one energized, one non-energized using your wording), or one at 230V and one at 110V in phase so 120V potential difference, or both at 110V but in opposite phases so 220V potential difference between them.

It's all about the potential difference.

Sam Ayre said:

Would the same thing occur on a DC circuit or does the capacitor just build up until it's full and then discharge once the DC voltage is removed? 

Basically yes, the rate of charge falls exponentially over time. So initially (when the voltage is first applied) there's a high charge and it drops away until it becomes immeasurably small. And the same with the discharge.

This is important as it explains the behaviour of capacitive coupling for ac signals. For faster ac signal changes (higher frequency) the charging / discharging spends a higher proportion of its time at that initial high charge point, it can't do much charging before it has to start discharging. This is why as the frequency goes up you see more average current being drawn to carry out this charging / discharging. We tend to think of this as ac current "flowing through" the capacitor (and I find that a perfectly workable way of thinking of it), but it isn't really.

Cheers, Andy