Why is there confusion about capacitors and potential difference between plates?

[Alex Hughes]

So I understand that a capacitor consists of 2 plates separated by a distance which creates a potential difference between the plates. But I was confused, when watching this physics video it seemed to be saying that once the capacitor was fully charged, the plate closest to the positive terminal of the battery was at a lower potential than the other plate. Wouldn't it be the other way around though? Once the circuit is connected wouldn't the electrons be forced away from the plate closer to the positive terminal resulting in a higher potential, and the plate closer to the negative terminal would have a build up of electrons having a lower potential.
Here is the video I was referring to: If you start at the 3:12 mark you can see that the plate closer to the negative terminal is at a higher potential. Is this video incorrect or are they thinking in terms of conventional current? Would love some feedback. Thanks.

 

[scottdave]

They say that "voltage is shown upside-down" because they are using electron flow

 

[Alex Hughes]

They say that "voltage is shown upside-down" because they are using electron flow

Yea, but just because you're using electron flow, it doesn't change the potential of the capacitors right? The electrons will just be flowing from a low to a high potential, but the capacitor would still have a lower potential on the plate closer to negative terminal. The only thing that would change is the direction of the current?

 

[scottdave]

There may have been something with the way they created their animation, so perhaps that is why they just added the statement about being upside down rather than redoing the animatio. That is my guess.

 

[Alex Hughes]

There may have been something with the way they created their animation, so perhaps that is why they just added the statement about being upside down rather than redoing the animatio. That is my guess.

Ok, thank you.

 

[Guineafowl]

I think the animation is correct - voltage is defined as the amount of energy required to move a unit of charge between the measurement points, ie joules per coulomb.

The sign of the charge is not specified, but it’s clearly implied that the direction of movement must be against the charge gradient (work must be done, against electrostatic repulsion).

If you start with negative charges, as in the video, the potential differences are reversed but still correct. It would still take work to move an electron from the low plate to the high plate of the capacitor. Similarly, work has been done to push the electrons to the upper plate, so the charges there are at a higher potential than the lower. The notional heights are valid.

If you start with positive charges, as convention dictates, all is reversed. Voltmeters measure with this convention in mind, for historic reasons. We say the positive terminal of a car battery is 12 volts above the negative - it would take 12 joules to move a coulomb of positive charge from neg to pos. But it would take 12 joules to move a coulomb of negative charge the other way.

Electrical potential difference (voltage) is about energy, and can be thought of in terms of height, like with gravity. Which way ‘up’ you are depends of the sign of the charges.

 

[sophiecentaur]

This is yet another example of where using electrons when dealing with basic electrics is very likely to confuse.
Charge, Current and Potential are all you need. Electrons are for later on, when you no longer have a problem just going along with the Maths (and getting it reliably correct, of course). If I had £1 for every student who tried to insist "They got it wrong about Electric Current Flow" I would be a wealthy man.
Also, beware of many animations which can sometimes be no better than Hollywood output.

 

[Windadct]

The whole "debate" drives me nuts.

 

[sophiecentaur]

The whole "debate" drives me nuts.

There was no debate until non-Scientists started trying to teach Science and tried make it easy for everybody. It drives me nuts too.

 

[Guineafowl]

The single most execrable sin in the media is speaking of ‘volts going through you’.