Review Content video: Circuits and Ohm's law

lotus0618
Posts: 182
Joined: Sun Dec 29, 2019 5:47 pm

Review Content video: Circuits and Ohm's law

Regarding the question, I'd like to make sure that I completely understand this material. The reason why I didn't chooose the option "the charge held on the capacitor plates (when fully charged) will increase" cause i thought once it's full charged, we cannot add more charges onto the capacitor plates. Is this thought process only correct when there's no change in the capacitor's characteristics? here, the distance of the capacitor plates is halved so the capacitor's capacitance can now hold more charges.
Attachments
circuits got wrong.png
NS_Tutor_Mathias
Posts: 616
Joined: Sat Mar 30, 2019 8:39 pm

Re: Review Content video: Circuits and Ohm's law

If capacitance increases, charge stored in the plates must increase (Q=CdeltaV, meaning at a constant potential, Q is directly proportional to C >as long as I wait until the capacitor is fully charged<).

The reason this says "once fully charged" means that if I simply halve the distance between the two plates, the charge stored in each plate does NOT immediately double - in fact, it stays the same. I still need to do WORK to charge this capacitor, I need to move those charges over a distance (which takes time, in other words I need to do WORK over TIME, meaning I need a source of power [in this case the battery]).
lotus0618
Posts: 182
Joined: Sun Dec 29, 2019 5:47 pm

Re: Review Content video: Circuits and Ohm's law

Sorry for a late question to your explanation. Am I correct for saying that the charge held on the capacitor plates (when fully charged) will not increase or decrease because it's already fully charged, regardless of the change in the distance between its plates?
NS_Tutor_Mathias
Posts: 616
Joined: Sat Mar 30, 2019 8:39 pm

Re: Review Content video: Circuits and Ohm's law

No. Changing the distance between the plates changes what 'maximum charge' of that capacitor is - as in, it changes how much charge it can hold. The "once fully charged" stipulation is that if I increase the charge my parallel plate capacitor can hold, it doesn't magically charge up. I need a power source for that to happen.
lotus0618
Posts: 182
Joined: Sun Dec 29, 2019 5:47 pm

Re: Review Content video: Circuits and Ohm's law

oh gottcha, thanks