Register to reply

Capacitors with unequally charged plates?

by gralla55
Tags: capacitors, charged, plates, unequally
Share this thread:
gralla55
#1
Mar15-13, 07:34 PM
P: 57
I'm currently on the chapter on capacitors in my physics book. I'm starting to get the concept, but everything still isn't crystal clear. I get that you can store charges in two plates, one containing a charge of Q, and the other a charge of -Q. But, would it not also work if the charges where unequal to each other in magnitude? Say, if you have one plate with +Q charge and another with -2Q ? Sorry if this is a really obvious question, haha.
Phys.Org News Partner Physics news on Phys.org
Physicists discuss quantum pigeonhole principle
First in-situ images of void collapse in explosives
The first supercomputer simulations of 'spin?orbit' forces between neutrons and protons in an atomic nucleus
Drakkith
#2
Mar16-13, 12:02 AM
Mentor
Drakkith's Avatar
P: 11,532
Sure, you can store different amounts of charges on each plate, but you probably won't find any real world circuits that do that. Capacitors are placed into circuits uncharged and neutral, and the circuits aren't usually capable of charging each plate separately.
sophiecentaur
#3
Mar16-13, 10:43 AM
Sci Advisor
PF Gold
sophiecentaur's Avatar
P: 11,919
If you connect a capacitor to a battery and then put it all on top of a Van der Graaf ball (say, positively charged), there will be an exess of positive charge on both plates of your capacitor. Hence the two pates will have different net charges on them, the positive plate having more and the negative plate having fewer.
Mostly, because the capacity between capacitor plates is much higher than the capacity of the individual plates to Earth and the voltages are all 'low', there will be a very small value of unbalanced charge. But you could say that your suggestion nearly always applies - just not to any significant degree.
In RF circuitry, which could involve C values of only a few pF, the imbalance could be much more significant (although the values of actual charge would be tiny).

technician
#4
Mar16-13, 02:54 PM
P: 1,506
Capacitors with unequally charged plates?

one thing to get clear in your thinking is that if you connect a capacitor to a battery the charge on each plate MUST be equal. The charge removed from one plate is placed on the other plate... so equal.
If you have 2 plate with different charges it cannot be a capacitor connected to a battery.
sophiecentaur
#5
Mar16-13, 06:18 PM
Sci Advisor
PF Gold
sophiecentaur's Avatar
P: 11,919
The capacitor in the OP was not connected to a battery, though. But I think I am still right under those circumstances. Charge the capacitor with +1C on one terminal and -1C on the other, then charge each plate (independently) with another +0.001C (involving a lot of volts, of course). The net result will be +1.001C on one and -0.999C on the other.
I don't think the addition of a battery should alter that.


Register to reply

Related Discussions
Capacitors are charged, disconnected from battery, and had plates swit Introductory Physics Homework 5
Parallel Plates Capacitors, two capacitors. Introductory Physics Homework 0
Capacitors in a circuit as Plates. Introductory Physics Homework 10
Capacitors with more than two plates? Electrical Engineering 6
Capacitors plates again Introductory Physics Homework 4