The discussion revolves around determining the charge on the plates of a parallel plate capacitor given the area and separation between the plates. Participants explore the relationship between capacitance, voltage, and charge in the context of electrostatics.
The discussion is ongoing with various interpretations being explored. Some participants have provided guidance on the relationships between charge, voltage, and capacitance, while others are questioning the assumptions made about charge distribution and grounding.
There are discussions about the implications of grounding on charge distribution, the assumptions regarding voltage references, and the potential for different charge distributions on the plates based on their connections in the circuit.
That's the 'perfect' description of the circuit.gneill said:
You can see it here.gracy said:
If there is a voltage connected to plates then it is impossible that plates would be neutral?gneill said:
In general plates can be neutral, but they don't have to be if there are external connections over which charges can enter or leave them. Isolated plates are always neutral unless some charge has been deposited on them by some agency.gracy said:
here voltage supplier and earth?gneill said:
Right.gracy said:
While that is all true, I'm not sure that introducing that distinction at this juncture is going to help Gracy with the immediate details that she needs to clear up. Perhaps it can be addressed as a new topic later?jbriggs444 said:
That would depend upon whether or not the connects lead to something that will cause charge to flow (impose potential differences). Even so it is possible to arrange things so that the net excess charge will be zero! Here's an example:gracy said:
But plate A and C have plus charges,right?gneill said:
Seeing this diagram,can I say there won't be net charge on any plate because there isn't any 'closed electrical path "through" the dielectric'?gneill said:
No, one will be plus, the other minus. Look at the polarities of the two batteries. One establishes plate a at +V potential with respect to ground, the other establishes plate c at -V potential with respect to ground.gracy said:
Yeah..right..gneill said:
No, the electric fields between the plates established by the potential differences suffices to influence charge movement in the plates and wiring. Remove the central plate from the scenario and you have a typical capacitor with a potential difference of 2V across it.cnh1995 said:
So can I conclude plates A and C form a capacitor with space between them as dielectric and middle metal plate is just "polarized" because of the the electric field of the two plates.gneill said:
Plate b would have negative charges on it because of plate a and would have positive charges on it because of plate c,right?gneill said:
Effectively yes, but note that the gaps between the middle plate and the outer ones are much smaller than the gap between the two outer plates. So the "new" capacitors thus formed will have higher capacitance than the two outer plates alone would have (recall the formula for capacitance of a parallel plate capacitor).cnh1995 said:
Right.gneill said:
Correct.gracy said:
Yes. The middle plate alone will have -ve charge whose magnitude will be twice the +ve charge on each plate.gracy said:
I did not understand.Why can not Earth take or give any charges to plate b?gneill said:
Right. Sometimes it helps to sketch in the electric field lines that are imposed by the potential differences, and recall that electric field lines always begin on a positive charge and end on a negative charge.gracy said:
Because Earth can give as much plate needs.cnh1995 said:
It can. But it doesn't in this case. The situation calls for equal amounts of + and - charges on the middle plate, for a net sum of zero charge.gracy said:
But Earth does not give them.Plate b already possesses that.gneill said:
That's one way to look at it.gracy said:
Correct.gracy said: