Parallel plate capacitor electric field problem

AI Thread Summary
A parallel-plate capacitor is formed by two circular disks spaced 0.50 mm apart, with 1.8*10^9 electrons transferred, resulting in an electric field strength of 1.3*10^5 N/C. The relevant equations for solving the problem include the electric field equation and the relationship between charge, area, and permittivity. Participants express frustration with the precision required for online assignments and the challenges of finding the diameter of the disks. The discussion highlights the need to calculate the total charge from the number of electrons and the charge of an electron. Overall, the participants are working through the equations to find the diameter of the disks while grappling with the complexities of the topic.
megr_ftw
Messages
68
Reaction score
0

Homework Statement



Two circular disks spaced 0.50 mm apart form a parallel-plate capacitor. Transferring 1.8*10^9 electrons from one disk to the other causes the electric field strength to be 1.3* 10^5 N/C. What are the diameters of the disks?

Homework Equations



F=k(q1)(q2)/r^2
E_capacitor= Q/(epsilon_0)*A


The Attempt at a Solution

 
Physics news on Phys.org
Look at your second equation. What can you find from it?
 
I'm doing the same problem.

All I can find from the second equation is that Q = Epsilon * A * E

Which doesn't really help because even if I break down A into pi * r^2 I still don't know r.. because if I knew r I would know d, which is what we're looking for.

I don't get how that helps.
 
Well I have another equation I was solving for earlier.

r = sqrt(Q/pi*eta)

I suppose I could substitute that into the equation set equal to Q and solve for Q.



Then maybe I could plug that Q from Q=Epsilon*A*E into the r = sqrt(Q/pi*eta) equation to find r.


Hmm. I can't stand this because of the precision required for these stupid online assignments, I get zero credit or full credit, none in between. Rewarded none for the effort I've put forth the same as someone who did nothing.

Oh well, computers give grades.
 
And now I end up with



Q=(Epsilon*E*Q) / eta



that makes no sense because if I go any further the Q's will cancel out *sigh*.. so I know I did something wrong.


Back to the drawing board.
 
Look at your second equation.

You know Q, you know ε0 and you know E. Can you find A? Once you know A can you find the diameter?
 
Last edited:
What is Q?

N electrons * Charge of electron?

I'm going back and re-reading the entire chapter leading up to this one in cased I missed something.

I'm completely lost when it comes to electricity and that's not like me.
 
thanks for the help. now if only webassign would stop lagging all the time and I could see if my answer is correct or not...
 
myxomatosii said:
What is Q?

N electrons * Charge of electron?

I'm going back and re-reading the entire chapter leading up to this one in cased I missed something.

I'm completely lost when it comes to electricity and that's not like me.

Yes, Q is the total charge of the N electrons.
 
Back
Top