Capacitors: [SOLVED] Clearing Up Confusion | Check Your Solution Here

[i_island0]

[SOLVED] capacitors yet another question - please help

Sir, I have uploaded my two questions along with my solution.
Can you just tell me if my solution is correct.
The link is:
http://img412.imageshack.us/my.php?image=capcitorsao1.jpg

 

[Shooting Star]

1. Wrong, for the same reason as mentioned in your other post.

2. Don't put finite charges on infinite plates. If you talk about infinite plates, then you have to talk of the surface charge density. I'll just assume that the plates are very big but finite. In fig 5, you've earthed the right plate only. But the total charge on the left plate has become less. How? Where did the rest of the charge on the left plate go?

 

[i_island0]

i was thinking that if i take the charge on the left plate, then due to that charge, their will exists electric field inside the conducting plate on the right. So through induction, i brought that charge on the left plate to the right and made it go to the earth. Am i thinking right?

 

[rl.bhat]

If you connect a number of capacitors in series across a voltage source, the outer most plates must have same charge.
So through induction, i brought that charge on the left plate to the right and made it go to the earth
By induction you cannot transfer the charges from one plate to the other.

 

[i_island0]

ok, then how do i talk about the charge that is left over on the plate which was not earthed. That will be creating electric field inside the plate that was earthed. instead of induction, can i say that it was charge rearrangement.
One more thing, on earthing, can i say that charge on the outer plate goes to the earth.

 

[rl.bhat]

In Q2,if the two plates are charged with q1 and q2 , each face of the plate will have q/2 charge. Total charge in each plate does not change with the presence of the other plate. Distribution of the charge may change. So the charge distribution shown by you is not correct.

 

[i_island0]

Yes, i calculated again. And i found the charges on the two plates as shown in the figure:

http://img205.imageshack.us/my.php?image=newyy7.jpg

Does this sound reasonable.

 

[rl.bhat]

Yes. It is fine.

 

[i_island0]

thx Sir
I have put another question also, regarding the two capacitors in series; with one capacitor having some initial charge. I am interested to find the charge on both capacitors as a function of time. But i am not able to write an equation that will give me final charge on both the capacitors as same.
Can you give some idea regarding that as how shall i proceed.

 

[Shooting Star]

That problem will be discussed, and is being discussed, in the other running thread. Don't post the same thing under various threads. It's a sure way of putting people off.

 

[i_island0]

ok ok .. sorry