• Support PF! Buy your school textbooks, materials and every day products Here!

Parallel plate capacitors

  • #1
438
0

Homework Statement


A capacitor C1 (the one on top in the diagram) of capacitance 4 mu F is charged until its charge is 200 mu C and another capacitor C2 (the one below) of capacitance 3 mu F is charged until its charge is 300 mu C . Then both capacitors are connected in the circuit as shown in the figure . What is the total enerygy loss in the capacitors ?


Homework Equations



E=1/2CV^2 or E=1/2 QV

The Attempt at a Solution



I an not sure its asking for energy loss as a whole or energy loss for each capacitors .

so i know how to calculate the energy stored in each capacitors using the formula , what should i do after that >
 

Attachments

Answers and Replies

  • #2
rl.bhat
Homework Helper
4,433
5
Find the common potential difference across the capacitors.
They are connected in parallel.
find the equivalent capacitor.
Find the final energy stored in the combination of the capacitors.
 
  • #3
438
0
Find the common potential difference across the capacitors.
They are connected in parallel.
find the equivalent capacitor.
Find the final energy stored in the combination of the capacitors.
ok let me try

the effective pd would be 100+50=150 V

Effective capacitance = 7 mu

energy loss = 1/2 x 7 mu x 150^2 = 0.07875 J ?

but the answer given is 0.002 J

btw , is energy stored in the capacitors the same as energy loss in the capacitors
 
  • #4
rl.bhat
Homework Helper
4,433
5
Common voltage V = (Q1 + Q2)/(C1 + C2)
 
  • #5
438
0
Common voltage V = (Q1 + Q2)/(C1 + C2)
thanks , so let me retry ,

E= Q^2/2C

=[(500 x 10^(-6))^2]/2(7 x 10^(-6))

=0.018 which is approximately 0.02 J

Am i correct nw ?
 
  • #6
rl.bhat
Homework Helper
4,433
5
That is correct.
 

Related Threads for: Parallel plate capacitors

  • Last Post
Replies
1
Views
2K
  • Last Post
Replies
4
Views
2K
  • Last Post
Replies
1
Views
3K
  • Last Post
Replies
5
Views
6K
  • Last Post
Replies
1
Views
2K
  • Last Post
Replies
2
Views
952
  • Last Post
Replies
0
Views
1K
  • Last Post
Replies
1
Views
1K
Top