Finding energy stored in capacitors without solving for current

6 replies · 3K views · last reply
zorro
Messages
1,378
Reaction score
0

Homework Statement



Circuit schematic with a voltage source V on the left, resistors R1 = 12R, R3 = 6R and R2 = 6R, switches k1 to k4, and two capacitors C on the right side.


Long time after closing K1,k2 and k3 the energy stored in each capacitor is?


The Attempt at a Solution



My method is to find out an expression for the current through the capacitor (of net capacitance 2C) at any time t and use I = CdV/dt to find out V across it at t=inf.

However this method appears to be very long. Is there any shortcut?
 
Attachments
  • Circuit schematic with voltage source V on the left, resistors R1 = 12R, R2 = 6R and R3 = 6R, switches k1, k2, k3 and k4, and two capacitors C on the right branches.
    b1c9f72f-12f4-4c9b-8fb7-7a0d21d72779.jpg
    7.7 KB · Views: 637
Yes. At T=inf the current through the capacitors is zero.
 
Antiphon said:
Yes. At T=inf the current through the capacitors is zero.
Also notice: that will leave you with a fairly simple circuit. The capacitors in combination with R3 are in parallel with R2[/SUB, but the voltage drop across R3 is zero since there is no current through it.
 
So you mean voltage drop across any capacitor is V ?
 
Abdul Quadeer said:
So you mean voltage drop across any capacitor is V ?
No.

As t → ∞ :

The only current flowing is through R1 and R2.

What is the voltage drop across R2?
 
Abdul Quadeer said:
Its V/3
Thank you!
Correct !