RC circuit and kirchoff's loop rule

Click For Summary
SUMMARY

The discussion focuses on analyzing an RC circuit using Kirchhoff's Loop Rule to solve Question 27. The correct answer is identified as A, despite initial confusion regarding the application of Kirchhoff's Loop Rule in the inner left loop. The key conclusion is that after a long time, the capacitor behaves as an open circuit due to its infinite impedance at DC, leading to the relationship Vc = Vb/2 and Q = C * Vb/2.

PREREQUISITES
  • Understanding of RC circuits and their behavior over time.
  • Familiarity with Kirchhoff's Loop Rule and its application in circuit analysis.
  • Knowledge of capacitor impedance in DC circuits.
  • Basic algebra for combining equations and solving for variables.
NEXT STEPS
  • Study the implications of capacitor behavior in DC circuits, focusing on infinite impedance.
  • Learn advanced applications of Kirchhoff's Loop Rule in complex circuits.
  • Explore the relationship between charge, voltage, and capacitance in RC circuits.
  • Investigate time constants in RC circuits and their effects on circuit behavior.
USEFUL FOR

Electrical engineering students, circuit designers, and anyone seeking to deepen their understanding of RC circuits and Kirchhoff's Loop Rule.

okgo
Messages
61
Reaction score
0
http://www.screencast.com/users/trinhn812/folders/Jing/media/de5edaba-e848-47f5-82b9-bd770b216e95

I need help with Question 27 specifically. The correct answer is A, but I don't understand why.

I thought it would be B according to Korkoff's Loop rule of the inner left loop, where current of inner left loop is 0 after switch is closed after a long time. So V(battery) - Q/C = 0 so V(battery) =Q/C
 
Physics news on Phys.org
Let's see here, it can't be a because the cap isn't in parallel with the battery. A capacitor has infinite impedance at DC, so after an infinite time it can be modeled as an open circuit.

So loop 1)
Vb-Vc-IR=0
Loop 2)
Vb-2IR=0

combine to get
Vb-Vc-Vb/2=0

so
Vc=Vb/2

Vc=Q/C

so Vb/2=Q/C

Q=C*Vb/2

Voila.
 

Similar threads

Is This a Series or Parallel Circuit?
  • · Replies 13 ·
Replies
13
Views
1K
Korkhoff's Loop Rule: Proving Current Ratios
  • · Replies 1 ·
Replies
1
Views
2K
Sign conventions for Kirchhoff's loop rule
  • · Replies 7 ·
Replies
7
Views
2K
Why can we add impedances in series?
  • · Replies 4 ·
Replies
4
Views
2K
Maximum charge on the plates of a capacitor
  • · Replies 2 ·
Replies
2
Views
2K
Finding the Current in a circuit
  • · Replies 6 ·
Replies
6
Views
3K
LRC circuit:what is the voltage of the capacitor when the generator is at maximum vol
  • · Replies 2 ·
Replies
2
Views
2K
How Do You Prove and Analyze RC Circuit Formulas?
  • · Replies 1 ·
Replies
1
Views
5K
Engineering Solve 2 Loop RC Circuit: Find Q(topen)
  • · Replies 8 ·
Replies
8
Views
4K
Undergrad Discharge in a DC RC circuit and Kirchhoff's Loop Rule
  • · Replies 9 ·
Replies
9
Views
4K