Capacitor Voltage Homework: Vo(0), v(infinity), & R

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SUMMARY

The discussion focuses on solving a capacitor voltage homework problem involving the equations for voltage across a capacitor and the behavior of an inductor in a circuit. The user correctly identifies Vo(0) as 8V but is uncertain about the values of v(infinity) and the resistance R, which is determined to be 12 ohms. The user learns that when the switch is in position B, the 40k ohm resistor becomes irrelevant as it is open-circuited, and the potential v(infinity) can be found by analyzing the circuit without the capacitor. Additionally, the inductor current i(infinity) is confirmed to be zero at steady state once the switch is closed.

PREREQUISITES
  • Understanding of capacitor voltage equations, specifically v(t) = v(infinity) + [v(0) - v(infinity)]e^(-t/RC)
  • Knowledge of circuit analysis involving resistors in parallel and series configurations
  • Familiarity with inductor behavior in DC circuits, particularly at steady state
  • Ability to interpret circuit diagrams and analyze voltage and current across components
NEXT STEPS
  • Study the impact of open circuits on resistor behavior in capacitor circuits
  • Learn about the transient response of inductors in RL circuits
  • Explore the concept of steady state in electrical circuits and its implications for current and voltage
  • Review circuit analysis techniques for mixed components, including capacitors and inductors
USEFUL FOR

Students studying electrical engineering, particularly those focusing on circuit analysis and transient response of capacitors and inductors. This discussion is beneficial for anyone tackling similar homework problems or seeking to deepen their understanding of circuit behavior in steady state conditions.

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Homework Statement



http://postimg.org/image/4m0huqxpj/

Homework Equations



v(t)=v(infinity)+ [v(0) - v(infinity)]^e(-t/RC)

The Attempt at a Solution

I found Vo(0) to be 8V, but I'm not sure about about v(infinity) and R

If the switch is at B and the capacitor is an open circuit at steady state, then shouldn't the resistance be the addition of the parallel combination of 40k and 30k and the 20k
however, the solution for R is given as 12and for v(infinity), I don't know know what to do
 
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When the switch moves to position B the 40 k resistor will have one end open, so no current can flow through it and it will play no further role in the circuit.

For v, remove the capacitor from the circuit and determine the potential across the points where it was connected.
 
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gneill said:
When the switch moves to position B the 40 k resistor will have one end open, so no current can flow through it and it will play no further role in the circuit.

For v, remove the capacitor from the circuit and determine the potential across the points where it was connected.

thanks, I have another question

http://postimg.org/image/m6c1rf60h/

why is there no mention of i(infinity) for this?
is the current through the inductor zero at steady state with the switch closed?


i(t)=i(infinity)+ [i(0) - i(infinity)]^e(-Lt/R)
 
Last edited by a moderator:
The inductor current falls away, becoming 0 at t=∞

The switch directs to ground all current from the battery, so the battery has no influence over the inductor once the switch closes.
 
princejan7 said:
thanks, I have another question

http://postimg.org/image/m6c1rf60h/

why is there no mention of i(infinity) for this?
is the current through the inductor zero at steady state with the switch closed?


i(t)=i(infinity)+ [i(0) - i(infinity)]^e(-Lt/R)

For a NEW question, why not make a NEW thread? Did you solve the problem of the current thread?
 
Last edited by a moderator:

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