Understanding RC and RL circuits

  • Context: High School 
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Discussion Overview

The discussion centers around understanding the behavior of RC (resistor-capacitor) and RL (resistor-inductor) circuits, particularly focusing on the charging and discharging processes of capacitors and inductors at different time intervals after a switch is closed.

Discussion Character

  • Exploratory
  • Technical explanation
  • Conceptual clarification

Main Points Raised

  • One participant expresses difficulty in understanding the charging and discharging of RC and RL circuits, specifically the current and charge behavior at various times after the switch is closed.
  • Another participant suggests starting with capacitors, noting that they are generally easier to understand than inductors.
  • Resources such as Hyperphysics are mentioned as potentially helpful for understanding the charging of capacitors and transients in inductors.
  • A rule of thumb is presented, stating that at DC, a capacitor behaves as an open circuit while an inductor acts as a short circuit, and vice versa at very high frequencies.
  • The same participant explains that initially, when the switch is thrown, the capacitor acts as a short circuit, allowing current to flow according to Ohm's law, but eventually behaves as an open circuit, resulting in no current flow.

Areas of Agreement / Disagreement

Participants have not reached a consensus on the understanding of RC and RL circuits, and multiple viewpoints regarding the complexity of capacitors and inductors are present.

Contextual Notes

Some assumptions about the behavior of capacitors and inductors under different conditions are mentioned, but specific mathematical steps or definitions are not fully explored or resolved.

driedupfish
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Hi everyone. I am having trouble understanding RC AND RL circuits. Specifically the charging and discharging of circuits. The current and charge that goes through the inductor or capacitor at various time(At time=0 or some time after the switch is closed or a long time after the switch is closed).
Thanks
 
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Hi there! :smile:

I'm sorry to hear you're driedup … you need to get a nice little bowl like mine :wink:
driedupfish said:
Hi everyone. I am having trouble understanding RC AND RL circuits. Specifically the charging and discharging of circuits. The current and charge that goes through the inductor or capacitor at various time(At time=0 or some time after the switch is closed or a long time after the switch is closed).

Inductors are difficult. Capacitors are easier.

Concentrate on understanding the process with just a capacitor first.

See the PF Library or wikipedia …

what part is worrying you? :smile:
 
I usually just remember the following rule of thumb:

At DC a capacitor is an open circuit and an inductor is a short circuit.

The corolary is that for very high frequencies a capacitor is a short and an inductor is an open circuit.

So when you first throw the switch you apply the high-frequency corolary. The capacitor is a short so all of the voltage is across the resistor and the current is given by Ohm's law. After a while it settles down and you apply the DC rule. The capacitor is an open circuit so all the voltage is across it and there is no current.
 

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