RC Circuit: Effects of Increasing R on E and V

Click For Summary

Discussion Overview

The discussion revolves around the effects of increasing resistance (R) in an RC circuit on the voltages across the capacitor (V(capacitor)) and the resistor (V(resistor)), as well as the measurement of the time constant (tau) using an oscilloscope. Participants explore the implications of these changes on the circuit's behavior and clarify the definition of tau.

Discussion Character

  • Technical explanation
  • Conceptual clarification
  • Debate/contested

Main Points Raised

  • One participant questions the effects of increasing R on the visualized signals of E, V(capacitor), and V(resistor).
  • Another participant clarifies that tau (the time constant) is not the time taken for the voltage across the resistor to reach half its initial value, but rather that this time is 0.693RC.
  • A participant suggests that measuring the time for V(resistor) to decrease to half using an oscilloscope can help calculate RC.
  • There is a description of the behavior of current and voltage in the circuit when the switch is closed, noting that current starts at a maximum and decreases exponentially.
  • One participant provides an example with specific values (1 microfarad and 1 megohm) to illustrate the time constant and the time taken for the voltage across R to halve.

Areas of Agreement / Disagreement

Participants express some agreement on the definition of tau and its relation to the voltage across the resistor, but there is uncertainty regarding the implications of increasing R and how it affects the circuit's behavior. The discussion remains unresolved on the broader effects of increasing resistance.

Contextual Notes

There are limitations in the discussion regarding the assumptions made about the circuit's behavior as R increases, and the exact nature of the visualized signals is not fully defined. The dependence on the specific values of R and C is also not explored in detail.

Who May Find This Useful

This discussion may be of interest to students and enthusiasts of electrical engineering, particularly those studying RC circuits and time constants, as well as individuals looking to understand oscilloscope measurements in circuit analysis.

M. next
Messages
380
Reaction score
0
Supposing we have an RC circuit (see figure)
As we increase R, what will happen to the visualized signal of E and V(capacitor) and V(resistor)?


And a general question about measuring the (Tao) [the one that equals to RC] BUT FROM THE OSCILLOSCOPE..

They mentioned it is the time for which V(resistor) decreases to half its initial value (but I still don't get it)

Thanks in advance
 
Engineering news on Phys.org
Hi M.next... I cannot see your diagram ! (I can picture what you mean but...)
One thing to note... RC is called the time constant (tau) but this is NOT the time taken for the voltage across R to 1/2.
The time for it to 1/2 is 0.693RC (ln2 x RC) so measuring the time to become 1/2 from the oscilloscope (not difficult !) enables you to calculate RC
Hope this helps... your diagram would be useful !
 
I donno why it is not uploading :/!
Concerning the tau, please elaborate supposing you can imagine an oscilloscope signal..
 
If you have a simple R in series with a C connected to a battery of voltage E...then when the switch is closed the current will be a max (= E/R) and will decrease exponentially. The voltage across R will also decrease exponentially from a value of E.
When the voltage across R has decreased to E/2 then the time taken = 0.693RC.
If you can display the V across R on a CRO you should be able to measure the time for V to become V/2.
I am not certain what you mean by...'as we increase R...!
Hope this helps.
As an example: if you have 1 microfarad in series with 1 megohm then time constant = 1 second so it will take 0.693s for the voltage across R to become 1/2
 
Thank you very much truesearch
 

Similar threads

  • · Replies 6 ·
Replies
6
Views
8K
  • · Replies 41 ·
2
Replies
41
Views
8K
Replies
3
Views
4K
  • · Replies 12 ·
Replies
12
Views
4K
  • · Replies 27 ·
Replies
27
Views
3K
Replies
5
Views
3K
Replies
33
Views
7K
  • · Replies 4 ·
Replies
4
Views
2K
  • · Replies 2 ·
Replies
2
Views
3K
Replies
2
Views
3K