RC Circuit: Effects of Increasing R on E and V

In summary, the conversation discusses the behavior of an RC circuit when the value of R is increased. It is mentioned that RC is the time constant, but it is not the time it takes for the voltage across R to reach half its initial value. The time for it to reach half is 0.693RC or ln2 x RC. It is also explained that measuring this time from an oscilloscope can help calculate RC. The conversation also mentions that the voltage across R will decrease exponentially from the battery voltage, and when it reaches half, the time taken is 0.693RC. An example is given of a 1 microfarad capacitor and 1 megohm resistor, where the time constant is 1
  • #1
M. next
382
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
 
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  • #2
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 !
 
  • #3
I donno why it is not uploading :/!
Concerning the tau, please elaborate supposing you can imagine an oscilloscope signal..
 
  • #4
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
 
  • #5
Thank you very much truesearch
 

1. What is an RC circuit?

An RC circuit is a type of electrical circuit that consists of a resistor (R) and a capacitor (C) connected in series. This circuit is commonly used to control the flow of electric current and can be found in various electronic devices.

2. How does increasing the value of R affect E and V in an RC circuit?

Increasing the value of R in an RC circuit will cause a decrease in the voltage (V) across the resistor and an increase in the voltage (E) across the capacitor. This is because the capacitor will take longer to charge, resulting in a higher voltage across it.

3. What is the significance of R in an RC circuit?

The resistor (R) in an RC circuit helps to control the flow of current and determines the time constant of the circuit. A higher value of R will result in a longer time constant, meaning it will take longer for the capacitor to charge or discharge.

4. How does changing the value of R affect the time constant of an RC circuit?

Changing the value of R in an RC circuit will directly affect the time constant of the circuit. A higher value of R will result in a longer time constant, while a lower value of R will result in a shorter time constant. This means that the capacitor will take longer to charge or discharge with a higher value of R.

5. What are the practical implications of increasing R in an RC circuit?

Increasing the value of R in an RC circuit can have practical implications such as slowing down the response of the circuit and reducing the amount of current flowing through it. This can be useful in certain applications, such as in filters and delay circuits.

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