How Long Does It Take for a Capacitor to Charge to 80% of Its Maximum Voltage?

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Homework Help Overview

The discussion revolves around determining the time it takes for a capacitor to charge to 80% of its maximum voltage. The context involves concepts from electrical circuits, specifically relating to capacitors and their charging behavior.

Discussion Character

  • Exploratory, Assumption checking, Problem interpretation

Approaches and Questions Raised

  • Participants explore the implications of the question's lack of specific details regarding the circuit configuration and components. There is discussion about the role of resistance in the charging process and the relevance of the time constant in calculating charging time.

Discussion Status

Participants are actively questioning the completeness of the problem statement and discussing the necessary information to provide a meaningful answer. Some suggest that the equation for capacitor charging could be applicable if more data were available, while others express uncertainty about the question's clarity.

Contextual Notes

There is a noted absence of specific parameters such as resistance or the time constant, which are typically required to solve the problem. Participants mention that the question may be incomplete as presented in the exam.

Cetullah
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My friends, it is probably an easy one, but I don't know it and I have an exam tomorrow :X

Homework Statement


How much time does it take for a capacitor to reach %80 of its max. potential difference?

Homework Equations



Thats the part I m needing.

The Attempt at a Solution




Thank you for your help!
 
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It depends on the charging circuit. If an ideal capacitor is attached to an ideal voltage source through a switch, when the switch is closed, the capacitor will charge instantaneously. Non-ideal devices will have some resistance which will affect the charging time.
 
Hmm... I have translated the question from my test completely, and there isn't any other information given. So, does it mean that the question is incomplete?
 
Cetullah said:
Hmm... I have translated the question from my test completely, and there isn't any other information given. So, does it mean that the question is incomplete?

As mentioned before, in real life, even if there are no components in the circuit but the capacitor, the circuit will always have some non-zero resistance. So, if you assume that the capacitor is charging through a resistor, you can then answer the question.

How long does it take for the capacitor to reach 80% of full charge in an *RC* circuit?
 
Hi Cetullah! :smile:
Cetullah said:
How much time does it take for a capacitor to reach %80 of its max. potential difference?

That's like asking "How long is a piece of string?" :confused:

You have to know something about the capacitor (and the circuit it's in) to answer that!

Are you sure a "time constant" isn't given?​
 
Hi tiny-tim :smile:

Yeah, that's a weird question, but that's what exactly writes on the paper.

Our teacher is a weird man anyways.

But I guess, if sufficient data were given, we would use the equation "Vc=V*(1-e^(-t/RC)), right?
 
Cetullah said:
Hi tiny-tim :smile:

Yeah, that's a weird question, but that's what exactly writes on the paper.

Our teacher is a weird man anyways.

But I guess, if sufficient data were given, we would use the equation "Vc=V*(1-e^(-t/RC)), right?

That equation seems about right. The question I asked you in my previous post still stands. There is not reason why you cannot express an answer in terms of the time constant.
 
i agree :smile:
 
Oh cepheid, so you advice me to substitute the "t" with something like "kRC"?

Edit: Did so, and found one of the answers on paper "1.6"
 

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