# RC Circuit - Post-Lab Questions

• chrisfnet
In summary, the first problem involves finding the voltage across a capacitor after charging from zero voltage for two time constants and after discharging from a fully charged condition. The equations for each scenario are given, but there is confusion about setting VMaximum to 0 and the need for VBattery. For the second problem, the question asks how many time constants it takes for a capacitor in an RC circuit to discharge to less than 1% of its initial voltage. The equation for this situation is provided and the solution is found to be approximately 4.61 time constants. However, there is uncertainty about whether a symbolic answer such as ".5V" is desired and about the availability of necessary information.

## Homework Statement

What is the voltage across a capacitor after a time of two constants when charging from zero voltage. When discharging from a fully charged condition?

## Homework Equations

VCapacitor = VBattery(1 - e-t/2T)

VCapacitor = VMaximum * e-t/2T

## The Attempt at a Solution

I'm confused at how to start. I can do the algebra...

Charging from zero voltage - so would I set VMaximum to 0? Wouldn't I need to know VBattery? That wouldn't make sense to me. If I can get an idea of how to approach this problem, I should be able to solve it no problem. Thanks!

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## Homework Statement

With V = Vo*e-t/RC, it mathematically takes an infinite time for a capacitor in an RC circuit to discharge. Practically, how many time constants does it take for a capacitor to discharge to less than 1% of its initial voltage?

V = Vo*e-t/RC

## The Attempt at a Solution

0.01*Vo = Vo*e-t/RC
0.01 = e-t/RC
100 = et/RC
ln(100) = t/RC
2*ln(10)*RC = t

So, I'm saying that it takes approximately 4.61 time constants.

Would this be correct? Thanks!

For the first problem, I think your teacher wants a symbolic answer such as ".5V"

Your 4.61 time constants is right.

I'm not even sure how to work either of the first two problems? It seems like I should need to know more information...

Anyone? I've been trying to work the first two still, and I just can't get past the fact that I think that I need more information.

## 1. What is an RC circuit?

An RC circuit is an electrical circuit that contains a resistor (R) and a capacitor (C) connected in series. It is used to control the flow of electric current and store electrical energy.

## 2. What is the purpose of an RC circuit?

The purpose of an RC circuit is to control the flow of electric current and store electrical energy. It can be used in a variety of applications, such as filtering, frequency modulation, and timing circuits.

## 3. How does an RC circuit work?

An RC circuit works by using the resistor to control the flow of electric current and the capacitor to store electrical energy. When a voltage is applied to the circuit, the capacitor charges and discharges, creating a time-varying voltage across the circuit.

## 4. What factors affect the behavior of an RC circuit?

There are several factors that can affect the behavior of an RC circuit, including the values of the resistor and capacitor, the applied voltage, and the frequency of the input signal. Additionally, the type of capacitor used and the temperature can also impact the circuit's behavior.

## 5. What is the time constant of an RC circuit?

The time constant of an RC circuit is a measure of how quickly the capacitor charges and discharges. It is calculated by multiplying the resistance (R) and capacitance (C) values together. A larger time constant indicates a slower charging and discharging process, while a smaller time constant indicates a faster process.