# RC Circuits and maximum voltage calculation

• snoweangel27
In summary, the first question involves calculating the maximum voltage across a capacitor given the charge on a battery and the capacitance. The maximum voltage is equal to the voltage of the battery. The second question involves finding the current in R immediately after the switch is closed in a circuit with a 12V potential drop across the capacitor and a 36V battery. Kirchhoff's Law can be applied to solve for the current, but the answer may not be correct.
snoweangel27
[SOLVED] RC Circuits

## Homework Statement

1. I have two questions in regards to RC circuits, the first one is how to calculate the maximum voltage across a capacitor, knowing the charge on a battery and the capacitance.

2. The other question involves this circuit

where the potential drop across the capacitor is 12V and the Battery is 36 V. R and C are also known. I need to calculate the current in R immediately after the switch is closed.

## Homework Equations

For the first problem I am sure I am just overlooking something. As far as I know I can't use the equation V = Q/C as that will just give me the Voltage of the battery.

## The Attempt at a Solution

In the second problem, I applied Kirchhoff's Law to obtain -I(1)*R(1)-12V+36V=0, where I then solve for I(1), but my answer in not correct, and I am not sure what I am doing wrong.

For the first problem, the maximum voltage across a capacitor is equal to the voltage of the battery. So if the battery has a voltage of V, then the maximum voltage across the capacitor is also V.

1. To calculate the maximum voltage across a capacitor in an RC circuit, you can use the equation Vmax = Q/C, where Vmax is the maximum voltage, Q is the charge on the capacitor, and C is the capacitance. This equation shows that the maximum voltage is directly proportional to the charge and inversely proportional to the capacitance. Therefore, if you know the charge and capacitance, you can easily calculate the maximum voltage.

2. For the second problem, your approach using Kirchhoff's Law is correct. However, make sure that you are using the correct values for the resistance and voltage in your equation. Also, remember to take into account the direction of the current when applying Kirchhoff's Law. If your answer is still not correct, double check your calculations and equations to make sure there are no errors.

## 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 or parallel. These circuits are commonly used in electronic devices and can have various applications such as filtering, timing, and signal processing.

## 2. How do you calculate the maximum voltage in an RC circuit?

The maximum voltage in an RC circuit can be calculated using the formula Vmax = E(1 - e^(-t/RC)), where E is the initial voltage, t is the time, R is the resistance, and C is the capacitance. This equation is derived from the charging or discharging equation for a capacitor, which is Q = Qmax(1 - e^(-t/RC)).

## 3. What is the time constant of an RC circuit and how do you calculate it?

The time constant of an RC circuit is a measure of how quickly the capacitor charges or discharges. It is calculated by multiplying the resistance (R) and capacitance (C) of the circuit, represented by the symbol τ = RC. It is also equal to the time it takes for the capacitor to charge to 63.2% of its maximum voltage.

## 4. How does the value of the resistor and capacitor affect the maximum voltage in an RC circuit?

The value of the resistor and capacitor in an RC circuit affects the maximum voltage in two ways. First, a higher resistance will result in a longer charging time, and therefore a lower maximum voltage. Second, a higher capacitance will result in a longer discharging time, and therefore a higher maximum voltage. In general, increasing the resistance will decrease the maximum voltage, while increasing the capacitance will increase the maximum voltage.

## 5. How does the time constant of an RC circuit affect the maximum voltage?

The time constant of an RC circuit is directly related to the maximum voltage. A longer time constant means the capacitor takes longer to charge or discharge, resulting in a higher maximum voltage. Conversely, a shorter time constant means the capacitor charges or discharges more quickly, resulting in a lower maximum voltage.

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