# Solving RC Circuit Questions: How to Find Charge/Current

• joedirt
In summary, the conversation is about a series RC circuit with a 550-µF capacitor and a 12-kOhm resistor connected to a 12-V battery. The question is asking for the charge on the capacitor and the current in the resistor after 3.0 seconds. The person asking the question is unsure of which equations to use, but they mention knowing about Kirchhoff's current laws. The other person suggests using Kirchhoff's loop rule to solve the problem.
joedirt
Circuits question!?

A series RC circuit consists of a 550-µF capacitor (initially uncharged) and a 12-kOhm resistor. The combination is connected across a 12-V battery; 3.0 s later, what is

(a) the charge on the capacitor,

(b) the current in the resistor?

I really just want to know what equations I need to use.. I'm sure I can work it out knowing the right way to do it.

What equations do you know that concern RC circuits, or circuits in general?

I don't know any that's way I'm asking for the equation/s. I know a little about the Kirchhoff's current laws.

That's fine, you can use Kirchoff's laws to solve the problem. How would you apply Kirchoff's loop rule to this circuit?

I can provide you with the necessary equations and steps to solve this RC circuit question. The equations we will be using are:

1. Q = CV, where Q is the charge on the capacitor, C is the capacitance, and V is the voltage across the capacitor.

2. I = V/R, where I is the current in the resistor, V is the voltage across the resistor, and R is the resistance.

To find the charge on the capacitor, we first need to calculate the voltage across the capacitor. Since the capacitor is connected to a 12-V battery, the voltage across it will also be 12 V. So, using the first equation, we can write:

Q = (550 µF)(12 V) = 6.6 mC

Therefore, after 3.0 seconds, the charge on the capacitor will be 6.6 mC.

To find the current in the resistor, we can use the second equation:

I = (12 V)/(12 kOhm) = 1 mA

So, after 3.0 seconds, the current in the resistor will be 1 mA.

I hope this helps you in solving the RC circuit question. Remember to always use the appropriate equations and units in your calculations. Good luck!

## 1. How do I find the total charge in an RC circuit?

To find the total charge in an RC circuit, you can use the equation Q = CV, where Q is the total charge, C is the capacitance of the capacitor, and V is the voltage across the capacitor. Make sure to use the correct units for capacitance (Farads) and voltage (Volts) to get the correct answer.

## 2. What is the equation for current in an RC circuit?

The equation for current in an RC circuit is I = I0e^(-t/RC), where I0 is the initial current, t is time, R is the resistance in the circuit, and C is the capacitance of the capacitor. This equation is based on the relationship between current and voltage in a capacitor, and can be used to find the current at any given time in the circuit.

## 3. How do I calculate the time constant in an RC circuit?

The time constant in an RC circuit can be calculated using the equation RC, where R is the resistance in the circuit and C is the capacitance of the capacitor. This value represents the time it takes for the capacitor to reach approximately 63% of its maximum charge or discharge.

## 4. Can I use Kirchhoff's laws to solve RC circuit questions?

Yes, Kirchhoff's laws (specifically Kirchhoff's loop rule and Kirchhoff's junction rule) can be used to solve RC circuit questions. These laws are based on the conservation of energy and charge, and can help you determine the relationships between voltage, current, and resistance in a circuit.

## 5. How do I handle complex RC circuit questions?

Complex RC circuit questions may involve multiple capacitors, resistors, and other components. To solve these questions, it is important to break down the circuit into smaller parts and use the equations and principles discussed above to solve for the total charge and current in each part. Then, you can combine the results to find the total charge and current in the entire circuit.

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