Determining Current Direction in a Charging RC Circuit

In summary, when the switch is closed, current flows clockwise from the battery to resistor R1 and down through the switch. For the capacitor, it is fully charged when the switch is closed and then discharges through resistor R2. The direction of current for a charging capacitor is determined by the direction of the flow of charge, which is from the positive plate to the negative plate.
  • #1
jolly_math
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5
Homework Statement
In the diagram below, the switch S has been open for a long time. It is then suddenly closed. TakeEe = 10.0 V, R1 = 50.0 kΩ, R2 = 100 kΩ, and C = 10.0 µF. Let the switch be closed at t = 5.0 s. Determine the current in the switch as a function of time.
Relevant Equations
I(t) = -I/RC * e^(-t/RC)
1676229825417.png

After the switch is closed, current flows clockwise from the battery to resistor R1 and down through the switch.

I don't understand the reasoning for the following: the current from the capacitor flows counterclockwise and down through the switch to resistor R2. How do I determine the direction of current when a capacitor is charging? Thank you.
 
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  • #2
jolly_math said:
I don't understand the reasoning for the following: the current from the capacitor flows counterclockwise and down through the switch to resistor R2. How do I determine the direction of current when a capacitor is charging? Thank you.
This capacitor is fully charged when the switch is closed. At that point the battery is effectively disconnected from the capacitor and the capacitor discharges through ##R_2##. Are you asking about a different problem?
 
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FAQ: Determining Current Direction in a Charging RC Circuit

What is the current direction when charging an RC circuit?

The current direction in a charging RC circuit flows from the positive terminal of the power supply, through the resistor (R), and into the capacitor (C). This current direction causes the capacitor to accumulate positive charge on the plate connected to the resistor and negative charge on the plate connected to the ground or the negative terminal of the power supply.

How does the current change over time in a charging RC circuit?

In a charging RC circuit, the current is initially at its maximum value when the switch is first closed. As the capacitor charges, the current exponentially decreases over time, approaching zero as the capacitor becomes fully charged. The rate of this change is determined by the time constant of the circuit, which is the product of the resistance (R) and the capacitance (C).

What is the time constant in an RC circuit, and how does it affect current direction?

The time constant, denoted by the Greek letter tau (τ), is the product of the resistance (R) and the capacitance (C) in the circuit (τ = RC). It represents the time it takes for the current to decrease to approximately 37% of its initial value. The time constant affects how quickly the current decreases as the capacitor charges, but it does not change the direction of the current flow.

Can the current direction reverse in a charging RC circuit?

No, the current direction does not reverse in a charging RC circuit. The current always flows from the positive terminal of the power supply, through the resistor, and into the capacitor until the capacitor is fully charged. Once the capacitor is fully charged, the current ceases, but it does not reverse direction.

How can you determine the current direction using Kirchhoff's Voltage Law (KVL)?

Using Kirchhoff's Voltage Law (KVL), you can determine the current direction by analyzing the voltage drops around the loop of the RC circuit. According to KVL, the sum of the voltage drops around a closed loop must equal zero. Starting from the positive terminal of the power supply, the voltage drop across the resistor (IR) and the voltage across the capacitor (V_C) must sum to the supply voltage (V_s). The current direction is from the positive terminal, through the resistor, and into the capacitor, consistent with the voltage drops observed.

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