A circuit with capacitor and resistor

In summary: In practice, there will always be some resistance, making the process take time. However, this is still a valid approximation for simple circuits. In summary, this circuit behaves as if the capacitor has a constant change in charge, and the current through it can be calculated by taking the voltage across the capacitor divided by the resistor.
  • #1
jazzchan
27
0
A circuit with capacitor and resistor !

Dear all,

it is a simple electric circuit include one capacitor and one resistor in parallel. about 25V is provided. Then i assume I1 cross the capacitor and I2 cross the resistor. Therefore, when a capacitor has a constant change, can i assume the I1 current flowing to zero, then I2 is V=RI ??

thanks a lot !
 
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  • #2
It's kind of tricky, I'm going to do my best here but you might want to wait for another answer.

I think it depends on what you mean by "a capacitor has a constant change". If you mean that it's fully charged, then yes, the current through it would be zero. However it can mean that the capacitor is constantly charging and discharging at the same rate, so the charge of it stays the same but there is still current through it. I think the latter is what's happening in this case, since I don't see how a capacitor can be fully charged when it's connected in parallel with a battery and a resistor.
 
  • #3
jazzchan said:
it is a simple electric circuit include one capacitor and one resistor in parallel. about 25V is provided. Then i assume I1 cross the capacitor and I2 cross the resistor. Therefore, when a capacitor has a constant change, can i assume the I1 current flowing to zero, then I2 is V=RI ??
Yes.

One little nitpick on the phraseology: voltage is across, current goes through. This seems nitpicky, but it will probably help you understand circuits better if you are strict with it.

BTW, if you assume ideal components, then this situation obtains immediately, since an ideal capacitor would take 0 time to charge to any arbitrary voltage supplied directly from an ideal voltage source.
 
Last edited:
  • #4
turin said:
BTW, if you assume ideal components, then this situation obtains immediately, since an ideal capacitor would take 0 time to charge to any arbitrary voltage supplied directly from an ideal voltage source.

One caveat, this is a purely theoretical situation as there is no voltage source with zero internal resistance and infinite current to produce a charged capacitor instantaneously.
 

1. What is the purpose of a capacitor in a circuit?

A capacitor is used to store and release electrical energy in a circuit. It works by storing charge on its plates, which can then be released when needed to provide a burst of energy. This is useful for stabilizing a circuit's voltage or creating a time delay.

2. How does a capacitor affect the current in a circuit?

In a DC circuit, a capacitor initially acts as an open circuit, blocking current flow. However, as the capacitor becomes charged, it begins to act as a short circuit, allowing current to flow. In an AC circuit, a capacitor can also act as a frequency-dependent resistor, allowing higher frequencies to pass through while blocking lower frequencies.

3. What is the relationship between a capacitor's capacitance and the amount of charge it can store?

The capacitance of a capacitor is directly proportional to the amount of charge it can store. This means that a capacitor with a larger capacitance can store more charge than one with a smaller capacitance.

4. How does a capacitor affect the voltage in a circuit?

A capacitor can act as a voltage stabilizer by storing excess charge when the voltage increases and releasing it when the voltage decreases. This helps to smooth out any fluctuations in voltage and keep it at a constant level.

5. What is the time constant of a circuit with a capacitor and resistor?

The time constant of a circuit with a capacitor and resistor is the amount of time it takes for the capacitor to charge to 63.2% of its maximum charge. It is calculated by multiplying the resistance and capacitance values in the circuit.

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