How Is Capacitance Calculated in a Charged Parallel-Plate Capacitor?

In summary, the capacitance of the parallel-plate capacitor is 100uC, determined by dividing the total transferred charge of 400uC by the potential difference of 4V. This is based on the equation C=Q/V, where Q is the charge of one plate. The use of Gauss' law can also help in understanding the charge distribution in this scenario.
  • #1
crossfacer
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Homework Statement


The two plates of a parallel-plate capacitor initially carry equal amount of positive charge. If some charges are transferred from one plate to another, the charges on the plates are respectively +900uC and +100uC. The potential difference across the plates becomes 4V. What is the capacitance of the capacitor?

Homework Equations



C=Q/V

The Attempt at a Solution


I just pick randomly pick +900uC instead of +100uC:
C=900/4=225uC

4. Then I check the answer:

Totally 400uC moves away from one to the metal plate and move to another plate, so:
C=400/4=100uC

According to what I have learn, Q is the charge of one of the metal plate. In here, why should I subsitute 400uC, the amount of charge that is transferred?
 
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  • #2
Consider the relative charge...

Have you met Gauss' law?
 
Last edited:
  • #3
I haven't heard about it before. I will try to learn it by myself. Thank you:rolleyes:
 

What is capacitance and how is it related to a capacitor?

Capacitance is a measure of a capacitor's ability to store electrical charge. It is directly proportional to the amount of charge a capacitor can hold for a given potential difference, or voltage.

What factors affect the capacitance of a capacitor?

The capacitance of a capacitor is affected by three main factors: the distance between the plates, the surface area of the plates, and the type of material used as the dielectric between the plates. A larger distance between plates, a larger surface area, and a higher dielectric constant will result in a higher capacitance.

How is capacitance measured?

Capacitance is typically measured using a capacitance meter or by calculating it using the formula C = Q/V, where C is capacitance, Q is charge, and V is voltage.

What is the unit of capacitance?

The unit of capacitance is the farad (F), named after the scientist Michael Faraday. One farad is equal to one coulomb of charge per volt of potential difference between the plates of a capacitor.

How does capacitance impact the behavior of a circuit?

Capacitance can affect the behavior of a circuit in several ways. It can store and release electrical energy, filter out certain frequencies, and create time delays. It can also impact the overall impedance of a circuit, influencing the flow of current.

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