Work required to separate parallel plate capacitors

In summary, the work required to separate the parallel plate capacitor with capacitance C, charged to a value q and then isolated, when the separation between the plates is tripled, is given by W=Q^2/3C. However, the correct formula for ΔU should be written as ΔU=1/2C2V2^2-1/2C1V1^2, with the new capacitance C2 substituted for all instances of C in the original formula.
  • #1
avolp
5
0

Homework Statement


A parallel plate capacitor with capacitance C is charged to a value q and then isolated. The separation between the plates is then tripled. What was the work required to separate the capacitors?

Homework Equations


U=1/2CV^2
Q=CV
C=ε0A/d

The Attempt at a Solution


W=ΔU=1/2C1V1^2-1/2C2V2^2
=1/2C*(Q/C)^2-1/2*(C/3)*(Q/C)^2
=Q^2/3C
I tried this but this wasn't the correct answer and I can't figure out why. Thank you in advance for the help
 
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  • #2
avolp said:

Homework Statement


A parallel plate capacitor with capacitance C is charged to a value q and then isolated. The separation between the plates is then tripled. What was the work required to separate the capacitors?

Homework Equations


U=1/2CV^2
Q=CV
C=ε0A/d

The Attempt at a Solution


W=ΔU=1/2C1V1^2-1/2C2V2^2
=1/2C*(Q/C)^2-1/2*(C/3)*(Q/C)^2
=Q^2/3C
I tried this but this wasn't the correct answer and I can't figure out why. Thank you in advance for the help

Hi avolp, welcome to Physics Forums.

When you write your formula for ΔU you want to take the final energy and subtract the initial energy. You've got them the other way around, so your answer will be the negative of the correct value.

When you write the energy for the capacitor with the plate separation increased by a factor of 3, be sure to substitute the new capacitance for all the instances of the capacitor value C.
 
Last edited:
  • #3
Oh okay. Now I understand. Thank you so much.
 

1. What is the formula for calculating the work required to separate parallel plate capacitors?

The formula for calculating the work required to separate parallel plate capacitors is W = 1/2*C*(V2^2-V1^2), where W is the work in Joules, C is the capacitance in Farads, V2 is the final voltage, and V1 is the initial voltage.

2. How is the work required to separate parallel plate capacitors related to the distance between the plates?

The work required to separate parallel plate capacitors is directly proportional to the distance between the plates. This means that as the distance between the plates increases, the work required to separate them also increases.

3. Can the work required to separate parallel plate capacitors be negative?

No, the work required to separate parallel plate capacitors cannot be negative. This is because negative work would mean that energy is being added to the system, which is not possible in this scenario.

4. How does the work required to separate parallel plate capacitors change if the capacitance is increased?

If the capacitance of the parallel plate capacitors is increased, the work required to separate them also increases. This is because capacitance is directly proportional to the amount of charge stored on the plates, and more charge requires more work to be separated.

5. Is the work required to separate parallel plate capacitors affected by the voltage applied?

Yes, the work required to separate parallel plate capacitors is affected by the voltage applied. The higher the voltage, the more work is required to separate the plates, as seen in the formula for calculating work.

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