Capacitance of a capacitor with dielectric of variable dimensions and constant volume

In summary: A(h,w)=-4h^2But I couldn't find a function that fit the data well, so I came up with another equation:A(h,w)=-\frac{1}{2}\int_{-L}^{L}\cdot\vec{\mathbf{x}}\,d\vec{\mathbf{x}}This equation fit the data much better, and it doesn't have any radical terms like the previous equation did. So I'm thinking that the area is a function of h and w, and it is described by:A(h,w)=-\frac{1}{2}\int_{-L}^{L}\
  • #1
MetalManuel
39
0

Homework Statement


ngrszs.png


Homework Equations


[itex]\int\vec{E}\cdot\vec{dA}=\frac{Q_{enc}}{\epsilon_{0}}[/itex]
[itex]\int\vec{E}\cdot\vec{dA}=\frac{Q_{enc}}{k\epsilon_{0}}[/itex]
[itex]V=\int\vec{E}\cdot\vec{dS}[/itex]
[itex]C=\frac{q}{V}[/itex]
[itex]C_{eq}=C_{1}+C_{2}+...[/itex]
[itex]\frac{1}{C_{eq}}=\frac{1}{C_{1}}+\frac{1}{C_{2}}+...[/itex]


The Attempt at a Solution


I didn't want to do the calculations in itex because it would take forever, but this is what i have so far. I just did the integrations quickly and went straight to the point and put in the equations.
1zpqurl.jpg



With the answer that I get I can't seem to get the answer. I have spent a lot of hours on this problem and it took me a while to figure out the proper areas and dimensions, but even after all that I am stuck. What is my problem? I have a feeling it has to do with the 4h^2 (it's not the right dimensions for the dielectric area).

Thanks
 
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  • #2


The volume of the dielectric is L*L*L/2 and is a constant? Where do you use this fact? I apologize if the answer is obvious.
 
  • #3


Spinnor said:
The volume of the dielectric is L*L*L/2 and is a constant? Where do you use this fact? I apologize if the answer is obvious.

The volume of [itex]\frac{L^{3}}{2}[/itex] is the total volume of the dielectric, but you can change the dimensions of the dielectric as long as long as [itex]l=w[/itex]. For example, you can say that the dielectric is now [itex]\frac{L}{8}, 2L[/itex] and [itex]2L[/itex] because the volume is still the same. You have to account for all the possible shapes that this dielectric can take.

edit:Imagine there's a piece of clay in between the capacitors, this will be the dielectric. You can shape the clay however you want and it will still have constant volume, just different dimensions. In this case though the clay would have to be a cubic shape, the two dimensions equal to each other.
 
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  • #4


I think I have figured it out, my mind is racing. Will update if I figure it out.
 
  • #5


So i finally solved it, this is how I am feeling right now.
[PLAIN]http://r3dsky.com/wp-content/uploads/2011/04/1302819681876.jpg

This problem took me so long to figure out, I'm glad the torture is finally over.It says:
We know that the area is constant for the dielectric(for the square side, not the thickness, l=w). My initial thoughts of the area being 4h^2 was incorrect because h could be << than l and w, therefore I thought that the area could be described with a function:
4id2s6.jpg
 
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Related to Capacitance of a capacitor with dielectric of variable dimensions and constant volume

What is capacitance?

Capacitance is the ability of a capacitor to store electric charge.

How is capacitance calculated?

The capacitance of a capacitor is calculated by dividing the electric charge stored on one plate by the potential difference between the two plates.

What is the effect of a dielectric on capacitance?

A dielectric material placed between the plates of a capacitor increases the capacitance by reducing the electric field between the plates.

How does the capacitance change with variable dimensions of the dielectric?

As the dimensions of the dielectric material change, the capacitance also changes proportionally. A larger dielectric material will result in a higher capacitance, while a smaller dielectric material will result in a lower capacitance.

What is the relationship between capacitance and volume of a capacitor with a dielectric of constant volume?

The capacitance of a capacitor with a dielectric of constant volume is directly proportional to the volume of the dielectric material. This means that as the volume of the dielectric material increases, the capacitance also increases.

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