Finding the Thickness of Polystyrene in a Capacitor

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In summary, the conversation discusses the concept of capacitance and its relationship to voltage, current, and resistance in a capacitor. It also mentions the use of breakdown voltage and the importance of understanding the symbols and terms used in equations. Ultimately, the breakdown field and the polystyrene thickness are used to determine the breakdown voltage, which is the necessary working voltage for the capacitor.
  • #1
warnexus
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Homework Statement


capacitance.jpg

Homework Equations



Capacitance = k(epsilon zero) (Area) / (distance)

Length (thickness) = (Volt)(Area) / (Current * Resistivity)

The Attempt at a Solution



Given:

Capacitance : 480 * 10 ^ -12 Farad
Radius: 24 * 10 ^ - 2 m
Area: pi * r ^ 2
dielectric constant of polystyrene: 2.6
breakdown field(MV/m) : 25
Resistivity of Polystyrene : 10 ^ 15

distance = (2.6)(8.85 * 10 ^ -12) (3.14 * (24* 10 ^ -2) ^ 2) / (480 * 10 ^ -12)

however finding the distance does not seem to help me at all since the other equation do not involve distance

any guidance would help
 
Last edited:
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  • #2
warnexus said:
distance = (2.6)(8.85 * 10 ^ -12) (3.14 * (24* 10 ^ -2) ^ 2) / (480 * 10 ^ -12)

Hello. What distance does this represent physically?
 
  • #3
distance apart for two capacitors
 
  • #4
I guess you mean the distance between the two circular plates of the capacitor. (You only have one capacitor.)

But isn't this the same as the thickness of the polystyrene?
 
  • #5
oh so that's what they mean! now that I think about you have a point there. so length, spacing, distance,thickness are same ideas. thanks for the guidance
 
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  • #6
Yes. It's always important to know what the symbols in an equation represent.
 
  • #7
TSny said:
Yes. It's always important to know what the symbols in an equation represent.

I was wondering. I need to find voltage of the capacitor. I do not know the current.

resistance = (resistivity)(length)/(pi * (r)^ 2)

I wind up finding the resistance which turned out to be 4793.7 ohms or 4793 ohms

but current is still missing.

current = (voltage)/(resistance)

voltage = (dielectric constant)(epsilon zero) (Current)(Resistivity)/(Capacitance)

or

I could have found voltage a different way

voltage = (Charge)/(Capacitance)

but no information about what charge is within the capacitor
 
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  • #8
It's a capacitor; you do not want current.
What do you take the term 'breakdown voltage' to mean?
 
  • #9
haruspex said:
It's a capacitor; you do not want current.
What do you take the term 'breakdown voltage' to mean?

failure of an electrical circuit

well i did list the polystyrene breakdown field to be 25 * 10 ^ 6 V/m

oh now I get it! multiply the thickness by the breakdown voltage and viola working voltage. thanks haruspex!
 
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  • #10
warnexus said:
failure of an electrical circuit
But what specifically in relation to capacitors?
well i did list the polystyrene breakdown field to be 25 * 10 ^ 6 V/m
Yes, but you did not use it.
I know the electric field = (Volt)/(Area)
So what would the breakdown voltage be for this capacitor?
 
  • #11
haruspex said:
But what specifically in relation to capacitors?

Yes, but you did not use it.

So what would the breakdown voltage be for this capacitor?

failure of an electrical field from a capacitor

i modify the content of my previous post. the electric field equation Electrical Field = (Volt/Area) would not work. I just wind up using the answer I got for thickness and used it with the breakdown voltage and found voltage that way.
 
  • #12
warnexus said:
failure of an electrical field from a capacitor
No, it would be the capacitor passing a DC current, which it is not supposed to do.
I just wind up using the answer I got for thickness and used it with the breakdown voltage and found voltage that way.
Let's get the terminology right: you used the breakdown field and the polystyrene thickness to find the breakdown voltage, which is the 'working voltage' required, yes?
 

1. How is the thickness of polystyrene measured?

The thickness of polystyrene can be measured using a caliper or micrometer. These tools allow for precise measurements of the thickness of the material.

2. What is the unit of measurement for polystyrene thickness?

The unit of measurement for polystyrene thickness is usually in millimeters (mm) or micrometers (μm). However, it can also be measured in inches (in) or centimeters (cm).

3. Is there a standard thickness for polystyrene?

There is no specific standard thickness for polystyrene as it can vary depending on the manufacturer and intended use. However, common thicknesses range from 1 mm to 10 mm.

4. How does the thickness of polystyrene affect its properties?

The thickness of polystyrene can greatly affect its properties. Thicker polystyrene sheets are more rigid and have higher compressive strength, while thinner sheets are more flexible and have lower compressive strength.

5. How can I calculate the thickness of polystyrene needed for my project?

The thickness of polystyrene needed for a project depends on the specific application and the load it will be supporting. It is important to consult with a professional or refer to engineering tables to determine the appropriate thickness for your project.

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