Capicatance & magnitude of capacitor

In summary, the conversation involves a question about the capacitance of a spherical capacitor with a filling of epoxy and connected to a battery. The equations used to find the capacitance are provided, but it is unclear which one is the correct one to use. Additionally, there is a question about the magnitude of the surface charge density on the outer shell, but the units of the answer are not specified and it is suggested to review the chapter before attempting the question.
  • #1
Alouette
35
0

Homework Statement


There's a spherical capacitor, inner radius a and outer radius b, with a filling in between of epoxy, and also connected to battery of voltage V. What is the capacitance?

Also, what is magnitude of surface charge density outer shell?

Homework Equations


For Q1
1)C=4∏ε0(ab/b-a)

2)C = Q/ΔV

3)C = κC0

For Q2
s=Q/4∏r2

The Attempt at a Solution


Used above equation, but it doesn't include any voltage V nor dialelectric constant κ. Are these the right equations?

Haven't attempted Q2 since it seems to require C/m2 as units for answer...
 
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  • #2
First you show the attempt. Then only we will know how to help
 
  • #3
Sure. Except I already did. I said I used C=4∏ε0(ab/b-a) but this gave me the wrong answer. I noticed that it didn't even used V or dialelectric constant κ, but I'm unable to find how these fit it. The only other equations I found involving them were equations 2) and 3).

C = Q/ΔV , this has V but I'm unsure how there's a change in V when they gave me just a constant voltage. Also there wasn't any charge in the question either...

C = κC0, I would have to use the equation 1) C and then multiply by epoxy constant, which I found to be either 3.9, 4.1, or 4.4, not sure which one but I was going to plug them into find out.
 
  • #4
4*π*k*ε/((1/a)-(1/b)), where k is 3.6 and ε is 8.85e-12

I don't understand where these equations come from...

the 4πε is from the charge of the sphere?

why the subtraction of inverses?

Not looking for a detailed lecture, just a simple explanation would do to better help me understand the process of arriving at this answer.
 
Last edited:
  • #5
Do a web search on "spherical capacitor". The Hyperphysics site has some appropriate info.
 
  • #6
seems to me that you are attempting the question without studying the chapter. You don't have a clear idea of what capacitor is. The question you have asked is quite very simple. I don't know how to help you with this question as it is only formula based. I would advice you to first go through the chapter once then only attempt the question
 

1. What is capacitance and magnitude of a capacitor?

Capacitance is the ability of a capacitor to store electrical charge when a voltage is applied. It is measured in Farads (F). The magnitude of a capacitor refers to the amount of capacitance it has and is determined by the physical characteristics of the capacitor, such as the distance between the plates and the type of dielectric material used.

2. How is capacitance and magnitude of a capacitor calculated?

The capacitance of a capacitor can be calculated by dividing the charge stored on the capacitor by the applied voltage. The magnitude of a capacitor can be calculated by multiplying the capacitance with the applied voltage.

3. What factors affect the capacitance and magnitude of a capacitor?

The distance between the plates, the area of the plates, and the type of dielectric material used are the main factors that affect the capacitance and magnitude of a capacitor. A larger distance and area between the plates will result in a higher capacitance, while a different dielectric material can impact the magnitude of the capacitor.

4. How does the capacitance and magnitude of a capacitor affect its performance?

A higher capacitance allows a capacitor to store more charge, which can result in a stronger and longer-lasting electrical signal. The magnitude of a capacitor determines how much voltage the capacitor can handle before breaking down. A higher magnitude allows for a higher voltage to be applied, making the capacitor more versatile in different circuits.

5. Can the capacitance and magnitude of a capacitor be changed?

The capacitance and magnitude of a capacitor can be altered by changing the physical characteristics of the capacitor, such as the distance between the plates or the type of dielectric material used. However, these changes can also affect the overall performance of the capacitor, so it is important to carefully consider the desired capacitance and magnitude before altering a capacitor's design.

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