Capicatance & magnitude of capacitor

Click For Summary

Homework Help Overview

The discussion revolves around a spherical capacitor with inner radius a and outer radius b, filled with epoxy and connected to a voltage source V. Participants are exploring how to calculate the capacitance and the surface charge density of the outer shell.

Discussion Character

  • Exploratory, Conceptual clarification, Mathematical reasoning, Assumption checking

Approaches and Questions Raised

  • The original poster attempts to use the formula for capacitance but questions its applicability due to the absence of voltage and dielectric constant in the equation. They express uncertainty about how to incorporate these factors into their calculations. Other participants suggest that the original poster should clarify their attempts to facilitate assistance.

Discussion Status

The discussion is ongoing, with participants providing varying levels of guidance. Some suggest looking up additional resources for better understanding, while others express concern that the original poster may not have fully engaged with the relevant material. There is no explicit consensus on the best approach yet.

Contextual Notes

Participants note that the original poster has not attempted the second question regarding surface charge density, indicating a potential gap in understanding the relationship between capacitance and charge. There are also mentions of uncertainty regarding the dielectric constant values and their application in the calculations.

Alouette
Messages
35
Reaction score
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...
 
Physics news on Phys.org
First you show the attempt. Then only we will know how to help
 
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*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:
Do a web search on "spherical capacitor". The Hyperphysics site has some appropriate info.
 
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
 

Similar threads

Replies
3
Views
2K
Replies
4
Views
2K
Replies
5
Views
1K
  • · Replies 3 ·
Replies
3
Views
2K
Replies
9
Views
3K
  • · Replies 5 ·
Replies
5
Views
2K
  • · Replies 3 ·
Replies
3
Views
2K
  • · Replies 11 ·
Replies
11
Views
2K
  • · Replies 4 ·
Replies
4
Views
4K