• Support PF! Buy your school textbooks, materials and every day products Here!

Surface charge of a cube?

  • Thread starter Violagirl
  • Start date
  • #1
114
0

Homework Statement



A cube of side a has a cube of side a/2 centered within it. The inner cube has a total charge Q that is uniformly distributed over its surface. A) For the surface of the outer cube, find:

s E * dA

B) Is this sufficient information to find the electric fields at points on the surface of the outer cube? Explain.

Homework Equations



E = F/Q

(???)

Not sure with a cube otherwise.

The Attempt at a Solution



Not sure how to start it. Drew out diagram of situation. See attached document.
 

Attachments

Answers and Replies

  • #2
662
307
  • #3
114
0
Thanks for your response! Ok so looking at it again:

∫E * dA

Since E is a constant, it can be pulled out:

E ∫dA = (a) (a/2) = a2/2

If I'm doing this right, then I just need to find the integral of a2/2, right? So I would then get:

E * a2x/2

As for the second question, if the above is correct, I would say then you have enough information to find the electric field at points on other areas of the surface of the cube too then.
 
  • #4
662
307
Use the Gauss's law! It directly gives the required integral without any integration!
##\int E.dA=Q/ \epsilon##
I would say then you have enough information to find the electric field at points on other areas of the surface of the cube too then.
Note:-If all you have got is the electric flux through the surface you cannot find the electric field at all the points.
To do this you will have to integrate due to the lack of symmetry of the surface.
 
  • #5
114
0
Ok, that makes more sense since the outer surface is not symmetric as you said. You have to integrate at along different points to find each electric field. Thanks for your help with this problem!
 

Related Threads for: Surface charge of a cube?

Replies
1
Views
3K
  • Last Post
Replies
6
Views
10K
  • Last Post
Replies
1
Views
11K
  • Last Post
Replies
1
Views
15K
Replies
2
Views
3K
  • Last Post
Replies
17
Views
1K
  • Last Post
Replies
2
Views
3K
  • Last Post
Replies
1
Views
10K
Top