Determining electric field using gauss's law--different distributions

In summary, the conversation discusses the use of Gauss's law to determine the electric field of four different distributions. The speaker is trying to determine which distributions can effectively use Gauss's law, and mentions that all four distributions have charges. They also mention the possibility of using Q/(A*electric constant) to calculate the electric field, but are unsure if they can use Gauss's law for all four distributions. The conversation also explores the concept of symmetry and how it relates to the use of Gauss's law. The speaker points out that distributions A and D may not be symmetric enough to use Gauss's law, while distributions B and C may be more suitable. The conversation ends with a prompt to explain how Gauss's law can be used in cases B
  • #1
Helenah
3
0
Homework Statement
We are supposed to determine which (if any) of the distributions will need to/could use Gauss's law to determine the electric field
Relevant Equations
flux = Q/electric constant = EA
Screen Shot 2021-03-18 at 11.41.03 PM.png

These are the 4 distributions shown, and I have to determine which two distributions (or none at all) can use Gauss's law to determine the electric field.

So electric flux = EA = Q/electric constant.

Since all of them have charges, I could do something like Q/(A*electric constant) to get the electric field—that's where I'm confused, because I think I could actually use Gauss's law on all four of them. The only other way I can think of is that Gauss's law is applied to surfaces so that probably excludes lines (A) and disks (D), which do not really have surface area.
Am I right in thinking so? Is there a better / correct way to get to the answer?
 
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  • #2
You perhaps need to think about how you would practically use Gauss's law to determine the electric field.

Hint: think about symmetry.
 
  • #3
@PeroK
Hmm. Distribution A could potentially be viewed as line of charge + imaginary cylinder to get some electric field, but the charges aren't symmetric and hence will not be able to use gauss's law (?).
I'm not sure where else it's not symmetric though.
 
  • #4
Helenah said:
@PeroK
Hmm. Distribution A could potentially be viewed as line of charge + imaginary cylinder to get some electric field, but the charges aren't symmetric and hence will not be able to use gauss's law (?).
I'm not sure where else it's not symmetric though.
The trick to use Gauss's law effectively is to have a surface across which the electric flux must be constant.

Your intuition is right that A and D are problematic and B and C are better. Can you explain more clearly how you do things in cases B and C?
 

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