# Quick Couple Concept Questions on Guass's Law

• godtripp

#### godtripp

Just a couple quick questions I was wondering about.

Also, this is an Introductory E&M class so we don't actually perform the surface integral

so knowing
$$\oint\vec{E}d\vec{A}=EA=\frac{q_{enclosed}}{\epsilon_{0}}$$

When using cylindrical symmetry I'm supposed to ignore any flux on the top and bottom ends.

Why is this?

Thinking:
$$\oint\vec{E}d\vec{A}= \oint\vec{E}d\vec{A}_{top} + \oint\vec{E}d\vec{A}_{bottom} + \oint\vec{E}d\vec{A}_{side}$$

Can I use guass' law to find the E-field and or flux of a small cylinder or disk?

Lastly, calculating the E field around a sphere some distance away turns out to be the same for an e field of a point charge.
From this the force of the sphere on a point charge would be the same as using coulombs law.

If I have large spheres, would each respective force be the same as using coulombs law (assuming the spheres are not very far away from each other) why or why not?

Thanks!

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