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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

[tex]\oint\vec{E}d\vec{A}=EA=\frac{q_{enclosed}}{\epsilon_{0}}[/tex]

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

Why is this?

Thinking:

[tex]\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} [/tex]

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!

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

so knowing

[tex]\oint\vec{E}d\vec{A}=EA=\frac{q_{enclosed}}{\epsilon_{0}}[/tex]

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

Why is this?

Thinking:

[tex]\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} [/tex]

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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