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## Main Question or Discussion Point

Hello,

I was looking over my notes and I was trying to figure out when we integrate Q enclosed when Q = ρ*d(volume).

If there's one thing I've learned from physics II you only integrate when a field is non-uniform. I'm just wondering how we know when it's uniform (usually the problem will tell you but sometimes it doesn't).

In my notes for example, my professor did an example where we found

Why is it for that problem we integrated but when I look over one of our past problems we didn't integrate:

I was looking over my notes and I was trying to figure out when we integrate Q enclosed when Q = ρ*d(volume).

If there's one thing I've learned from physics II you only integrate when a field is non-uniform. I'm just wondering how we know when it's uniform (usually the problem will tell you but sometimes it doesn't).

In my notes for example, my professor did an example where we found

**Q enclosed of an insulated sphere with a radial charge density of ρ and radius a. It was surrounded by a thick conducting shell of inner radius b, outer radius c, and total charge Q.**We then were asked to find q where r is less than a. In this part, we integrated ρ*d(volume).Why is it for that problem we integrated but when I look over one of our past problems we didn't integrate:

**A plasma, a hot gas of positively-charged ions, is confined to a very long, thin conducting cylindrical shell of inner radius a and outer radius b. The plasma within this conducting tube has a uniform volume charge density ρ0. (a) In terms of the variables of the problem (e.g., ρ0, a, b, ǫ0, and r), what is the field in the plasma tube (r < a) at some distance r from the axial center of the plasma tube?****Please don't solve the problem unless you're bored and want to. I'm just trying to figure out why we integrate in the first problem but not the second.**

Lastly Thanks!

Really appreciate your help! :)Lastly Thanks!

Really appreciate your help! :)