# Homework Help: Electric field calulation

1. Jan 25, 2006

### Lewis

I'm having trouble with the question included in the attachment, part B specifically. If anyone could start me off it would be a great help!

Also, my answer for part A is included if anyone would care to check it
-Note: Chances are it's wrong :rofl:​

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2. Jan 26, 2006

### Meir Achuz

I can't open your attachment. Why don't you cut and paste and put it in without the attachment?

3. Jan 26, 2006

### Lewis

4. Jan 26, 2006

### Meir Achuz

I think the easiest way to do (B) is:
1. Use the field of a ring to get the field a distance z from a disk of charge Q. Use dq=2pi r dr/(pi r^2 Q) and integrate r from 0 to R.
This should give E=(2Q/R^2)[1-z/sqrt{z^2+R^2}].
2. Integrate E for the disk the same way you must have done for E for the ring for the hollow cylinder.
Let me know if you want to know the answer.

5. Jan 28, 2006

### Lewis

Cool, I got it now.

Thanks man, and sorry for the slow reply.