# Electric Field Uniform

1. Feb 8, 2015

### I-aM-Lost

1. The problem statement, all variables and given/known data

Electric field at a distance 'a' from the end of a solid uniform charge volume

dq = Pdv
dv = (pi)(y)(dy)
A = (pi)(y)
dE = f(dq)

2. Relevant equations

What is the starting integral

3. The attempt at a solution

limits from 0 to b

(k)(p)(pi)(y)(dy)
E = --------------------
(b+a-y)^2

2. Feb 8, 2015

### Staff: Mentor

You'll have to provide a better problem description than that if you want to receive any meaningful help. As it stands I can sort of understand that you want to integrate over a charge distribution and determine the resulting electric field at some point.

But I have no idea what the shape of the distribution is, so I can't check your setup in any way. Also, you didn't actually ask a question, merely presented some work.

3. Feb 8, 2015

### I-aM-Lost

Sorry I forgot to add all the question. Find the electric field at a distance 'a' from the end of a solid cone uniform charge volume. Derive the equation. I just am trying to find the integral i can derive the equation from there.

So the picture is a solid cone around the y axis. With the point 'a' a distance above the cone itself. Height of the cone is b

4. Feb 8, 2015

### Staff: Mentor

So this is a 3D problem? You'll have a triple integral to cover the volume if you want to do it all in one go. maybe choose cylindrical coordinates. Otherwise you might attack it as a stack of disks with a single integral, provided that you know the field from a uniformly charged disk...

5. Feb 8, 2015

### I-aM-Lost

Correct it is a 3d problem. I was going to try to do the problem as a stack of disks.

6. Feb 8, 2015

### Staff: Mentor

So where are you at with regards the field from a single disk? Have you derived an expression for the electric field on the axis of a charged disk?

7. Feb 8, 2015

### I-aM-Lost

This all i really have. I have really been challenged by this stuff lately

limits from 0 to b

(k)(p)(pi)(y)(dy)
E = --------------------
(b+a-y)^2

8. Feb 8, 2015

### Staff: Mentor

It would be better to write out your equations on a single line so that space preservation is not a concern. That or place your text inside code tags " [ code ] .... [ /code ] " (without the spaces inside the square brackets). Best of all learn to use Latex syntax and write your equations using it. For example:

$f(x) = \int_0^\pi \left( 3x^2 + 2x \right) dx$

As for your problem, you need to describe what it is you're doing in detail. What the variables are, what the integral you're describing is meant to sum. The electric field on the axis of a uniformly charged disk is not as simple as that of a point charge! Take a look at the Hyperphysics website entry.

9. Feb 8, 2015

### I-aM-Lost

$f(x) = \int_0^b\left( (k)(p)(pi-y)(dy) \right )$ all over (b+a-y)^2

I am trying to derive the electric field for a charge volume of a solid cone.

k = constant
pi-y = From Area of pix^2
p - rho
dy - because the cone is around the y axis
b - total length of cone
a - distance above cone

10. Feb 8, 2015

### Staff: Mentor

Sorry, I'm just not picking out the cone geometry or the field from a disc in that .

Did you take a look at he Hyperphysics link that I placed in my last post? You'll see that the field from a single disk is not simple, depending upon both distance and radius of the disk. You're wanting to sum a stack of these (so over their z variable, but you can change it to y for your setup. What's important is that you get the radius to vary with the height so that the stack forms a cone of the proper dimensions. You haven't mentioned the width of the base of your cone).