Electric Fields


by stylez03
Tags: electric, fields
stylez03
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#1
Jan26-07, 10:07 AM
P: 139
1. The problem statement, all variables and given/known data
A very long, straight wire has charge per unit length 1.4710^10

At what distance from the wire is the electric field magnitude equal to 2.57 N/C


2. Relevant equations

E = lambda / (2*pi*E_o*r)

E_o = 8.85*10^-9


3. The attempt at a solution

2*pi*E_o*E / lambda = r

Is this correct so far?
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Kurdt
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#2
Jan26-07, 10:33 AM
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Looks fine you just need to plug the numbers in.
stylez03
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#3
Jan26-07, 02:21 PM
P: 139
r = 2*pi*(8.85*10^-9)*(2.57) / (1.47*10^-10)

I'm not sure if lambda is represented correctly and is E just 2.57 or should it be 10^(something)

Kurdt
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#4
Jan26-07, 02:39 PM
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Electric Fields


E will just be 2.57 as stated in the problem. Why are you worried about lambda?
stylez03
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#5
Jan26-07, 02:50 PM
P: 139
I wasn't sure if lambda = 1.47*10^-10
Kurdt
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#6
Jan26-07, 02:53 PM
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probably more likely to be x10-10 than the other way round.
stylez03
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#7
Jan26-07, 02:55 PM
P: 139
Quote Quote by Kurdt View Post
probably more likely to be x10-10 than the other way round.
Thats what I had before 1.47 x 10^-10
Kurdt
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#8
Jan26-07, 02:57 PM
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What is it in the question?
stylez03
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#9
Jan26-07, 02:59 PM
P: 139
Quote Quote by Kurdt View Post
What is it in the question?
The original question was if lambda = 1.47 x 10^-10.

You said yes, so I just wanted to make sure.
stylez03
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#10
Jan26-07, 03:02 PM
P: 139
2*pi*(8.85*10^-9)*(2.57) / (1.47*10^-10) = r

This evaluated to:
r = 972

The online program says I'm off by an additive constant??
Kurdt
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#11
Jan26-07, 03:16 PM
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I've just noticed you have E on top of the fraction and lambda below. You need to swap these two so the equation is:

[tex] r=\frac{2k\lambda}{E} [/tex]

Like I said in a previous thread, try manipulating equations with just their symbols until the very last moment. Its a lot easier to spot problems that way.

EDIT: Sorry [tex] k=\frac{1}{4\pi \epsilon_0} [/tex]
stylez03
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#12
Jan26-07, 03:27 PM
P: 139
2* (1/4*pi* 8.85*10^-9) * (1.47*10^-10) / 2.57

= 1.03×10−3

Still says I'm off by a additive constant.
Kurdt
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#13
Jan26-07, 03:30 PM
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I think you've made a mistake in the calculation as i get a different answer. Try it again you're 3 orders of magnitude out.
Kurdt
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#14
Jan26-07, 03:33 PM
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Where did you get that value of epsilon nought from? It should be: 8.85x10-12
stylez03
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#15
Jan26-07, 03:35 PM
P: 139
Quote Quote by Kurdt View Post
Where did you get that value of epsilon nought from? It should be: 8.85x10-12
I need to be more careful from paper to online input. I have so much scratch work, some how I changed the epsilon value =[
Kurdt
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#16
Jan26-07, 03:38 PM
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No problem. Try a bit of latex for your equations it should help in future to diagnose problems quicker

http://www.physicsforums.com/showthread.php?t=8997


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