
#1
Jan2607, 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 1.47×10^10 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? 



#2
Jan2607, 10:33 AM

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PF Gold
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Looks fine you just need to plug the numbers in.




#3
Jan2607, 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) 



#4
Jan2607, 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?




#5
Jan2607, 02:50 PM

P: 139

I wasn't sure if lambda = 1.47*10^10




#6
Jan2607, 02:53 PM

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probably more likely to be x10^{10} than the other way round.




#7
Jan2607, 02:55 PM

P: 139





#8
Jan2607, 02:57 PM

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What is it in the question?




#9
Jan2607, 02:59 PM

P: 139

You said yes, so I just wanted to make sure. 



#10
Jan2607, 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?? 



#11
Jan2607, 03:16 PM

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PF Gold
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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] 



#12
Jan2607, 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. 



#13
Jan2607, 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.




#14
Jan2607, 03:33 PM

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Where did you get that value of epsilon nought from? It should be: 8.85x10^{12}




#15
Jan2607, 03:35 PM

P: 139





#16
Jan2607, 03:38 PM

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PF Gold
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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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