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 Electricity and Magnetism Electricity and Magnetism Physics Help Forum Mar 17th 2010, 05:19 PM #1 Junior Member   Join Date: Mar 2010 Posts: 11 Uniform line charge of linear charge density + E field A uniform line charge of linear charge density 9.0 nC/m extends from x=1m to x=5m. What is the total charge on the line?   Mar 17th 2010, 05:30 PM   #2
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 Originally Posted by chevy900ss A uniform line charge of linear charge density 9.0 nC/m extends from x=1m to x=5m. What is the total charge on the line?
Hey chevy900ss, welcome to PHF!
The answer is pretty straightforward. What's your attempt? A charge density of 9.0 nC/m means that in one meter you have 9.0 nC. How many meters do you have from x=1m to x=5m? Thus the result is...?
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Isaac
If the problem is too hard just let the Universe solve it.   Mar 17th 2010, 05:33 PM #3 Junior Member   Join Date: Mar 2010 Posts: 11 5m-1m=4m 4x9= 36nC Is this right? Last edited by chevy900ss; Mar 17th 2010 at 05:36 PM.   Mar 17th 2010, 05:38 PM   #4
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 Originally Posted by chevy900ss 5m-1m=4m 4x9= 36nC Is this right?
Yes. __________________
Isaac
If the problem is too hard just let the Universe solve it.   Mar 17th 2010, 05:39 PM #5 Junior Member   Join Date: Mar 2010 Posts: 11 Ok how do i figure out what the electric field is at x=10m? Would i use the formula: E= (1/4 x pi x enot)(q/r^2) Last edited by chevy900ss; Mar 17th 2010 at 05:49 PM.   Mar 17th 2010, 06:03 PM   #6
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 Originally Posted by chevy900ss Ok how do i figure out what the electric field is at x=10m? Would i use the formula: E= (1/4 x pi x enot)(q/r^2)
In future please create a new thread for each new question.

You have to do an integration. What is the electric field due to a dx element situated at x meters from the point considered? Remember that the E field is a vector field and hence have a direction.
By the way, I don't understand your notation... what is "enot"?
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Isaac
If the problem is too hard just let the Universe solve it.   Mar 17th 2010, 06:10 PM #7 Junior Member   Join Date: Mar 2010 Posts: 11 enot = 8.85x10^-12 C^2/Nm^2   Mar 17th 2010, 06:17 PM #8 Junior Member   Join Date: Mar 2010 Posts: 11 Im still confused on how to integrate.   Mar 17th 2010, 06:18 PM   #9
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 Originally Posted by chevy900ss enot = 8.85x10^-12 C^2/Nm^2
Ok, then no... the formula you wrote is not the good one.
What r would you choose?
Instead, dE=(kdQ)/r³ r where the bold letters represent vectors.
You have to integrate dE from r=5 to r=9. (why? Because r=9 is the distance between x=10m to x=1m and r=5 is the distance between x=5 to x=10.)
I'll help you a bit more... what is dQ, that is, the charge of a very small (differential in fact, of length dx) element of the charged line?
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Isaac
If the problem is too hard just let the Universe solve it.   Mar 17th 2010, 06:32 PM #10 Junior Member   Join Date: Mar 2010 Posts: 11 i understand where r=5 and r=9 comes from, and know k= 9x10^9Nm^2/C^2. For some reason though i cant seem to realize what value dQ is. Q is 9.0 nC/m right.  Tags charge, density, field, line, linear, uniform Thread Tools Show Printable Version Email this Page Display Modes Linear Mode Switch to Hybrid Mode Switch to Threaded Mode Similar Physics Forum Discussions Thread Thread Starter Forum Replies Last Post Tutan Electricity and Magnetism 2 Dec 1st 2015 08:40 AM Frostking Electricity and Magnetism 1 Jun 7th 2011 08:07 PM ambrja86 Electricity and Magnetism 6 Oct 4th 2010 10:51 AM dspaulding09 Electricity and Magnetism 1 Feb 24th 2010 06:59 PM reverseswing Advanced Electricity and Magnetism 0 Jun 19th 2009 02:02 AM 