Electric field calculation

  • Thread starter madah12
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  • #1
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Homework Statement



let say we have a positively charged rod with length L then what is the electrical field at the middle point of the rod


Homework Equations





The Attempt at a Solution


I put the origin at the middle point
so dE=Kdq/r^2, dq = Q/L dx
E= kQ/L integral from -L/2 to L/2 (1/x^2)dx
=-KQ/L[2/L +2/L] =KQ/L (4/L) =-4KQ/L^2

well I expected it to be zero and it wasn't so should it be if so then what did I do wrong?
 

Answers and Replies

  • #2
jhae2.718
Gold Member
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The electric field is defined as [tex]\mathbf{E} = \displaystyle \lim_{q_0 \to 0} \frac{\mathbf{F}}{q_0}[/tex].

The r2 term in the expression for dE is the distance between some charge element dQ and this test charge q0. You didn't take this into account in your setup.
 
  • #3
326
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well my test charge q_0 is at the mid point of the rod and so is my origin so the distance between it and any other charge is x.
 

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