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Work required to move charge

  • Thread starter indie452
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  • #1
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Homework Statement



situation:
there are two charges (+q) one at one corner of an equilateral triangle the other at another corner. the triangle has sides length a.

what is the work required to bring another charge (+q) in from infinity to the other corner on the equilateral triangle.


The Attempt at a Solution



ok so i know dW = -dU = F.dl

i thought that maybe finding (F) at the corner that we are bringing the charge to may help...this is:
Fc [at corner] = q2 / 2*pi*epsilon*a2

then i could just integrate this over the distance i am moving it with respect to a...however i know that the one limit will be [tex]\infty[/tex] however i dont know what the other will be

thanks for any help
 
Last edited:

Answers and Replies

  • #2
LowlyPion
Homework Helper
3,090
4
Consider the Voltage at the point from each of the 2 other charges.

V = k*q / r

Since work = q*ΔV

and V = 0

Then

Work = q*ΣV
 
  • #3
124
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ok so
the E at the point is 2q / 4*pi*epsilon*a2
the V at the point is 2q / 4*pi*epsilon*a

so work to bring in point is = q(2q / 4*pi*epsilon*a) = q2 / 2*pi*epsilon*a
 
  • #4
LowlyPion
Homework Helper
3,090
4
ok so
the E at the point is 2q / 4*pi*epsilon*a2
the V at the point is 2q / 4*pi*epsilon*a

so work to bring in point is = q(2q / 4*pi*epsilon*a) = q2 / 2*pi*epsilon*a
Looks like it.

Though E is a vector, don't forget, and V is a scalar here. In your first equation then the E would need to be added as vectors. Whereas for V you are adding scalars.

http://hyperphysics.phy-astr.gsu.edu/hbase/electric/mulpoi.html#c1
 
  • #5
124
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ok thanks...:biggrin:
 

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