Posted by **Filip** on Saturday, May 12, 2012 at 6:20am.

a charged particle is in point (2, 3, 8) and has a charge Q1 = 5x10-10C. Another particle is at (5,7,0) and has a charge Q2 = 3x10-10C. Calculate how much work needed to move the first particle to the point (0, -7.2) using the electric field

- Physics -
**drwls**, Saturday, May 12, 2012 at 7:10am
The initial distance between the particles is

Sqrt(9 + 16 +64) = sqrt89 = R1

The final distance between the particles is

Sqrt(25 +196 +4) = sqrt225 = 15 = R2

Calculate the change in potential energy

K Q1 Q2 (1/R1 - 1/R2)

K is the Coulomb constant

You need to state the units for position. Is it meters?

- Physics -
**Filip**, Saturday, May 12, 2012 at 8:40am
I need to calculate this using the integral formula which is: W = - ∫ F dl = - q ∫ E dl

Where E = 1 / 4piε0 * R(vector) / R^3

I am just confused in what E-field I have to use and do I need to calculate X,Y & Z separately??

- Physics -
**Filip**, Saturday, May 12, 2012 at 8:42am
And regarding the position of the charges it only says its positions in the room for example charge 1 is : (x,y,z) = (2,-3,8). But it should be in Meters if SI-unit is needed..

- Physics -
**drwls**, Saturday, May 12, 2012 at 10:02am
The method I described is a shortcut that will give the correct answer. If you are going to use F*dl integrals, you have to specify the path the moviong charge follows, not just the end points. Ultimately, the answer only depends upon how much the distance between the charges changes, and the productof the two charges.

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