Ok so I have this question:

Two point charges of charge -2 µC and -3 µC respectively are separated by a distance of 15 cm. Point X is positioned at an equal distance away from each of the charges.

    a. Determine the net electric field at X.
    b. Find the point of equilibrium between the charges.

I've started writing out the formula for the electric field from charge -2 µC to point X, but I'm just confused about how you are supposed to do it when you don't know the distance between the charge and point X (the r or d value in the formula).


1 Answer 1


Let call A and B the two charges. A and B are separated by a segment of 15 cms. You need to calculate the electric field in the point X. About point X, you only know that it is at equal distance from both charges.

Therefore you need to calculate electric field in all possible X points, which are all positioned along a line that: - Is perpendicular to the segment between A and B - Cuts this segment in two halves.

As it doesn't change the result, let say that A and B are placed along the x-axis (at this point I would prefer not having called X the point), and the line is along the y-axis.

The value of the magnetic field is therefore a function with y as independent variable.

point X is along the y-axis

  • \$\begingroup\$ We wary of doing homework for people here. Especially given that this person seems to have a fundamental problem with mathematics and the meaning of variables. Provide pointers, don't do solutions. \$\endgroup\$ Jun 1, 2016 at 15:12

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