I am just very confsed about how to do these sort of questions where they give you a point in the middle of two charges. The farthest I've gotten in questions relating to coulomb's law, is using the formula \$F = {kq_1q_2 \over d^2}\$ to work out one of the unknowns when given two variables. Can someone please explain how you would do a question like this:

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.
  • \$\begingroup\$ Welcome to EE.SE! We do not give direct answers to "homework" questions, but we will offer guidance if you show enough of your work to demonstrate the specific point you're stuck on. To start with, do you understand how the field is distributed around a point charge? Do you understand how superposition can be used to find the combined field from multiple charges? \$\endgroup\$
    – Dave Tweed
    May 24, 2016 at 11:18
  • \$\begingroup\$ Here's a hint - electric field strength at a point is defined as the force experienced by a charged particle at that point in the field, divided by the value of the charge on the particle - that is electric field strength is force per unit charge. \$\endgroup\$
    – stefandz
    May 24, 2016 at 11:25

1 Answer 1


First of all, I would like to bring up the points that others have brought up, We cannot solve all of the question for you. You have to show some signs of trial and we will guide you from there on. With that being said, you have mentioned that you know how to find one of the variables from the equation: $$F={kq_1q_2\over r^2}$$ Now this equation on its own is not enough to solve this question as it enquires about electric field. I think you should read some about electric field wikipedia Now for the starters the relation between electric field and Force is given by: $$F=qE$$

Also the electric field follows the principle of superposition Wikipedia that is the resultant Electric field is the addition of electric field produced by all charges. Electric field also is a vector. Now using the above you can find the electric field at point X To find the equilibrium you just have to find the point in the electric field which experiences the same amount of force from both the directions.

PS : I think this question should be asked in the Physics stackexchange

  • 1
    \$\begingroup\$ @stefandz Thanks for the editing I was wondering how to get the r below everything. \$\endgroup\$ May 24, 2016 at 11:48

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