Initial Force on a Mobile Charge in Field of Fixed-Point Charges
This Demonstration shows the action of Coulomb's law in the field of several fixed-point charges. You can select the positions and charges of the source particles. When you click the "find initial electric force" button, the initial force on the mobile test charge (black disk) is shown as a vector representing its initial motion. After you vary the charges of any of the objects, click the "reset" button and click "find initial electric force." The results are expressed in terms of the Coulomb's law constant.
Coulomb's law states that , where is the magnitude of the electrostatic force between two charges of magnitude and , is the distance between them, and is Coulomb's constant (in the program, the results are left in terms of ).
 W. S. Harvie. "Charge, Electric Field" in AP Physics C Notes, Electromagnetism (Torrey Pines High School Physics). 1999 (Jan 14, 2015). teachers.sduhsd.net/tpscience/physics/notes/AP%20 Physics %20 C %20 Notes %20-%20 EM/1%20-%2032 %20 Charge,%20 ELectric %20 Field.pdf.
"Initial Force on a Mobile Charge in Field of Fixed-Point Charges"
Wolfram Demonstrations Project
Published: January 15 2015