A 1.95-nC charged particle located at the origin is separated by a distance of 0.0800 m from a 3.78-nC charged particle located farther along the positive x axis. Both particles are held at their locations by an external agent.

(a) What is the electrostatic force on the 3.78-nC particle?
(b) What is the electrostatic force on the 1.95-nC particle?

(a) The electrostatic force on the 3.78-nC particle is along the  

    positive x axis.

(b) The electrostatic force on the 1.95-nC particle is along the  

    negative x axis.

Explanation:

a.) The electrostatic force on the 3.78 nC particle is

       where is the 1.95 nC charge at the origin, and

                                        is the 3.78 nC  charge at 0.08 m from the origin

                                         r is the distance of 0.08 between the charges

                                          is the relative permittivity of 8.854 × .

Therefore in the positive x direction.

b.) The electrostatic force on the 1.95 nC particle is the same as the electrostatic force on the 3.78 nC particle except that its direction is in the negative x- axis direction.