El. An electron has a charge of -1.6 x 10-19 C. How many E9. A uniform electric field is directed upward and has a mag- electrons would be needed to produce a net charge of nitude of 20 N/C. What are the magnitude and direction of -4.8 X 10- C? the force on a charge of -5 C placed in this field? E2. Two identical brass balls mounted on wooden posts ini- E10. A test charge of +4 x 10- C experiences a downward tially have different amounts of charge, one +3 puC and the electrostatic force of 12 N when placed at a certain point in other +15 p.C. The balls are allowed to touch and then are space. What are the magnitude and direction of the electric separated again. What is the final charge on each ball? field at this point? E3. Two identical steel balls mounted on wooden posts initially E11. A +1.5 x 10-6 C test charge experiences forces from two have different amounts of charge, one + 12 pC and the other nearby charges: a 12-N force due east and an 8-N other -4 p.C. The balls are allowed to touch and then are force due west. What are the magnitude and direction of separated again. What is the final charge on each ball? the electric field at the location of the test charge? E4. Two charged particles exert an electrostatic force of 8 N on E12. A charge of -3 x 10 % C is placed at a point in space each other. What will the magnitude of the electrostatic where the electric field is directed toward the right and has force be if the distance between the two charges is reduced a magnitude of 8.5 X 10* N/C. What are the magnitude and to one-half of the original distance? direction of the electrostatic force on this charge? E5. Two charged particles exert an electrostatic force of 27 N E13. A charge of +0.25 C is moved from a position where the on each other. What will the magnitude of the force be if electric potential is 10 V to a position where the electric the distance between the two particles is increased to three potential is 60 V. What is the change in potential energy of times the original distance? the charge associated with this change in position? E6. Two positive charges, each of magnitude 4 X 10-6 C, are E14. Four coulombs of positive charge flow from the +6 V posi- located a distance of 10 cm from each other. tive terminal of a battery to the negative terminal at 0 V. What a. What is the magnitude of the force exerted on each charge? is the change in potential energy of the charge? b. On a drawing, indicate the directions of the forces act- E15. The potential energy of a +2 x 10- C charge decreases ing on each charge. from 0.06 J to 0.02 J when it is moved from point A to E7. A charge of +2 x 10- C is located 20 cm from a charge point B. What is the change in electric potential between of -4 X 10-6 C. these two points? a What is the magnitude of the force exerted on each charge? E16. The electric potential increases from 100 V to 500 V b. On a drawing, indicate the directions of the forces act- from the bottom plate to the top plate of a parallel-plate ing on each charge. capacitor. 8. An electron and a proton have charges of an equal magni- a. What is the magnitude of the change in potential energy tude but opposite sign of 1.6 X 10-19 C. If the electron and of a -5 X 10- C charge that is moved from the bot- proton in a hydrogen atom are separated by a distance of tom plate to the top plate? 5 X 10-1 m, what are the magnitude and direction of the b. Does the potential energy increase or decrease in this electrostatic force exerted on the electron by the proton? process