PRACTICE EXERCISE 4.1 Point charges 5 nC and -2 nC are located at (2, 0, 4) and (-3, 0, 5), respectively. (a) Determine the force on a 1-nC point charge located at (1, -3, 7). (b) Find the electric field E at (1, -3, 7). - Answer: (a) -1.004a, 1.284a, + 1.4a, nN, - (b) 1.004a, 1.284a, +1.4a, V/m.