A charge of +6.0 μC experiences a force of 2.0 mN in the +x-direction at a certain point in space. (a) What was the electric field there before the charge was placed there? (b) Describe the force a -2.0 μC charge would experience if it were used in place of the +6.0 μC charge. (Ans: (a) 0.33 kN/C in +x-direction; (b) 0.67 mN in -x-direction.