Question

Two point charges, Q1 = -6.7 µC and Q2 = 1.2 µC are located between two oppositely charged parallel plates. The two charges are separated by a distance of x = 0.32 m. Assume that the electric field produced by the charged plates is uniform and equal to E = 75000 N/C. Calculate the net electrostatic force on Q1 and give its direction.

My solution:

ForceQ1 = Force P + Force Q2

Fp = EQ1
FQ2 =kQ1Q2/ x^2

= (75000 x -6.7 x 10^-6) + [9x10^9 x -6.7 µC x 1.2 µC]/ 0.32^2

FQ1 = 0.20N

but webassign says i'm wrong. Can someone help?

Answer 1

I do not see the geometry diagram. Are you sure you have the signs correct? Try subtracting instead of adding. That seems the most likely error. Your general idea is fine.

Answer 2

(75000*-6.7*10^-6)-(9*10^9*-6.7*10^-6*1.2*10^-6)/0.32^2