Two 10-cm-diameter charged disks face each other, 17 cm apart. The left disk is charged to +40 nC and the right disk is charged to -40 nC.
a)What is the electric field, both magnitude and direction, at the midpoint between the two disks?
b) What is the force on a -1.0 nC charge placed at the midpoint?
So I have been trying this problem for hours now and am already maxed out on tries for a. I know how to do b but need the answer for a to get b.
Up until now I have been using E=(charge density of disk)/2(epsilon naught) however I am thinking now that this equation is only used for finding the electric field of an infinitely charged plane. So what equation am I supposed to use instead?