Question

Three 10-cm-long rods form an equilateral triangle. Two of the rods are charged to + 19 nC, the third to - 19 nC.What is the electric field strength at the center of the triangle?

Answer 1

We calculate the electric field as follows:
r = √(3)/6 x 19 cm = .05484 m 
The angle for the triangle would be 30 on each side.
tan(30) = r/(L/2) 

E' = kQ/{r*sqrt[(L/2)^2 + r^2]} = (8.99e9 x 15e-9) / {.05484 * sqrt[(.19/2)^2 + .003]}
E' = 22413 N/C
The value above is the electric field strength for a single rod at the center. 

|E'| = 22413 N/C 
E = 2|E'|sin(30) + |E'| = 49000 N/C