Q1=-q2=q3=2.10^-8 đặt tại A, B,C .tìm lực điện tổng hợp tác dụng lên q4=2.10^-8 đặt tại D sao cho ANCD là hình a, vuông vs a= 2cm
b, chữ nhật vs a=4cm, b= 2cm

Athin nonconducting rod with a uniform distribution of positive charge q is bent into a circle of radius r. the central perpendicular axis through the ring is a z-axis, with the origin at the center of the ring. a) what is the magnitude of the electric field due to the rod at z = 0? n/c (b) what is the magnitude of the electric field due to the rod at z = infinity? n/c (c) in terms of r, at what positive value of z is that magnitude maximum? r (d) if r = 4.00 cm and q = 9.00 µc, what is the maximum magnitude? n/c