help with practice test problem! curved rod with charge density?? Two plastic rods are curved. The left rod is a 120° circular arc of radius R, and has uniform charge density λ. The rod on the right is a 120° circular arc of radius 2R, and has uniform charge density -2λ. A point P is located at the center of the circular arcs. Use i (i hat), j (j hat) notation in the following, where i is a unit vector that points in the positive x direction. a) What is the vector Eλ at P due only to the rod with charge density λ? Solution: magnitude = Eλ = λ √(3) / 4∏(ε naught)R Eλ = (λ (√3) / 4∏(ε naught)R) (√3/2 i hat - 1/2 j hat) What i got for the magnitude: λ / 4∏(ε naught)r2) Im having a hard time visualizing the picture. I know I use the Electric field formula Kq/r2. but i dont understand how my teacher got the √3 in the numerator and why its only R instead of R2 in the denominator. Also why is the direction (√3/2 i hat - 1/2 j hat)? Help please!!!! i think i might have a better idea. i take the integral from 0 to pi/3. charge density lambda = Q / L. L = 2 pi R/4 ---> charge density lambda = 2Q / pi R?