Electric field due to the system of point charges

When a number of point charges are distributed through space, the electric field they jointly produce at some field point P is found using the same superposition principle used earlier for forces. The field at P due to the collection of point charges is simply the vector sum of the individual fields that each charge would produce at P if it were the only charge present: E_total(P) = E1(P) + E2(P) + ... + En(P), where each Ei(P) = k(qi/r_iP^2) r-hat_iP is the ordinary point-charge field due to charge qi alone, computed exactly as in section 1.3.1, using the distance and direction from qi to P. Because each individual contribution Ei is unaffected by the presence of the other charges, this vector sum gives the exact resultant field, not merely an approximation -- the same logical structure, and the same practical procedure of resolving each contribution into components before adding, that was used in …