s2 Electric field E 2.1 Electric field Electric source Electric field- Electric charge E、F Electric field for point charge F 1 goro 0 4丌六 qo4兀E0r Collection of point charge F E ∑Ek=∑ 4兀 r superposition of electric field§2 Electric field E 2.1 Electric field Electric source Electric field Electric charge q0 F E   = Electric field for point charge 0 2 0 4 0 1 r r qq F    = 0 2 0 4 0 1 r r q q F E     = =     = = = k k k k k r r q E q F E 0 2 0 0 4 1 k k k      Collection of point charge superposition of electric field