Earth's lower atmosphere contains negative and positive ions that are produced by radioactive elements in the soil and cosmic rays from space. in a certain region, the atmospheric electric field strength is 118 v/m and the field is directed vertically down. this field causes singly charged positive ions, at a density of 503 cm-3, to drift downward and singly charged negative ions, at a density of 628 cm-3, to drift upward (see the figure). the measured conductivity of the air in that region is 2.69 × 10-14 (ω-m)-1. calculate (a) the magnitude of the current density and (b) the ion drift speed, assumed to be the same for positive and negative ions.