In an oil drop experiment, negatively charged droplets of equal mass (2.93 10⁻¹⁵ ~kg ) are studied as they fall through vacuum. An electric field of magnitude 5.92 10^4 ~N / C , pointing downwards, is present. It is observed that a droplet of charge Q₁ remains suspended while another with charge Q₂ falls through 0.125 m from rest in 0.25 s . The Q₁ / Q₂ is closest to,