[填空题]
A charge Q is transferredfmb+ 7qrx(ip/ zkp:)e h9:(bcfb4 +tqtk y. ff from an initially uncharged plastic ball to an identical ball 12 cm away. The force of attraction is then 17 mN. How many electrons were transferre+qfb:bfk fych9tt 4(.d from one ball to the other? $ \times10^{ 12}$ electrons
