A point charge Q = -400 nC and two unknown point charges, q 1 and q 2, are placed as shown. The electric field at the origin O, due to charges Q, q...

A point charge Q = -400 nC and two unknown point charges, q 1 and q 2, are placed as shown. The electric field at the origin O, due to charges Q, q 1, and q 2, is equal to zero. In Fig. 21.1c, the charge q 2, in nC, is closest to: