Figure 21.1b A point charge Q = -500 nC and two unknown point charges, q 1 and q 2, are placed as shown. The electric field at the origin O, due to...

Figure 21.1bA point charge Q = -500 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. 21.1b, the charge q 1, in nC, is closest to: 130 -120 250 -210 120