14. Since the forces involved are proportional to q, we see that the essential difference between the two situations is Fa∝qB+ qC(when those two charges are on the same side) versus Fb∝−qB+ qC(when they are on opposite sides). Setting up ratios, we have FaFb= qB+ qC-qB+ qC¡20.14-2.877= 1 + r-1 + rwhere in the last step we have canceled (on the left hand side) 10
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