Discussion
Force between two charges +8 μC and +2 μC is 16 N. If the charges are brought into contact and then separated by the same distance, the force between them is
Answer: A
The new force is 25 N.
Coulomb's force is proportional to the product of the charges at a fixed separation. On contact, identical conductors share the total charge equally: \(\frac{8 + 2}{2} = 5\ \mu\text{C}\) each.
\[ \begin{aligned} \frac{F'}{F} &= \frac{5 \times 5}{8 \times 2} = \frac{25}{16} \\ F' &= 16 \times \frac{25}{16} = 25\ \text{N} \end{aligned} \]
The force increases because, for a fixed total, the product is largest when the charges are equal. 20 N and 15 N are slips in the ratio, and 16 N (not offered) would assume nothing changes.
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