Question

Two point charges $+ 3\mu C$and $+ 8\mu C$ repel each other with a force of 40 N. If a charge of$- 5\mu C$ is added to each of them, then the force between them will become

• A. $- 10N$
• B. $+ 10N$
• C. $+ 20N$
• D. $- 20N$

Answer 1

Answer: (A)

$- 10N$

Answer 2

Initially $F = k \times \frac{3 \times 8 \times 10^{- 12}}{r^{2}}$ and Finally

$F' = - k\frac{2 \times 3 \times 10^{- 12}}{r^{2}}$ so $\frac{F'}{F} = - \frac{1}{4}$ ⇒$F' = - 10N$