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1. Electric Charges and Fields
medium
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....$N$
A
$ - 10$
B
$ + 10$
C
$ + 20$
D
$ - 20$
Solution
(a) In second case, charges will be $ – \,2\,\mu C$ and $ + 3\,\mu C$
Since $F \propto {Q_1}{Q_2}$ i.e. $\frac{F}{{F'}} = \frac{{{Q_1}{Q_2}}}{{Q{'_1}Q{'_2}}}$
$\frac{{40}}{{F'}} = \frac{{3 \times 8}}{{ – 2 \times 3}} = – 4$ $==>$ $F' = 10\,N$(Attractive)
Standard 12
Physics
