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Two point charges of $+2\ \mu$C and $+3\ \mu$C are placed $30$ cm apart. The Coulomb force between them is:
A$0.054$ N, attractive between the two charges on the board
B$0$ N, since like charges do not interact at distance
C$0.6$ N, repulsive by $F = kq_1q_2/r^2$
D$60$ N, ignoring the $r^2$ in the denominator
Answer & Solution
Correct answer: C. $0.6$ N, repulsive by $F = kq_1q_2/r^2$
$F = 9\times 10^9\cdot 2\times 10^{-6}\cdot 3\times 10^{-6}/(0.3)^2 = 0.6$ N, repulsive.
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