Two particles carrying a charge of 2 nC each connected by an insulating string are placed 1 m apart on a smooth horizontal surface. The tension in the string is
Answer & explanation
Correct answer: option 2
The correct answer is Option (2) → \( 3.6 \times 10^{-8}\,\mathrm{N} \)
The like charges repel each other. The surface is smooth, so the only thing holding each particle in place is the string: the tension equals the Coulomb repulsion.
\( \displaystyle T = F = \frac{1}{4\pi\varepsilon_0}\,\frac{q_1 q_2}{r^{2}} \)
\( q_1 = q_2 = 2\,\mathrm{nC} = 2\times10^{-9}\,\mathrm{C} \)
\( r = 1\,\mathrm{m} \)
\( \displaystyle T = \frac{9\times10^{9} \times (2\times10^{-9})^{2}}{1^{2}} = 9\times10^{9} \times 4\times10^{-18} = 3.6\times10^{-8}\,\mathrm{N} \)