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) → $3.6 × 10^{-8} N$
Given:
Each charge, $q = 2 \text{ nC} = 2 \times 10^{-9} \text{ C}$
Separation, $r = 1 \text{ m}$
Medium: air (take $k = \frac{1}{4\pi\varepsilon_0} = 9 \times 10^9 \, \text{N·m}^2\text{/C}^2$)
Repulsive electrostatic force between the two charges:
$F = k \frac{q^2}{r^2}$
Substitute values:
$F = 9 \times 10^9 \times \frac{(2 \times 10^{-9})^2}{(1)^2}$
$F = 9 \times 10^9 \times 4 \times 10^{-18}$
$F = 36 \times 10^{-9} = 3.6 \times 10^{-8} \, \text{N}$
Since the charges repel, the string experiences equal and opposite tension equal to this force.
Final Answer:
$T = 3.6 \times 10^{-8} \, \text{N}$