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

$3.6 × 10^{-8} N$

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:

$T = 3.6 \times 10^{-8} \, \text{N}$