The force between two small charged spheres having charges of $2 imes 10^{-7}$ C and $3 imes 10^{-7}$ C pl

Question

The force between two small charged spheres having charges of $2 	imes 10^{-7}$ C and $3 	imes 10^{-7}$ C placed 30 cm apart in the air is:

Accepted Answer

The force between two point charges in air is given by Coulomb's Law: $F = \frac{1}{4\pi\varepsilon_0} \frac{q_1 q_2}{r^2}$. 
Given:
$k = \frac{1}{4\pi\varepsilon_0} = 9 	imes 10^9$ N m$^2$ C$^{-2}$
$q_1 = 2 	imes 10^{-7}$ C
$q_2 = 3 	imes 10^{-7}$ C
$r = 30$ cm = $0.3$ m

Substituting these values:
$F = \frac{(9 	imes 10^9) 	imes (2 	imes 10^{-7}) 	imes (3 	imes 10^{-7})}{(0.3)^2}$
$F = \frac{54 	imes 10^{-5}}{0.09} = \frac{54 	imes 10^{-5}}{9 	imes 10^{-2}}$
$F = 6 	imes 10^{-3}$ N

(Note: This matches NCERT Physics Class 12, Chapter 1, Exercise 1.1).

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