The force between two small charged spheres having charges of \(2\times 10^{-7}\) C and \(3\times 10^{-7}\) C placed \(30\) cm apart in the air is:
1. \(6 \times 10^{-3}~ \mathrm{N}\)
2. \(5 \times 10^{-3}~ \mathrm{N}\)
3. \(4 \times 10^{-4}~ \mathrm{N}\)
4. \(5 \times 10^{-4}~ \mathrm{N}\)

The electrostatic force on a small sphere of charge 0.4 µC due to another small sphere of charge –0.8 µC in the air is 0.2 N. The distance between the two spheres is:

1. 14 cm
2. 12 cm
3. 16 cm
4. 10 cm

Dimensional formula of $\frac{k{e}^2}{G{m}_e{m}_p}$ is:
1. [M¹L¹T¹]
2. [M⁰L¹T¹]
3. [M⁰L⁰T⁰]
4. [M^-1L⁰T²]

Four point charges q_A = 2μc, q_B = -5μc, q_C = 2μc and qD = -5μc are located at corners of a square ABCD of side 10 cm. The force on a charge of 1μc placed at the center of the square is:

1. 2 N
2. 1 N
3. 5 N
4. 0 N

Two insulated charged copper spheres A and B have their centers separated by a distance of 50 cm. What is the mutual force of electrostatic repulsion if the charge on each is  $6.5\times {10}^{-7} C$? The radii of A and B are negligible compared to the distance of separation.
1. 1.52 × 10⁻² N
2. 3.7 × 10⁻² N
3. 2.01 × 10⁻² N
4. 2.23 × 10⁻¹ N